Manaaki Taha Moana: Enhancing Coastal Ecosystems for Iwi
Report No. 1
June 2011
Health of Te Awanui Tauranga
Harbour
Health of Te Awanui Tauranga Harbour
Jim Sinner, Dana Clark, Joanne Ellis, Bethany Roberts, Weimin Jiang, Eric Goodwin
(Cawthron Institute)
Lydia Hale, Shadrach Rolleston* (Waka Taiao)
Murray Patterson, Derrylea Hardy, Emma Prouse, Shanandore Brown#
(Massey University)
ISBN 978-0-9876535-0-5
ISSN 2230-3332 (Print)
ISSN 2230-3340 (Online)
Published by the Manaaki Taha Moana (MTM) Research Team
Funded by the Ministry for Science and Innovation
Contract MAUX0907
Main Contract Holder: Massey University
www.mtm.ac.nz
* Employed by Massey University for the early stage of work on this report, and contracted by Waka Taiao for the
latter stage.
#
Employed by Massey University, but located in the Waka Taiao office.
Reviewed by:
Approved for release by:
Professor Chris Battershill
MTM Science Leader
Professor Murray Patterson
Issue Date: June 2011
Recommended citation:
Sinner J, Clark D, Ellis J, Roberts B, Jiang W, Goodwin E, Hale L, Rolleston S, Patterson M, Hardy D, Prouse E, Brown S. 2011.
Health of Te Awanui Tauranga Harbour. Manaaki Taha Moana Research Report No. 1. Cawthron Report No.1969. Palmerston North:
Massey University.
© Copyright: Apart from any fair dealing for the purpose of study, research, criticism, or review, as permitted under the Copyright Act, this publication must
not be reproduced in whole or in part without the written permission of the Copyright Holder, who, unless other authorship is cited in the text or
acknowledgements, is the commissioner of the report.
Mihi
He hōnore, he kororia ki te Atua
He maungarongo ki te whenua
E rere ana nga whakaaro ki a rātou kua peka atu ki tua o Pairau
Haere, haere, hoki atu rā
E tangi tonu ki a rātou Otautahi whānui
Ngāti Rarua, e mihi nei
Tauranga moana, e mihi nei
Ko Ngāti Ranginui, Ngaiterangi, Ngāti Pukenga me tou tātou whānau a Waitaha whānui tonu.
Otira ki te waitai o Te Awanui
E rerere – te au kume o Tangaroa e
Tihei Mauri Ora.
Manaaki Taha Moana Report No. 1
iii
© Manaaki Taha Moana Research Team
Published by the Manaaki Taha Moana Research Team
MAUX 0907 Contract Holder:
Massey University
Private Bag 11052
Palmerston North
New Zealand
Revision history
1
Revised caption for Figure 2.
Re-scanned and re-inserted Figure 5
Minor formatting and typographical corrections.
Reference changed from Wildland Consultants Ltd. (2003)
to: Beadel S., Maseyk F., Garrick A., Pierce R., Bawden R.,
Honey M. (2003).
2
Correction on p.ix. “non-commercial catch” changed to
“commercial catch”. Various other minor formatting and
typographical corrections.
7 July 2011
28 Nov 2011
Disclaimer
While the author(s), the MTM research team and their respective organisations, have exercised all
reasonable skill and care in researching and reporting this information, and in having it appropriately
reviewed, neither the author(s), the research team, nor the institutions involved shall be liable for the
opinions expressed, or the accuracy or completeness of the contents of this document. The author will
not be liable in contract, tort, or otherwise howsoever, for any loss, damage or expense (whether direct,
indirect or consequential) arising out of the provision of the information contained in the report or its
use.
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Manaaki Taha Moana Report No. 1
EXECUTIVE SUMMARY
This report summarises what is currently known about the ecological health of Tauranga
Harbour – traditionally known to local iwi as Te Awanui – in order to inform the Tauranga
community, iwi and stakeholders of the ‘state of the harbour’ and to identify information gaps
and priorities for field research. The report is based on a literature review of published
scientific papers and technical reports; it did not extend to new field work or new analysis and
interpretation of data.
Manaaki Taha Moana (MTM) is a six-year programme, running from October 2009 to
September 2015, with research being conducted primarily in two areas: Tauranga moana and
coastal rohe of Ngāti Raukawa on the Horowhenua coast. The wider research project aims to
restore and enhance coastal ecosystems and their services of importance to iwi/hapū, by
working with iwi to improve knowledge of these ecosystems and the degradation processes
that affect them.
This report begins with a description of land use in the catchment and the history of
development, because water quality and the ecological health of the harbour are directly
affected by land use within the catchment. We then review current information on water
quality, factors that influence water quality, the flora and fauna of the harbour and the
ecosystem services provided by the harbour. These subjects are considered in turn before
identifying current information gaps and priorities for future research.
Physical description of the harbour
Tauranga Harbour is a large estuary (approximately 200 km2) protected from the Pacific Ocean
by a barrier island (Matakana Island) and two barrier tombolos, Bowentown at the northern
entrance and Mount Maunganui to the south. Two harbour basins are separated by large
intertidal flats in the central area of the harbour and, although the two basins are connected,
there is little water exchange between the two. The two main entrances to the harbour are at
either end of Matakana Island where the tide flows strongly through deep channels. The rest of
the harbour is shallow, typically less than 10 m deep, with intertidal flats comprising
approximately 66% of its total area. The Port of Tauranga, established in 1873, is located near
Mount Maunganui and maintenance dredging has been regularly required to maintain adequate
channel depths.
Land use, wetlands and sediments
The Tauranga Harbour catchment covers 1,300 km² and is home to about 150,000 people. It
receives discharges from many separate catchments originating in the Kaimai-Mamaku range.
The northern harbour catchments cover an area of 270 km2 while the southern harbour
catchments cover 1,030 km2. As of 2004, the land cover in the Tauranga Harbour catchment
was predominately pasture and indigenous forest.
Manaaki Taha Moana Report No. 1
v
Wetlands have many ecological functions including the provision of fish and wildlife habitat,
flood storage, shoreline erosion protection and natural water quality treatment. Specifically,
wetlands improve coastal water quality by acting as a physical and biochemical filter to
immobilize sediment and pollutants from water as it runs off the land. In the North Island,
only 5% of original wetland area remains intact.
Between 1840 and 1991, freshwater wetland area around Tauranga Harbour declined by 84%
while estuarine wetland area in Tauranga Harbour increased by 17%, reflecting a marked
increase in mangrove vegetation. Approximately 700 ha of saltmarsh have been lost since
1840 due to land reclamation.
Sedimentation rate depends primarily on land slope, soil type, rainfall and land use. Land in
pasture currently makes the largest contribution to sediment load in Tauranga Harbour (63% of
total). Forested areas contribute 27% of the total sediment load. In the southern half of the
harbour, the highest rates of deposition occur in the following sub-estuaries: Te Puna inner, the
mouth of the Waipapa River and Mangawhai Bay inner.
Sedimentation affects many aspects of harbour ecology. It makes sheltered estuaries muddier
and shallower and reduces water clarity. Direct impacts are likely to include clogging the gills
of filter feeders (e.g. cockles, pipi, scallops), reductions in the settlement success and survival
of larval and juvenile phases of shellfish (e.g. paua), reductions in the foraging abilities of
finfish (e.g. juvenile snapper) and decreases in the food available to benthic species. The
accumulation of nutrients, pesticides, heavy metals and hydrocarbon residues in shallow
estuaries can also adversely affect marine organisms.
Chronic sedimentation will eventually lead to changes in the species mix of benthic
communities and modification of ecologically important habitats, especially those composed
of habitat forming species such as seagrass beds, green-lipped and horse mussel beds,
bryozoan and tubeworm mounds, kelp forests, sponge gardens and mangrove habitats.
While sediment accumulation rates on intertidal flats in Tauranga Harbour are low compared
to other North Island estuaries, sedimentation in more sheltered areas with higher
accumulation rates has been implicated in the decline of seagrass and expansion of mangroves,
as noted below. Climate models have projected a 43% increase in mean annual sediment load
to the southern harbour by the year 2051. The projected increase is even larger in many
sheltered estuaries (e.g. Bellevue 94%, Matakana (1) 48%, Waitao 47%).
Nutrients and other pollutants
Recent studies have found that levels of nitrogen and phosphorus have shown little change
within Tauranga Harbour between the early 1990s and 2005. Most major point source
discharges of nitrogen and phosphorous were removed from the harbour in the early to mid
1990s. In many rivers and streams entering the harbour, nutrient levels have declined due to
improved rural practices and better control of surface runoff and land use changes. However,
many of these rivers still have elevated nutrient levels, and some show increasing trends
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Manaaki Taha Moana Report No. 1
associated with agriculture and runoff from recently harvested forest. Omanawa, Kopurererua,
Waimapu and Rocky streams had elevated nitrogen concentrations while phosphorus levels
were highest in the Rocky and Kopurererua streams.
Despite frequent bacterial contamination in rivers and streams within the catchment, the
microbiological water quality standards for recreation are rarely exceeded in Tauranga
Harbour, although shellfish contamination can occur. Bacterial contamination in Tauranga has
many possible sources: wastewater treatment plants and leaky pipes, septic tanks, livestock
farming, birds, marine vessels and meat processing plants. Seepages have been detected from
Te Maunga oxidation ponds, while Tanner’s Point, Ongare Point and Te Puna have been
identified as areas with on-site wastewater treatment systems (e.g. septic tanks) that pose a risk
to water quality.
A number of studies have examined pollutants within Tauranga Harbour, including plastic
particles, polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs,
commonly derived from incomplete combustion of petroleum and coal products), DDT, resin
acids and heavy metals. While most of these substances were deemed to be within Australian
and New Zealand Environment and Conservation Council (ANZECC) guidelines, exceedances
were noted for some heavy metals and PAHs. Stormwater outlets that drain from industrial
areas were identified as the key source of pollutants to the Tauranga Harbour. Te Maire Rd
industrial area was an area of high contamination, exceeding at least the lower ANZECC
guideline value for every metal except mercury. Zinc levels exceeded at least the lower
guideline value for all sites bar one. PAHs and also exceeded the lower ANZECC guideline
value in sediments surrounding stormwater drains.
It is difficult to determine accurately what constitutes low and high risk contamination because
the effect of a pollutant on aquatic organisms depends on the habitat environment and the
sensitivity of the species, and may only manifest itself over time. Heavy metals are generally
toxic and tend to accumulate and persist in harbours and estuaries due to restricted water
circulation and on-going inputs from the surrounding catchment. Areas with multiple toxins
may be exposed to greater environmental risk due to compounding effects of pollutants.
There can also be problems in the food chain where higher order predators consume
contaminated organisms and accumulate toxins (bioaccumulation), creating the potential for
human health impacts via contaminated seafood. Shellfish monitoring indicates that copper
and zinc levels were higher in shellfish from the Plumbers Point/Te Puna site than other
locations in the harbour.
Marine flora
Phytoplankton biomass in Tauranga Harbour varies over time and is dominated by diatoms.
Monitoring of phytoplankton in Tauranga Harbour commenced in 2003. Since 2008, shellfish
collection closures have regularly occurred in the harbour as a result of toxic phytoplankton
species.
Manaaki Taha Moana Report No. 1
vii
At least 23 species of macroaglae have been identified within the harbour, with red turf-like
algae identified as the most common. Sea lettuce blooms have occurred in the harbour as far
back as the 1940s and monitoring since 1991 shows large blooms occurred in 1991-1993, 1998
and 2003-2007. Sea lettuce blooms peak in spring and decline over late summer, when growth
appears to be nutrient limited. Greater sea lettuce abundance was recorded during El Niño
years when nutrient-rich deep waters upwell offshore and enter the harbour; further research is
required to understand the factors that affect sea lettuce growth.
Seagrass beds enhance primary production and nutrient cycling, stabilize sediment, protect the
coast from erosion and support a number of animals and plants. They also provide a nursery
habitat for juvenile fish. Seagrass beds declined by 34% from 1959 to 1996, with a 90%
decrease in subtidal areas. Sub-estuaries with large catchments showed greater loss of
seagrass, with sedimentation and nutrient loading implicated as the main factors causing
seagrass decline in Tauranga Harbour. There are currently no proposed restoration plans but
studies in Whangarei Harbour show this may be a viable option in the future.
Finally, while area in mangroves is declining globally, in New Zealand it is increasing.
Mangroves in Tauranga Harbour have expanded from 240 ha in 1943 to 623 ha in 2003. Two
main mechanisms account for the spread of mangroves, both directly driven by increased
sedimentation. More sediment settling in the harbour raises the level of the intertidal seabed,
allowing mangroves to colonise areas that were once too frequently inundated by the tide.
Once established, mangroves reduce water movement and wind, further enhancing fine
sediment deposition and creating a positive feedback as the extent of suitable habitat for
mangrove colonization increases.
In Tauranga Harbour, approximately 90 ha of mangroves have been removed in the past few
years, in response to community concerns over the spread of mangroves (reduced access to the
water, loss of views, unpleasant odours, change in marine life, etc). Mangrove management
initiatives are becoming more catchment focused, to reduce sedimentation that contributes to
spread of mangroves. Although their expansion can be seen as a problem, mangroves provide
many important ecological functions including trapping sediments, reducing coastal erosion,
providing important nursery habitats for some species (short-finned eel, parore, grey mullet)
and in nitrogen cycling. The removal of mangroves has been linked with mortality of epifauna
and infauna, anoxic sediments and associated decreases in oxygen in the water column in
cleared areas. Further research is being conducted to determine the ecological consequences of
both mangrove removal and expansion on these habitats.
Marine fauna
Marine fauna include macroinvertebrates (e.g. sponges, anemones, worms, shellfish, crabs,
starfish and sea urchins) fish, birds and mammals. Within Tauranga Harbour, soft sediment
macrobenthic communities are similar to those in comparable habitats elsewhere in northern
New Zealand. Polychaetes are the dominant taxonomic group in subtidal areas while bivalves
dominate intertidal areas.
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Manaaki Taha Moana Report No. 1
Shellfish and other marine invertebrates
A 1994 study reported that subtidal species diversity was limited by sediment mobility with
fewer species in areas with low silt deposition (due to strong currents). Intertidal species
diversity showed a strong negative correlation with silt content. Macroinvertebrate diversity
was higher in seagrass beds than on bare sand. Studies of the rocky communities at the
harbour entrance indicated these areas are very diverse with high densities of filter feeding
species. Cockles, wedge shells and pipi all showed a pattern of larger individuals near the
harbour entrance with progressively smaller ones in the upper harbour. Cockles showed no
change in length frequencies between 1974 and 1994 and macroinvertebrate species richness,
an indicator of ecosystem health, remained stable over the 1990-2000 period. Evidence of
extensive former mussel beds has been found near the Bowentown entrance to the harbour; the
loss of these beds has been attributed to overfishing.
Cockles and pipi have been monitored by the Ministry of Fisheries at Otumoetai, near the
southern entrance to Tauranga Harbour, five times between 2001 and 2010. Pipi from
Otumoetai exhibited a negative trend, with estimated total numbers down by 50% in 2010
compared to the 2006 survey. In contrast, the total number of cockles in 2007 and 2010 was
significantly higher (up about 200%) compared to 2006 and earlier surveys, although the
proportion of cockles of harvestable size was still low, around 1%.
Fish
Studies have found that yellow-eyed mullet are the most abundant fish species in Tauranga
Harbour. Within the mangrove forests, yellow-eyed mullet remains the dominant species,
followed by smelt and short-finned eel.
Commercial catch is reported at a scale not useful for assessing fisheries in Tauranga Harbour,
so there is little quantitative evidence of trends in the status of most fish stocks. Both
commercial and recreational harvests of snapper have fallen, but the recreational catch is still
over 40 tonnes, dwarfing the commercial catch. Tangata whenua have noticed a decline in
many fish species including flounder, shark, snapper, kingfish, trevally and mullet. They have
raised concerns over the amount of bycatch being wasted by commercial fishers and fishing
methods, such as drag netting, which they believe to have adverse effects on benthic habitat.
A commercial fisher has also noted changes in fish communities. No new permits are being
issued by the Ministry of Fisheries for dragnetting inside the harbour. A mataitai reserve of 6
km2 was established in 2008 around Mt Maunganui; commercial fishing is prohibited within
this area and restricted in many other parts of the harbour.
Marine mammals
New Zealand fur seals are common visitors to the harbour and leopard and elephant seals are
occasionally sighted. More than 30 cetacean species (whales, dolphins and porpoises) have
been observed in the Bay of Plenty and at least eight mammal species have been observed
within the harbour. There is no statistically robust data that would enable population trends to
be determined.
Manaaki Taha Moana Report No. 1
ix
Birdlife
Tauranga Harbour is recognized as a wetland of international significance for the protection of
migratory and resident bird species. These include birds whose population status is “nationally
critical” (black stilt, grey duck and white heron), nationally endangered (bittern and blackbilled gull), and several that are nationally vulnerable. During summer, Matakana Island hosts
the largest breeding colony of New Zealand dotterel in the country, as well as a large postbreeding flock during winter.
Wading bird species showed mixed population trends over the period 1984-2010. Of 11
species that have been counted biannually, four had an increasing population trend, five had a
decreasing trend, and others were mixed or insignificant. Dotterel numbers increased
significantly, thought to be attributable to protection on Matakana Island.
Mount Maunganui hosts one of the few remaining mainland colonies of grey-faced petrel.
Research indicates that the Mount Maunganui petrel population has been stable since at least
1990, although predation from rats and mustelids are a concern given the petrel’s low
reproduction rate. Black swan and paradise shelduck populations show no significant trend,
but there was a significant increase in Canada geese in the Bay of Plenty region during the past
decade.
Invasive species
Surveys at the Port of Tauranga have found twelve non-native marine species including three
that were new to New Zealand. Noteworthy among these are the Asian date mussel,
Didemnum vexillum, the Asian kelp Undaria and a dinoflagellate. Another non-native species,
the sea squirt Styela clava, is well established in the Hauraki Gulf and is a potential threat to
Tauranga Harbour because of the amount of vessel traffic between the two areas. The Port of
Tauranga also remains vulnerable to new pest incursions from overseas, given the high level of
incoming vessel traffic.
While some of these invasive species have the potential to cause significant ecological, social
or economic harm, there is no evidence that they have yet caused significant harm in Tauranga
Harbour. The extent of spread beyond the port environment is generally unknown but there are
no indications of invasive species causing significant problems in the wider harbour.
Health of Tauranga Harbour
There is limited recent scientific evidence describing the overall condition of the harbour, and
the indications are mixed. Time series data is available only since the early 1990s, and only for
some indicators, and does not reveal any significant trends for nutrients and benthic
communities. However, intertidal seagrass beds have declined significantly, and sub-tidal beds
were almost gone by 1996; their fate since then is unknown. Sedimentation has been linked to
expansion of mangroves and is almost certainly causing other changes to harbour ecology, but
these have not been documented. Changes to fish and shellfish abundance have been noted
anecdotally but there is no time series data with which to assess the extent of change.
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Manaaki Taha Moana Report No. 1
Priorities for further research
While studies have been conducted on a wide range of topics about the ecology of Tauranga
Harbour, understanding of the overall processes that drive the estuarine ecosystem is far from
complete. In summarising this body of literature, a number of information gaps have become
apparent.
The spatial scale over which information has been collected varies greatly from one study to
the next. In order to understand more fully the role of various anthropogenic stressors on
biodiversity, we suggest conducting a broad scale survey of Tauranga Harbour. In contrast to a
fine scale survey, which provides detailed information on a relatively small area, a broad scale
survey would involve sampling flora and fauna over the larger spatial scale of the entire
estuary and collecting associated sediment samples to quantify sedimentation, nutrients and
pollutants at each site. The survey would provide more current and detailed information to
quantify macroinvertebrate communities, biodiversity and the presence or loss of functional
groups such as shellfish species across the harbour. The collection of physical data at the same
sites as biological data would enable changes in community composition to be linked with
changes in key anthropogenic stressors such as sediments, nutrients and pollutants. This
information could then also be used by iwi and researchers to prioritise research questions for
further study.
Specific case studies could focus on shellfish, seagrass beds and mangrove expansion.
Shellfish, seagrass beds and mangrove habitats are identified for further research due to their
cultural and ecological importance and due to documented impacts on these ecosystem
components. Other knowledge gaps and possible research topics are also identified in the
report.
Manaaki Taha Moana Report No. 1
xi
TABLE OF CONTENTS
EXECUTIVE SUMMARY ....................................................................................................... V
1.
INTRODUCTION ........................................................................................................... 1
1.1.
Background ............................................................................................................................................... 1
1.2.
1.2.1.
1.2.2.
1.2.3.
1.2.4.
The Manaaki Taha Moana project ............................................................................................................. 1
Study areas and personnel ....................................................................................................................... 1
MTM objectives ......................................................................................................................................... 2
Fit with other MTM work ............................................................................................................................ 3
Next steps ................................................................................................................................................. 4
1.3.
Outline of this report .................................................................................................................................. 4
2.
2.1.
DESCRIPTION OF THE HARBOUR ............................................................................. 5
Location and hydrodynamics ..................................................................................................................... 5
2.2.
The catchment area .................................................................................................................................. 7
2.3.
Climate .................................................................................................................................................... 11
2.4.
Settlement of the harbour ........................................................................................................................ 11
3.
WETLANDS AND WATER QUALITY ...........................................................................14
3.1.
3.1.1.
3.1.2.
Wetlands ................................................................................................................................................. 14
Bay of Plenty wetlands ............................................................................................................................ 15
Wetlands in Tauranga Harbour ............................................................................................................... 16
3.2.
3.2.1.
3.2.2.
3.2.3.
3.2.4.
3.2.5.
Sedimentation ......................................................................................................................................... 18
Sediment inputs to the harbour ............................................................................................................... 18
Dynamics ................................................................................................................................................ 20
Future predictions.................................................................................................................................... 23
Impact on flora and fauna........................................................................................................................ 23
Dredging activity ...................................................................................................................................... 25
3.3.
Nutrients .................................................................................................................................................. 25
3.4.
Pollutants ................................................................................................................................................ 27
3.5.
3.5.1.
3.5.2.
3.5.3.
Bacterial contamination ........................................................................................................................... 30
Sewage systems in the Tauranga region ................................................................................................ 31
Recreational bathing sites ....................................................................................................................... 33
Shellfish contamination ........................................................................................................................... 36
4.
FLORA AND FAUNA OF THE HARBOUR ...................................................................37
4.1.
4.1.1.
4.1.2.
4.1.3.
Marine flora ............................................................................................................................................. 37
Phytoplankton ......................................................................................................................................... 37
Macroalgae ............................................................................................................................................. 38
Other marine plants ................................................................................................................................. 43
4.2.
4.2.1.
4.2.2.
4.2.3.
4.2.4.
Marine fauna ........................................................................................................................................... 51
Macroinvertebrates, including shellfish.................................................................................................... 52
Finfish...................................................................................................................................................... 61
Marine mammals ..................................................................................................................................... 68
Birds ........................................................................................................................................................ 70
4.3.
Invasive species ...................................................................................................................................... 76
5.
CONCLUSIONS AND RESEARCH RECOMMENDATIONS.........................................79
5.1.
The health of Tauranga Harbour ............................................................................................................. 79
5.2.
Broad scale survey .................................................................................................................................. 79
5.3.
Possible research on shellfish populations .............................................................................................. 81
Manaaki Taha Moana Report No. 1
xiii
5.4.
Possible research on seagrass ............................................................................................................... 82
5.5.
Possible research on mangrove ecosystems .......................................................................................... 83
5.6.
Summary ................................................................................................................................................. 83
6.
ACKNOWLEDGEMENTS .............................................................................................85
7.
REFERENCES .............................................................................................................86
8.
APPENDICES ..............................................................................................................99
8.1.
8.1.1.
8.1.2.
8.1.3.
8.1.4.
8.1.5.
8.1.6.
8.1.7.
8.1.8.
Appendix 1: Agencies with management functions relevant to Tauranga Harbour ................................. 99
Bay of Plenty Regional Council ............................................................................................................... 99
Territorial Authorities ............................................................................................................................. 101
Department of Conservation ................................................................................................................. 102
Ministry of Fisheries .............................................................................................................................. 103
MAF Biosecurity New Zealand .............................................................................................................. 103
Maritime New Zealand .......................................................................................................................... 104
Ministry for the Environment .................................................................................................................. 104
Fish and Game New Zealand ................................................................................................................ 105
8.2.
Appendix 2: Community composition of submerged reef biota off Motuotau Island .............................. 106
8.3.
Appendix 3: Birds of Tauranga Harbour ................................................................................................ 108
LIST OF FIGURES
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Figure 8.
Figure 9.
Figure 10.
Figure 11.
Figure 12.
Figure 13.
Figure 14.
xiv
Tauranga Harbour showing the dividing line between the northern and southern basins.
Inset shows the wider Bay of Plenty region. ....................................................................... 6
The catchments of the Kaimai-Mamaku Range. Catchments drain to Tauranga Harbour
except Waihi, Paeroa, Te Aroha, Middle and Upper Waihou, which drain to Hauraki Gulf.
LUC is Land Use Capability classification, with Class 1 the most versatile land (the least
limitations for productive use) and at the other end of the scale Class 8, which is not
suitable for productive use (most limitations). Source: (Shaw et al., 2010). ...................... 8
Geological map of Tauranga and the southern Kaimai Range. Inset shows location of
Coromandel and Taupo Volcanic Zones in the North Island, New Zealand. Ma = million
years ago. Source: (Briggs et al., 2005). ........................................................................... 9
Land cover within the Tauranga Harbour catchment in 2008. Source: (Bay of Plenty
Regional Council based on LUCAS land use database from the Ministry for the
Environment.) .................................................................................................................... 10
Land cover in Tauranga District in 1840 (top) and 2000 (bottom). Source: (Wildland
Consultants Ltd., 2000). .................................................................................................... 12
Activity at the Port of Tauranga (photos: Noel Peterson). ................................................ 13
Approximate location of sub-catchments in the southern Tauranga Harbour as defined by
Hume et al. 2010. Inset shows wider Tauranga Harbour. Note that for some subcatchments, only part of the sub-catchment area is shown. ............................................. 20
Approximate location of sub-estuaries in the southern Tauranga Harbour as defined by
Hume et al. 2010. Grey shading shows deep channels within the harbour and inset
shows the wider Tauranga Harbour. The location of Bluegum Bay is also identified. ..... 22
Monitoring sites for metals and PAH contaminants in and near Tauranga Harbour 20062008. Inset shows location of Tauranga Harbour within the North Island of New Zealand.
Source: (Park, 2009). ........................................................................................................ 28
Bay of Plenty Regional Council monitoring sites for bathing water quality. Inset shows
location of Tauranga Harbour in the North Island of New Zealand. Source: (Scholes,
2010). ................................................................................................................................ 34
Sea lettuce (Ulva sp.) in Tauranga Harbour (photos: Noel Peterson) .............................. 40
Seagrass (Zostera capricorni) in Tauranga Harbour (photos: Noel Peterson). ................ 43
Mangrove (Avicennia marina) spread and removal in Tauranga Harbour (photos: Noel
Peterson) ........................................................................................................................... 46
Mangrove cover (ha) in Tauranga Harbour 1943-2003. Data provided by S Park (pers.
comm.). ............................................................................................................................. 48
Manaaki Taha Moana Report No. 1
Figure 15.
Relationship between mud content and mangrove canopy cover in Tauranga Harbour
sub-estuaries Source: (Park, 2004). ................................................................................. 50
Figure 16. Commercial and recreational catch of trevally and snapper in Tauranga Harbour and
Statistical Area 009. Commercial catch for 1984-86 is from Tauranga Harbour, all
methods; data for 1991-1997 are from statistical area 009 for drag net only. Time series
is incomplete due to changes in catch reporting systems. Recreational catch was
estimated in 1984, 1994 and 1996 only, from occasional surveys of recreational fishers.
Source: (MFish, 1998). ..................................................................................................... 63
Figure 17. Recreational fishing on Tauranga Harbour (photo: Noel Peterson). ................................ 66
Figure 18. Area of mataitai fisheries reserve indicated by blue line around Mount Maunganui.
Source: (MFish, 2008). ..................................................................................................... 68
Figure 19. Asian Date mussel. .............................................................................................................. 76
Figure 20. Didemnum vexillum. ............................................................................................................. 77
Figure 21. Undaria pinnatifida. .............................................................................................................. 77
Figure 22. Styela clava. ......................................................................................................................... 77
LIST OF TABLES
Table 1.
Table 2.
Table 3.
Table 4.
Table 5.
Table 6.
Table 7.
Table 8.
Table 9.
Table 10.
Table 11.
Table 12.
Table 13.
Table 14.
Table 15.
Land cover in the ten sub-catchments of Tauranga Harbour ........................................... 10
Sediment load and sediment yield to the southern Tauranga Harbour from various land
uses. These values are before sediment deposition in the stream network. The yields in
this table are averaged over the range of slopes, soils and climate that occur. ............... 19
Sediment load to the southern Tauranga Harbour, with yield and sediment delivery ratio
(SDR) for each sub-catchment. Yield is the load from the sub-catchment to the estuary
divided by the sub-catchment area; SDR is the percentage of sediment generated that
actually reaches the harbour (the rest remains in the stream network)............................ 19
Annual mean fine sediment sedimentation rate, loss of fine sediment to the ocean, mud
content of sediment and mean grain size for sub-estuaries in the southern Tauranga
Harbour. ............................................................................................................................ 21
-1
Concentrations of PAHs and heavy metals (mg kg dry wt) at stormwater impacted sites
in and around Tauranga Harbour standardised to the 63 m (mud) sediment fraction.
ANZECC Interim Sediment Quality Guideline values (ISQG) for “low” (orange font;
possibility of sublethal effects) and “high” (red font; possible toxicity) are provided at the
bottom of the table. ........................................................................................................... 29
Compliance conditions 10.1,10.2 and 11.1 of consent 62878 for the Omanu ocean outfall
and consent conditions for the Katikati ocean outfall........................................................ 32
Surveillance, alert and action levels for bacterial contamination of fresh and marine
waters. ............................................................................................................................... 35
Macroalgae species identified in the 2006 Port of Tauranga survey. Some organisms
were not able to be identified to species level. ................................................................. 39
Mangrove canopy cover (ha) of sub-estuaries within Tauranga Harbour from 1943 to
2003. ................................................................................................................................. 48
Canopy cover (% of sub-estuary) and mud content (% of sediment) in sub-estuaries
within Tauranga Harbour in 2003...................................................................................... 49
The numerically dominant macrofauna species recorded in 1994 subtidal surveys of
Tauranga Harbour using 1 mm mesh sieves. Also reported is the percentage
composition of the total number of individuals from the 96 (13 cm diameter) core samples
collected. ........................................................................................................................... 54
The numerically dominant macrofauna species recorded in 1994 intertidal surveys of
Tauranga Harbour using 2 mm mesh sieves. Also reported is the percentage
composition of the total number of individuals from the 640 (13 cm diameter) core
2
samples collected and the mean and maximum abundances (per m ) of each species. . 56
Species observed at two rocky dive sites near the southern entrance to Tauranga
Harbour in 1988. Fish are not included in this table. ....................................................... 58
Macroinvertebrate species mentioned by Tauranga moana kaumatua and kuia ............. 59
Common fish species within Tauranga Harbour. .............................................................. 61
Manaaki Taha Moana Report No. 1
xv
Table 16.
Table 17.
Table 18.
Table 19.
Fish species observed at two rocky dive sites near the southern entrance to Tauranga
Harbour in 1988. ............................................................................................................... 65
Fish species observed by Tauranga moana kaumatua and kuia in seven fishing grounds
in and around Tauranga Harbour. ‘X’ indicates presence at fishing ground. ................... 67
Conservation status of threatened birds (Miskelly et al., 2008) around Tauranga Harbour.
Common, Māori and scientific names. Photos top to bottom: black stilt, black-billed gull,
Caspian tern, wrybill. ......................................................................................................... 72
Population trends (1984-2010) of eleven wading bird species in Tauranga Harbour. ..... 74
LIST OF APPENDICES
8.1.
8.2.
8.3.
xvi
Appendix 1: Agencies with management functions relevant to Tauranga Harbour .......... 99
Appendix 2: Community composition of submerged reef biota off Motuotau Island ...... 106
Appendix 3: Birds of Tauranga Harbour ......................................................................... 108
Manaaki Taha Moana Report No. 1
Manaaki Taha Moana Report No. 1
xvii
1.
INTRODUCTION
1.1. Background
Tauranga Harbour – known to local iwi as Te Awanui – is an estuary of great cultural
significance to the iwi of Tauranga moana – Ngāti Pūkenga, Ngāiterangi and Ngāti Ranginui.
This report summarises what is currently known about the ecological health of Tauranga
Harbour from a western science perspective. A separate report is planned to provide a cultural
perspective based on mātauranga Maori.
Together, the two reports form a scoping exercise to summarise what is known about the
health of the harbour, in order to identify the main information gaps and priorities for field
research in Tauranga Harbour. This will help both to understand better the causes of the
decline in the harbour’s ecological health and to develop strategies for restoration.
This report is based on information that has been collected and published by other scientists
and agencies. Detailed information from those previous studies has been included here where
it has particular relevance for Tauranga Harbour, but readers interested in research methods
and other detail from those studies should refer to the source material.
1.2. The Manaaki Taha Moana project
This report is one in a series of reports and other outputs from the research programme
“Enhancing Coastal Ecosystems for Iwi: Manaaki Taha Moana” (MAUX0907), funded by the
Ministry for Science and Innovation (previously known as the Foundation for Research
Science and Technology, and the Ministry of Research, Science and Technology).
1.2.1. Study areas and personnel
Manaaki Taha Moana (MTM) is a six-year programme, running from October 2009 to
September 2015, with research being conducted primarily in two areas: Tauranga moana and
the Horowhenua coast. This programme builds upon Massey University's previous research
with Ngāti Raukawa in the lower North Island: “Ecosystem Services Benefits in Terrestrial
Ecosystems for iwi” (MAUX0502).
Professor Murray Patterson of Massey University is the Science Leader of MTM. A number of
different organisations are contracted to deliver the research: Waka Taiao Ltd with support of
Manaaki Taiao Trust in the Tauranga moana case study; Te Reo a Taiao Ngāti Raukawa
Environmental Resource Unit (Taiao Raukawa) and Dr Huhana Smith in the Horowhenua
coast case study; WakaDigital Ltd; Cawthron Institute; and Massey University. The research
team seeks to engage with local communities and end users through a variety of means.
Readers are encouraged to visit the MTM programme website (http://www.mtm.ac.nz) to read
more about this research programme.
Manaaki Taha Moana Report No. 1
1
1.2.2. MTM objectives
The central research question is: “how can we best enhance and restore the value and resilience
of coastal ecosystems and their services, so that this makes a positive contribution to iwi
identity, survival and welfare in the case study regions?” Thus, our research aims to restore
and enhance coastal ecosystems and their services of importance to iwi/hapū, through a better
knowledge of these ecosystems and the degradation processes that affect them.
We are utilising both western science and mātauranga Māori knowledge to assist iwi/hapū to
evaluate and define preferred options for enhancing/restoring coastal ecosystems. This
evaluation of options will also be assisted by the development of innovative Information
Technology and decision support tools (such as, for example, simulation modelling, interactive
mapping, 3D depiction, real-time monitoring) by WakaDigital Ltd. Action Plans will be
produced for improving coastal ecosystems in each rohe.
The research team works closely with iwi/hapū in the case study regions to develop tools and
approaches to facilitate the uptake of this knowledge and its practical implementation.
Mechanisms will also be put in place to facilitate uptake amongst other iwi throughout New
Zealand. The key features of this research are that it is: cross-cultural, interdisciplinary,
applied/problem solving, technologically innovative, and integrates the ecological,
environmental, cultural and social factors associated with coastal restoration.
Manaaki Taha Moana has three specific research objectives:
* Objective 1: Develop a Knowledge Base of Coastal Ecosystems and their Services
in the two case study regions.
This objective is focussed on determining the extent of critical coastal ecosystems and their
services in both of our case study regions (Tauranga moana and the Horowhenua coast). The
relevant research questions are: What are they? Where do they occur? How can they be
measured in biophysical, cultural and other terms? How culturally significant are they? How
much are they worth or valued?
* Objective 2: Determine how to Enhance and Restore Specified Coastal Ecosystems
and their Services in the case study regions.
We are working directly with WakaTaiao, Taiao Raukawa and other agencies in the local
communities to harness and build on the knowledge from Objective 1 to answer the central
research question of: “how can we best enhance and restore the value and resilience of coastal
ecosystems and their services, so that this makes a positive contribution to iwi identity,
survival and welfare in the case study regions?” This will be achieved through detailed case
studies in both regions, on topics of most importance to local iwi and hapū in ascertaining how
to go about restoring coastal ecosystems and their services. We will work in with other groups
and local councils who may also be undertaking complementary-focussed research.
2
Manaaki Taha Moana Report No. 1
* Objective 3: Implementation and Benefit Transfer to other Iwi.
A condition of involvement of both Tauranga moana iwi and Ngāti Raukawa in this research
programme is that the research be implemented to bring about real change in the state of
coastal ecosystems in their rohe. Both Tauranga moana iwi and Ngāti Raukawa have
catalogued the poor state of many coastal ecosystems in their rohe - recalling, for example,
accounts from tribal elders of the abundant kaimoana found 40 to 50 years, but not today.
Both iwi groups are committed to arresting these trends and keen, through this research
programme, to put in place Action Plans and other mechanisms to improve the quality of the
coastal environment. Further, the tools and frameworks developed in this project will be made
available to iwi and other end user groups nationally through information and communication
technology and other means.
1.2.3. Fit with other MTM work
The initial research activities for this first phase of MTM have focussed on Objective 1,
‘Building Up a Knowledge Base of Coastal Ecosystems and their Services’, in both case study
regions. In summary, we have been engaged in an ecological stocktake of “what is already
known” about the state of coastal ecosystems in each rohe including both mātauranga Māori
and western science knowledge; creating a mediated model of Tauranga Harbour and the interrelationships between the various factors that contribute to its health; and the development of
initial information technology tools to help us capture and utilise this critical knowledge and
information to bring about restoration to coastal ecosystems. Collectively, these components
will help inform the research team and tangata whenua in the selection case studies for more
in-depth study and tool development in subsequent stages of MTM.
Thus, this initial “stocktake” phase has involved a number of inter-related components:
an ecological ‘stocktake’ of the Tauranga moana and Horowhenua coast (from the Hokio
Stream to Waitohu Stream). The purpose of this ecological stocktake was to summarise all
information on the past and current state of the ecological health of the Tauranga Harbour and
the Horowhenua coast case study regions. This stocktake was undertaken to provide a basis
for selecting our case studies for Objective 2, and is also a mechanism to communicate our
assessment of the ecological health of the respective coasts to our stakeholders. The results of
this ‘ecological stocktake’ will be made available in two main formats – written reports (such
as this report for Tauranga Harbour and a report on the ecological and cultural health of the
Horowhenua coastal area), and a searchable on-line data repository on the MTM website that
anyone can use to discover what information exists about the state of coastal ecosystems in the
case study regions.
For the Tauranga moana case study, a mātauranga Māori interpretation of the coastal
ecosystems will be published to complement this report. We hope to work on the integration
of the Māori knowledge with the information contained in this report, which is predominantly
based on western science. In the MTM programme, we endeavour to find appropriate ways of
utilising both mātauranga Māori and western science to solve ecological problems in the case
study regions, hence the importance of having a robust mātauranga Māori research framework.
Manaaki Taha Moana Report No. 1
3
Mediated Modelling of the Tauranga Harbour. Mediated modelling is a tool whereby
stakeholders can be involved in the model development and eventually use the model to
identify and solve problems. We have initiated a study on Tauranga moana, which will be one
of the first applications of ‘mediated modelling’ in a cross-cultural research programme
anywhere in the world. The primary purpose of mediated modelling is to understand the
dynamics of the harbour in a ‘holistic’ and ‘integrated’ way with an eye to assisting the
selection of case studies for Years 2-6 of MTM. More information can be found on our
website: http://www.mtm.ac.nz/mediated-modelling/.
Information Technology (IT) tools. One of the key aspects of MTM is the development
of IT tools to better communicate research results and to support decision-making by iwi/hapū
end-users and other stakeholders. This IT development is being undertaken and led by
WakaDigital Ltd, in conjunction with the other partners in MTM. The initial focus has been
on developing:
a web-based central information repository (our Digital Library can be accessed
online at http://www.mtm.ac.nz/client/knowledge_centre-digital_library.php);
a communication portal/website for the research team and iwi/hapū end-users, and
updating the efish database to include new data.
Future IT development is likely to involve simulation modelling (what would happen in 20-30
years if we implemented ‘xyz’ management option), interactive mapping, and 3D depiction
(where are the problems occurring). One of the objectives of using these IT tools is to critically
assess their efficacy and appropriateness in the context of Māori-focussed research.
1.2.4. Next steps
The present stocktakes are helping to inform our research team about what knowledge gaps
exist regarding the state of the coastal ecosystems and their services in our case study areas,
and what the most critical areas are for ongoing investigation. In close collaboration with local
tangata whenua, we will shortly select and begin detailed case study research in both Tauranga
moana and the Horowhenua coast. Further reports will be produced on these case studies.
1.3. Outline of this report
This report describes the health of Tauranga Harbour from the bottom up, that is, starting with
the land and history of its development (chapter 2), then the water and impacts upon it (chapter
3).
Chapter 4 reviews what is know about the flora and fauna of the harbour, starting at the bottom
of the food web with phytoplankton and macroalgae, moving up to the fish and eventually the
marine mammals. In chapter 5, we conclude by identifying gaps in our understanding about
Tauranga Harbour and outlining some potential research to address these during this project.
4
Manaaki Taha Moana Report No. 1
2.
DESCRIPTION OF THE HARBOUR
2.1. Location and hydrodynamics
Tauranga Harbour, or Te Awanui, is a large estuary (approximately 200 km2) located on the
western edge of the Bay of Plenty on New Zealand’s North Island (37° 40’S. 176° 10’E)
(Inglis et al., 2008). The harbour is protected from the Pacific Ocean by a barrier island
(Matakana Island) and two barrier tombolos, Bowentown at the northern entrance and Mount
Maunganui to the south (Figure 1).
Two harbour basins are separated by large intertidal flats in the central area of the harbour. At
mean high water the Katikati (northern) basin has an approximate volume of 178 million m3
and the Tauranga (southern) basin a volume of 278 million m3 (Park, 2009). While the two
basins are connected there is little water exchange between the two (Barnett, 1985; de Lange,
1988). Some reports mention a third smaller basin that includes several bays and subestuaries(Park, 2003); this most likely refers to the estuarine area to the south of the Port of
Tauranga.
The two main entrances to the harbour are at either end of Matakana Island where the tide
flows strongly through both channels (Figure 1). Tidal flow generates up to four knots at the
south eastern Tauranga entrance and up to seven knots at the north western Katikati entrance
(Ellis et al., 2008). Both harbour entrances are approximately 800 m across, with tidal scour
ensuring that deep channels are maintained (Inglis et al., 2008). The rest of the harbour is
shallow, typically less than 10 m deep, with intertidal flats comprising approximately 66% of
its total area (Inglis et al., 2008). Tidal currents and wind-generated waves dominate the
hydrodynamics of the harbour (Davies-Colley and Healy, 1978). Tidal flows have a residence
time ranging from a few hours up to a month (Heath, 1976).
The Port of Tauranga, established in 1873, is located near Mount Maunganui at the
southeastern end of the harbour (Inglis et al., 2008; Thompson, 1981). Dredging occurred
from 1968 to 1978, and again in 1991 to 1992, to deepen and widen shipping channels and
reclaim land to establish a container terminal. Since 1992, maintenance dredging has been
regularly required to maintain adequate channel depths (Healy et al., 1991).
Manaaki Taha Moana Report No. 1
5
N
Bowentown Heads
Katik
ati E
ntra
n
ce
Katikati Basin
(Northern Basin)
Bay of Plenty
Matahui Point
Matakana Island
Matakana Point
ra
Tau
nga
Tauranga Basin
(Southern Basin)
e
nc
tra
En
Mount Manganui
Port of Tauranga
Tauranga City
0
Figure 1.
6
2.5
5
10 km
Tauranga Harbour showing the dividing line between the northern and southern basins.
Inset shows the wider Bay of Plenty region.
Manaaki Taha Moana Report No. 1
2.2. The catchment area
The Tauranga Harbour catchment covers 1,300 km² and is home to an estimated 150,000
people as of 20101 (Environment Bay of Plenty, 2009b; Lawrie, 2006; Tauranga City Council,
2009a). The harbour receives discharges from many separate catchments originating in the
Kaimai-Mamaku ranges (Shaw et al., 2010) (Figure 2). The northern harbour catchments
cover an area of 270 km2 with a mean freshwater inflow of 4.1 m3s-1 while the southern
harbour catchments cover 1,030 km2 and have a mean freshwater inflow of 30.5 m3s-1 (Park,
2009). The freshwater inflow represents only 0.1% of the harbour volume per tidal cycle in
the northern basin and 0.48% in the southern basin (Park, 2003).
The Kaimai-Mamaku Ranges form the northwestern boundary to the Tauranga Harbour
catchments and were formed by a series of late Pliocene rhyolite eruptions within the
Coromandel Volcanic Zone (Shaw et al., 2010). In contrast, the plateau country in the south
(Mamaku and Whakamarama plateaus) was formed by eruptive events originating within the
Taupo Volcanic Zone, which became active during the Pliocene and remains active today
(Shaw et al., 2010). The upper Tauranga Harbour catchments (eastern side of the Kaimai and
Otanewainuku ranges) are typically steep, with streams having high fall rates, high stream
velocities and low flow volumes (Shaw et al., 2010). Catchments in the central Tauranga area
flow from ignimbrite-dominated landforms, where streams have scoured deep steep-sided
gorges into land of otherwise relatively flat relief (McIntosh, 1994; Shaw et al., 2010).
Between the upper catchments and Tauranga Harbour, the landscape is dominated by
undulating low hills formed by siltstones, sandstones, conglomerates and fluviatile sands
(Healy et al., 1974; Shaw et al., 2010). The barrier formations of the harbour were derived
from sediment eroded from ash deposits (McIntosh, 1994). Figure 3 provides a geological map
of the region.
1
Statistics New Zealand subnational population estimates tables for 30 June 2010. www.stats.govt.nz. The
combined population estimate for Tauranga City Council and Western Bay of Plenty District Council was
159,680; some of the WBOP district council area is outside the catchment of Tauranga Harbour.
Manaaki Taha Moana Report No. 1
7
Figure 2.
8
The catchments of the Kaimai-Mamaku Range. Catchments drain to Tauranga Harbour except
Waihi, Paeroa, Te Aroha, Middle and Upper Waihou, which drain to Hauraki Gulf. LUC is Land
Use Capability classification, with Class 1 the most versatile land (the least limitations for
productive use) and at the other end of the scale Class 8, which is not suitable for productive use
(most limitations). Source: (Shaw et al., 2010).
Manaaki Taha Moana Report No. 1
Figure 3.
Geological map of Tauranga and the southern Kaimai Range. Inset shows location of Coromandel
and Taupo Volcanic Zones in the North Island, New Zealand. Ma = million years ago. Source:
(Briggs et al., 2005).
Manaaki Taha Moana Report No. 1
9
As of 2008, the land cover in the Tauranga Harbour catchment was predominately pasture and
indigenous forest (Figure 4). Table 1 shows the breakdown by sub-catchment. The Wairoa
sub-catchment has the largest area, most of which is indigenous forest (57%). Otawa and
Waimapu sub-catchments show the most urbanisation (21% and 10% respectively), while the
Rereatukahia, Aongatete and Tuapiro sub-catchments have almost no urban areas (0-1%).
More than half of the Tauranga Harbour catchment area (64%) is land with limited productive
use, primarily due to erosion risk (Shaw et al., 2010); much of this is evidently in pasture
(Figure 2).
Wetlands
1%
Exotic forest
Horticulture Urban
11%
4%
7%
Grassland
39%
Indigenous forest
38%
Figure 4.
Land cover within the Tauranga Harbour catchment in 2008. Source: (Bay of Plenty Regional
Council based on LUCAS land use database from the Ministry for the Environment.)
Table 1.
Land cover in the ten sub-catchments of Tauranga Harbour
SubCatchment
Indigenous
Exotic
Orchards &
Pasture
Urban
Other
Forest
Forest
Crops
(ha)
(%)
(%)
(%)
(%)
(%)
(%)
Uretara
5336.1
37
39
3
16
4
1
Waiau
5885.3
15
49
21
6
5
4
Rereatukahia
6170.9
42
37
3
16
1
1
Tuapiro
6622.4
52
29
3
15
0
1
Te Puna
8630.5
21
54
5
16
3
2
Otawa
9862.5
18
40
13
6
21
3
Aongatete
12543.4
53
37
2
7
0
1
Waimapu
13029.4
30
47
6
5
10
2
Omanawa
17330.0
39
31
16
5
9
1
Wairoa
36930.3
57
27
12
2
9
1
Source: GIS analysis undertaken by Wildland Consultants Ltd using LCDB2 data reflecting land use in 2001/02
(Shaw et al., 2010).
10
Area
Manaaki Taha Moana Report No. 1
The Tauranga ecological district has also been surveyed to identify natural areas and assess the
values associated with those areas (Beadel et al., 2008). That report identified the size and
distribution of natural areas within the Tauranga Ecological District and recommended areas
for protection.
Tauranga Harbour and its surrounding catchments are within the boundaries of the Bay of
Plenty Regional Council (BOPRC), which has primary responsibility for resource management
issues affecting the harbour. Tauranga City Council and the Western Bay of Plenty District
Council also have resource management functions relevant to the harbour, as do the
Department of Conservation (DOC), Ministry of Fisheries (MFish), MAF Biosecurity New
Zealand, Ministry for the Environment (MfE), Maritime New Zealand, and Fish and Game
New Zealand. The functions of each of these agencies are described in Appendix 1.
2.3. Climate
The lowlands surrounding Tauranga Harbour are warm and sub-humid with a median annual
temperature of 15°C. Annual rainfall ranges from 1,125 mm yr-1 in the southeast (near
Tauranga city) to 1,700 mm yr-1 in the northwest, around Bowentown, and up to 2,500 mm yr-1
in the Kaimai-Mamaku range above the harbour (Parshotam et al., 2008). Tauranga City
receives around 2,200 to 2,400 sunshine hours annually (Tauranga City Council, 2009a).
Future climate projections for New Zealand include increasing prevalence of extreme events
such as floods, landslides and storms (IPCC, 2007). One of the most significant influences of
climate change in the Bay of Plenty is likely to be the resulting rise in sea level. Although the
documented rise over the past 100 years is slightly lower in the Bay of Plenty than the national
average (0.14 m compared with 0.16 m), the melting of the polar ice caps from rising
temperatures will accelerate sea level rise (Bell et al., 2006). With increasing sea level, more
frequent flooding of coastal margins by extreme tides, surge and waves is possible, making
lowland areas vulnerable to inundation (Dahm et al., 2005).
2.4. Settlement of the harbour
Tangata whenua have occupied the Tauranga Harbour area for generations; exactly how long
is not known. Tauranga’s attractive climate, abundant kai moana, kai awa, edible flora and
birds provided Māori with all their nutritional needs (Ellis et al., 2008). Areas were also
cultivated on a rotational basis, through a cycle of burning, then planting and cultivation for
several seasons, then leaving the land to lay fallow (Shaw et al., 2010).
A map of the Tauranga District in 1840 shows the Tauranga District (i.e. what is now
Tauranga City and Papamoa) was a mosaic of shrubland, fernland forest, estuarine vegetation
and freshwater wetlands (Wildland Consultants Ltd., 2000) (Figure 5). European settlement
on a significant scale began in Tauranga and Te Puke lowlands in the 1870s. This meant
further clearance and modification for farming, logging and mining. By 1900, much of the
Manaaki Taha Moana Report No. 1
11
forest in the Whakamarama, Kaimai and Oropi areas and south-west of Te Puke had been
cleared (Shaw et al., 2010).
Figure 5.
12
Land cover in Tauranga District in 1840 (top) and 2000 (bottom). Source: (Wildland Consultants
Ltd., 2000).
Manaaki Taha Moana Report No. 1
Towns were initially established near mission stations, partly on land confiscated from Māori
and redistributed after the New Zealand wars (Shaw et al., 2010). Tauranga grew rapidly in
the 1950s and 1960s and in 1963 was proclaimed a city, with a population of 21,500
(Environment Bay of Plenty, 1997). This urban growth led to reclamation of harbour areas
and drainage of wetlands. Additionally, there were extensive plantings of exotic forest, with
the very steep, more remote areas remaining in native bush (Environment Bay of Plenty,
1997).
The establishment of the port in 1873 made Tauranga a key entry and exit point for goods in
New Zealand, chiefly timber and timber products. More recently kiwifruit and avocados have
been another primary export, with the conversion of a significant amount of pastoral land to
horticulture (Shaw et al., 2010). The Port of Tauranga (Figure 6) is the largest port in New
Zealand in terms of total cargo tonnage, and the second largest in terms of container
throughput (Dacruz, 2006).
Figure 6.
Activity at the Port of Tauranga (photos: Noel Peterson).
Manaaki Taha Moana Report No. 1
13
3.
WETLANDS AND WATER QUALITY
3.1. Wetlands
Wetlands are important ecosystems and have functional values in water quality,
hydrology, ecology, and culture; their protection is a national priority.
Wetlands improve coastal water quality by acting as a physical and biochemical filter
to immobilize sediment and pollutants.
In the North Island only 5% of original wetland area remains intact (1997)*.
Between 1840 and 1991, palustrine (freshwater) wetland area around Tauranga
Harbour declined by 84% while estuarine wetland area in Tauranga Harbour increased
by 17%, reflecting a marked increase in mangrove vegetation (2000).
Approximately 700 ha of saltmarsh has been lost since 1840 due to land reclamation
(2000).
Changes in area of other types of estuarine wetlands, many of which provide
important habitat for birds, have not been monitored.
* Dates indicate how current the information is; full references to source documents are given in the main text.
The Ramsar Convention on Wetlands is an international treaty for the conservation and
sustainable utilisation of wetlands. The Ramsar Convention defines wetlands as “areas of
marsh, fen, peatland or water, whether natural or artificial, permanent or temporary, with
water that is static or flowing, fresh, brackish or salt, including areas of marine water the
depth of which at low tide does not exceed six metres" (Ramsar Convention Secretariat, 2006).
In a New Zealand context, the Resource Management Act 1991 (RMA) defines wetlands as
“permanently or intermittently wet areas, shallow water or land/water margins that support a
natural ecosystem of plants and animals that are adapted to living in wet conditions”
(Clarkson et al., 2003).
For the purpose of this report, ‘wetlands’ refers to wetland ecosystems with both ‘marine’ and
‘estuarine’ hydrosystems, as well as ‘palustrine’ (freshwater) hydrosystems, as defined by
Johnson and Gerbeaux (2004). Freshwater wetlands, although by definition not part of
estuaries, are thought to contribute significantly to the quality of receiving waters in the
surrounding catchment and thus can have an important influence on ecosystems in Tauranga
Harbour. Estuarine wetlands are defined as per Park (2000b) and include saltmarsh, algal flats,
mudflats (including mangroves) and sandflats, but not seagrass meadows, which are discussed
separately in section 4.1.3.
General observations can be made regarding the ecological, cultural, and social value of New
Zealand wetlands and how they are managed before considering information on wetland areas
specific to Tauranga Harbour.
The wetlands of New Zealand have always been an important part of the New Zealand
environment. The earliest Māori settled around coastal estuaries and lagoons and harvested
the shellfish, fish and eels that abounded. It was from the flax swamps that material for
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Manaaki Taha Moana Report No. 1
weaving was collected and waterfowl snared. To the early Pakeha, wetlands brought an export
product - flax fibre stronger than any fibre yet in use in the world.
Clarkson et al. (1999) notes that wetlands are among the most important ecosystems on the
planet and have values for their functions in water quality, hydrology, ecology, and for culture.
Wetlands improve coastal water quality by acting as a physical and biochemical filter to
immobilize sediment and pollutants that pass through them. They act as buffers against
flooding during storm events and release water slowly back into the ground. Some wetlands
can also recharge and discharge to groundwater depending on local hydrological conditions.
Ecologically, wetlands are important natural systems for supporting aquatic and terrestrial
organisms. They can be highly productive systems (MfE, 1997). Wetlands have been
identified as a national priority for the protection of biodiversity and are included in the
proposed national policy statement on indigenous biodiversity2 released in January 2011.
Since European settlement, New Zealand wetlands have been greatly reduced. The enormous
flat swamplands yielded fertile soil when drained, sustaining farmers and supporting sheep and
dairy cows. Drainage became a major cultural activity, like bush clearance, a symbol of the
"great work" of turning New Zealand into an economically productive land (Commission for
the Environment, 1986). Only about 10% of original wetlands remain nationally, whilst in the
North Island only 5% of original wetlands are still intact (MfE, 2007). As a result, these
wetlands support a disproportionately high number of New Zealand’s threatened plants and
animals (Clarkson et al., 2003).
Wetlands are often found associated with the margins of rivers, lakes and estuaries and form a
boundary zone between land and water. They may therefore be an integral part of the water
body and its aquatic ecosystem, as well as the land and its terrestrial ecosystems (MfE, 1997).
It is, therefore, important that they are not drained or otherwise damaged (Environment Bay of
Plenty Regional Council, 2003).
3.1.1. Bay of Plenty wetlands
Wetlands are particularly vulnerable to the adverse effects of land use and development. The
Bay of Plenty Regional Water and Land Plan (Environment Bay of Plenty, 2008) covers
natural and physical resources in the Bay of Plenty and includes wetlands as a water body.
Issues identified in the plan include; loss of freshwater wetlands; lack of community
understanding of the scarcity, value and vulnerability of wetlands; threat from adverse effects
of development; and artificial maintenance of water levels. Responsibility for the management
of wetlands rests with multiple agencies. BOPRC and Territorial Authorities have an
advocacy role and are responsible for the control of activities in wetlands (Environment Bay of
Plenty, 2008).
2
http://www.mfe.govt.nz/publications/biodiversity/indigenous-biodiversity/proposed-national-policystatement/statement.pdf
Manaaki Taha Moana Report No. 1
15
The loss of wetlands as a result of sea level rise is of concern to BOPRC (Lawrie, 2006),
particularly in areas where there is little space between urban development and the harbour.
These wetlands are likely to be “squeezed” further, resulting in loss from infilling around
harbour margins and loss due to drainage. Loss from drainage includes direct drainage and
drying of wetland areas, as well as loss from the interception and diversion of ground water
flows. This is thought to lead to increased salinity which causes degradation/loss of wetland
condition, and is often associated with weed invasion.
A report by Park (2000b) on the Bay of Plenty Maritime Wetlands Database draws on data
collected from wetland vegetation surveys, digital mapping, database design, and data capture
for nearly all the maritime wetland within the Bay of Plenty region. In addition, an estimation
of historic wetland area has been mapped using aerial photography for Tauranga and Ohiwa
Harbours. The surveys and data can provide both spatial and quality assessments for areas of
special importance as well as baseline data to enable assessment, monitoring and evaluation of
environmental programmes. Park (2000b) presented only an initial analysis of the information
contained in the database to display its usefulness for environmental management, and noted
there was a great deal more analysis possible.
BOPRC subsequently commissioned Wildland Consultants to digitise the external boundaries
of freshwater wetlands in the Bay of Plenty Region. The desktop mapping exercise excludes
wetlands influenced by saline water such as saltmarsh, and notes the questionable accuracy for
many sites, especially those in close proximity to coastal margins where the boundary was
difficult to determine.
The loss of wetland in the Bay of Plenty area has given rise to community efforts to restore
and rehabilitate wetland areas. The Wetland Restoration Guide (Bay of Plenty Wetlands
Forum, 2007) provides an overview of methods for creating or restoring a wetland, looking
specifically at wetland types and characteristics within the Bay of Plenty.
3.1.2. Wetlands in Tauranga Harbour
According to Cromarty and Scott (1995), Tauranga Harbour is one of New Zealand's largest
estuaries, with extensive, largely unmodified, intertidal seagrass beds, tidal flats, mangroves
and mixed saltmarshes. Cromarty and Scott (1995) provide a comprehensive overview of
Tauranga Harbour as a wetland system, including their state and management.
Natural areas within Tauranga Harbour have also been surveyed by Wildland Consultants
(Beadel et al., 2008) providing information on both terrestrial and estuarine wetlands.
Terrestrial natural areas were found to total 3,316 ha, 4.9% of the terrestrial area, with a heavy
bias toward dune vegetation (814 ha) and wetlands (1,102 ha) within the coastal zone,
particularly Matakana Island. In total 168 natural areas comprising 24,284 ha of saltmarsh,
mangroves, intertidal, estuarine, subtidal and harbour habitats were identified. The largest
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Manaaki Taha Moana Report No. 1
natural areas identified were those associated with marine environments which, together with
all marine and estuarine areas, comprise 24.5% of the area of the Tauranga ecological district.
In contrast, terrestrial natural areas occupied 3.7% of the area of the ecological district. The
Wildlands report (Beadel et al., 2008) provides an overview of the extent of natural areas
within the Tauranga ecological district in each vegetation class (e.g. primary forest, secondary
forest, indigenous wetland, estuarine saltmarsh, estuarine mangrove etc) for coastal and semicostal zones.
Park (2000b) provides a useful analysis of temporal change to wetland extent in Tauranga
Harbour. The analysis indicated that between 1840 and 1991, palustrine wetland area reduced
by 84%, and estuarine wetland area increased by 17%. The increase in estuarine wetland is
indicative of a marked (possibly exponential) increase in the area of mangroves, and is likely
caused by increased sediment input. The report concludes that the most significant loss of
estuarine wetland in Tauranga Harbour is through land reclamation for agricultural use. It is
estimated that approximately 700 ha of saltmarsh has been lost in this way since 1840, which
accounts for approximately 30% of this type of habitat across the Bay of Plenty region.
According to Park, some of this area can be rehabilitated, but most cannot.
The rise of community care groups around Tauranga Harbour, especially around estuaries and
waterways, highlights the community concern for degraded natural environments. Many care
groups take a broad catchment approach to managing local environments, and work hard in
building rapport and relationships with local landowners in an effort to improve environments.
Restoration of harbour margins, esplanade reserves, and wetland systems are an integral part of
care group functions.
Tangata whenua also take an active role in managing their environments, either directly by
partnering with local care groups, or indirectly by developing their own resource management
plans. The Te Awanui Tauranga Harbour Iwi Management Plan (Ellis et al., 2008) is a
cooperative planning document prepared by the three iwi of Tauranga moana in response to
the poor health of the harbour. This Plan recognizes the importance of wetland systems as
specialised ecological and cultural areas. Tangata whenua consider wetlands and the
associated flora, fauna and aquatic species as taonga. Wetlands are important cultural spaces,
supplying traditional foods, and textiles. Spring fed wetlands were also an important water
supply source. Many wetlands around the harbour margins contain sacred burial sites and are
considered tapu. These areas are afforded the utmost protection by tangata whenua as the final
resting place of their ancestors (Ellis et al., 2008; Fisher et al., 1997).
Manaaki Taha Moana Report No. 1
17
3.2. Sedimentation
Land in pasture makes the largest contribution to the sediment load in the southern
Tauranga Harbour (63% of total) (2010).
57% of sediment generated in the catchment enters the harbour (2010).
Of this land-derived fine sediment, 42% flows out to sea (2010).
The sub-estuaries in the southern half of the harbour receiving the most deposition are
Te Puna inner, the mouth of the Waipapa River and Mangawhai Bay inner (2010).
Sediment accumulation rates on exposed intertidal flats are low compared to other
North Island estuaries (2009).
Climate models project a 48% increase in mean annual sediment load to the southern
harbour by 2051, and a 94% increase for one area (2010).
Sedimentation affects many aspects of harbour ecology.
The Port of Tauranga carries out dredging to maintain the channel for shipping
activity.
3.2.1. Sediment inputs to the harbour
Tauranga Harbour was likely a shallow embayment when it originally formed (Hume and
Swales, 2003) and has since filled in with sediment derived from the land and coast to form the
extensive intertidal flats that are present today. Land derived sediments are delivered via
rivers and tend to be muddy while coastal sediments enter the harbour through tidal action and
tend to be sandy. Lawrie (Lawrie, 2006) estimated that almost 120,000 tonnes of sediment
wash into the harbour each year, mostly from farmland and forested areas via rivers and
streams. A recent study estimated the sedimentation from the southern harbour alone at
108,000 tonnes per year, suggesting the total amount entering the harbour is even higher
(Elliott et al., 2010).
Sediment yield into the marine environment depends primarily on land slope, soil type, rainfall
and land use with highest loss from land in pasture, steep slopes and soils that are less welldrained (Elliott et al., 2010). Elliott et al. (2010) modeled sediment loading to the southern
Tauranga Harbour from the surrounding catchment (Table 2) and found that pasture (34% of
the catchment) makes the largest contribution to the sediment load (63% of total), with
forested areas contributing 27%. Although forest has lower sediment yields than pasture (1.2
versus 3.6 t ha-1 y-1), it covers a larger portion of the catchment (44%) and tends to be located
in steep areas with high rainfall. Orchards and cropland (5% cover) make only a small
contribution to the load (0.3%) as they tend to occur on land less prone to erosion.
Uncontrolled earthworks have the highest sediment yield but controlled earthworks have a
much lower yield and overall earthworks contribute only 0.5% to the total sediment load.
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Table 2.
Sediment load and sediment yield to the southern Tauranga Harbour from various land uses.
These values are before sediment deposition in the stream network. The yields in this table are
averaged over the range of slopes, soils and climate that occur.
Land use
Pasture
Bush, scrub, native forest
Exotic forest
Other bare earth
Urban earthworks
Urban and roads
Orchard and cropland
Source: (Elliott et al., 2010)
Total load
(t yr-1)
119696
52291
9079
3227
992
2162
579
Fraction of
total load (%)
62.5
27.3
4.7
3.5
0.5
1.1
0.3
Total
area (ha)
33262
43595
10098
121
186
6416
4963
Fraction of
total area (%)
33.7
43.9
10.2
0.1
0.2
6.5
5.0
Yield
(t ha-1 yr-1)
3.60
1.20
0.90
26.66
5.33
0.34
0.12
The sediment load delivered from a catchment system tends to increase with the area of the
catchment (Elliott et al., 2010). The largest sub-catchment (Wairoa) produces most of the
sediment to the southern harbour (46% of total load) (Table 3; Figure 7). The Apata subcatchment has the highest yield (2.4 t ha-1 y-1), due to the relatively high rainfall in conjunction
with pasture land use and moderate slopes. Matakana 1 sub-catchment has the lowest yield
(0.04 t ha-1 y-1), as a result of land use dominated by pine forest and well-drained soils. Urban
catchments had relatively low yields as a result of low sediment concentrations from
impervious areas. Overall, 57% of sediment generated in the catchment reaches the estuary
(Table 3).
Table 3.
Sediment load to the southern Tauranga Harbour, with yield and sediment delivery ratio (SDR) for
each sub-catchment. Yield is the load from the sub-catchment to the estuary divided by the subcatchment area; SDR is the percentage of sediment generated that actually reaches the harbour (the
rest remains in the stream network).
Sub-catchment
Area
name
(ha)
Wairoa
46534
Waimapu
11824
Kopurererua
7879
Aongatete Bellevue
7854
Waitao
4332
Waipapa
3680
Wainui
3523
Te Puna
2799
Kaitemako
1989
Matakana 1
1409
Mt Maunganui
1299
Apata
1240
Papamoa
1182
Oturu
1158
Mangawhai
957
Bellevue
950
Matakana 2
755
Total
99366
Source: (Elliott et al., 2010)
Manaaki Taha Moana Report No. 1
Load
(t y-1)
49641
16262
8113
4717
8078
4722
4891
4274
2045
62
393
2955
318
453
1251
267
316
108758
Fraction of total
load (%)
45.6
15
7.5
4.3
7.4
4.3
4.5
3.9
1.9
0.1
0.4
2.7
0.3
0.4
1.2
0.2
0.3
100
Yield
(t ha-1 y-1)
1.07
1.38
1.03
0.6
1.86
1.28
1.39
1.53
1.03
0.04
0.3
2.38
0.27
0.39
1.31
0.28
0.42
1.09
SDR
(%)
54
61
60
50
64
55
54
57
66
85
83
67
59
60
75
80
87
57
19
Figure 7.
Approximate location of sub-catchments in the southern Tauranga Harbour as defined by Hume et
al. 2010. Inset shows wider Tauranga Harbour. Note that for some sub-catchments, only part of
the sub-catchment area is shown.
Coastal sediments also play a role in the harbour as sediment is transported down the coast and
into the harbour by a process known as littoral drift. Approximately 22,000 m3 yr-1 of
sediment from littoral drift passes the harbour entrance from the north (Kruger and Healy,
2006); it is unclear how much of this sediment enters the harbour and how much is deposited
versus washed out on the outgoing tide. Maintenance dredging removes an annual average of
110,500 m3 of sediment from the harbour entrance, to maintain the channel at a navigable
depth of 14 m (Kruger and Healy, 2006).
3.2.2. Dynamics
Once in the estuary, sediment is entrained and transported by wave action and tidal currents.
Currently about 42% of the land-derived fine sediment into the southern harbour is lost to the
ocean, with some areas of the harbour tending to be more depositional (as little as 15% net
loss) than others (up to 87% net loss); see Table 4 and Figure 8 (Hume et al., 2010).
Compared to fine sediments, a much higher percentage of coarse sediments remains within the
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harbour because they are heavier and therefore less easily re-suspended by waves and currents
(Green, 2010).
Table 4.
Annual mean fine sediment sedimentation rate, loss of fine sediment to the ocean, mud content of
sediment and mean grain size for sub-estuaries in the southern Tauranga Harbour.
Sub-estuary
Speedway
Rangataua Bay
Welcome Bay
Waimapu
Tauranga City Foreshore
Waipu Bay
Waikareao
Mouth of Wairoa River
Waikaraka
Te Puna (outer)
Mangawhai Bay (outer)
Mouth of Waipapa River
Pahoia Beach Rd
Mouth of Wainui River
Aongatete
Mid Harbour Sandbanks
Matakana Island
Rangiwaea Island
Hunter’s Creek
Mangawhai Bay (inner)
Oikimoki Point
Sandbank
- E. of Motuhoa Is
- W. of Omokoroa Penin
- E. of Omokoroa Penin
Matua
Te Puna (inner)
Source: (Hume et al., 2010)
Manaaki Taha Moana Report No. 1
Mean fine
sedimentation
rate (mm y-1)
1.48
0.50
2.11
1.15
0.0
0.22
1.01
0.0
0.77
0.71
0.25
2.67
2.38
2.36
1.63
0.0
0.0
0.06
0.15
2.55
0.0
Loss of fine
sediment to ocean
(%)
15
67
23
81
n/a
87
80
n/a
26
26
41
53
41
32
40
42
42
41
-
Mud
content
(%)
14
6.9
31.4
30.3
9.8
8.1
20.8
3.5
35.7
22.3
23.7
6.3
48.1
43.7
27.1
14.4
3.4
10.8
8.5
4.4
Mean grain
size
(mm)
0.27
0.32
0.27
0.34
0.40
0.32
0.16
0.30
0.27
0.28
0.19
n/a
0.06
0.18
0.40
0.32
0.32
0.24
0.0
0.0
0.0
0.6
6.51
53
64
26
0.7
4.3
14.1
10.8
-
0.24
0.31
0.33
0.29
-
21
Figure 8.
Approximate location of sub-estuaries in the southern Tauranga Harbour as defined by Hume et al.
2010. Grey shading shows deep channels within the harbour and inset shows the wider Tauranga
Harbour. The location of Bluegum Bay is also identified.
The deposition of sediments depends on grain size and harbour morphology. In areas of
higher wave energy, such as the central harbour, sediments tend to be sandy with larger grain
size because only the heavier particles drop out of suspension. Finer sediments are carried to
lower energy environments, such as embayments and harbour margins (Green, 2010). Park
(2003) identified the Wainui/Apata estuary (Mouth of the Wainui River and Pahoia Beach
Road sites) as one of the muddiest areas of the harbour (55-70% mud content) and Bluegum
Bay one of the sandiest (5% mud content). A second study, focusing on the southern part of
the harbour and drawing from 10 data sets ranging from 1979 to 2008, also noted the Mouth of
the Wainui River and Pahoia Beach Road sites as having the muddiest sediments (43-48%
mud content) (Hancock et al., 2009) (Table 4). This study did not include Bluegum Bay and
instead identified the sandbank east of Motuhoa Island as the sandiest area (0.7% mud
content). The mean grain size in the harbour ranges from 0.06 to 0.40 mm (Hancock et al.,
2009) (Table 4).
The most depositional sub-estuaries in the southern harbour are: Te Puna inner (6.51 mm y-1
net accumulation, 26% sediment from the adjacent catchment is lost to the ocean); the mouth
of Waipapa River (2.67 mm y-1, 53% loss); Mangawhai Bay inner (2.55 mm y-1, 41% loss)
(Hume et al., 2010). The central reaches of the southern harbour and the intertidal flats along
the Tauranga City foreshore are too exposed to accumulate fine sediments. Detailed
radioisotopic dating showed sediment accumulation rates on intertidal flats in southern harbour
sub-estuaries ranged from 0.75 to 1.57 mm yr-1 over periods of 23 to 90 years (Hancock et al.,
2009). This is a relatively low rate in comparison to the rates of accumulation reported for a
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Manaaki Taha Moana Report No. 1
number of other North Island estuaries where similar methods have been applied. Auckland
east coast estuaries averaged an intertidal accumulation rate of 4.7 mm yr-1 and the Firth of
Thames averaged 25 mm yr-1 (Hancock et al., 2009).
The low rate of sediment accumulation and evidence of deep mixing within the surface
sediments indicates a high energy environment and suggests that the large wave exposed areas
of the intertidal flat in southern Tauranga Harbour are not a long term sink for fine sediment.
These sediments may instead be deposited in sheltered bays, mangroves, salt marshes, tidal
flats and tidal creeks (Hancock et al., 2009).
3.2.3. Future predictions
Climate models indicate that the Tauranga climate is expected to get wetter with higher mean
annual rainfall (4.4% increase) and more frequent high rainfall events (Elliott et al., 2010).
With higher rainfall the net amount of sediment delivered by the river catchments into the
southern Tauranga Harbour is projected to increase substantially. Given the wettest
predictions and a medium greenhouse gas emissions scenario (IPCC scenario A1B), a 43%
increase in the mean annual sediment load delivered to the southern harbour is expected by
2051 with the majority of sediment delivery attributable to increased high rainfall events
(Elliott et al., 2010). The projected increase in mean annual sedimentation load is even larger
in many sheltered estuaries (e.g. Bellevue 94%, Matakana 1 48%, Waitao 47%). The resulting
shallowing of estuaries would be partially offset by sea level rise which may deepen estuaries
by approximately 2mm yr-1 and flood low lying coastal margins (Hume and Swales, 2003).
Future urbanization is predicted to reduce the total sediment load to the southern Tauranga
Harbour by 0.7% by 2051 (Elliott et al., 2010), offsetting a small portion of the increase
expected from climate change. This reduction in sediment load is primarily due to the
conversion of pasture to urban areas, which have a lower sediment yield (Elliott et al., 2010).
A model developed by Green (2009) will enable estimation of changes in sedimentation in
different parts of the southern harbour over time and the expected changes in harbour
morphology. The model currently hind casts zero fine-sediment sedimentation in the central
reaches of the southern harbour, including the mouth of the Wairoa River. However coarsesediment is hind cast to accumulate in this region, which is the principal coarse-sediment
depositional lobe of the Wairoa River. Fine-sediment sedimentation in the four northernmost
sub-estuaries in the model is consistent with measured sedimentation.
3.2.4. Impact on flora and fauna
Morrison et al. (2009) provide a good review of the many ways that sedimentation affects
harbour ecology. Sedimentation makes sheltered estuaries muddier and shallower, with
associated reductions in water clarity. Direct impacts include clogging of the gills of filter
feeders and decreases in the filtering efficiencies of such species (e.g. cockles, pipi, scallops),
Manaaki Taha Moana Report No. 1
23
reductions in the settlement success and survival of larval and juvenile phases (e.g. paua, kina),
reductions in the foraging abilities of finfish (e.g. juvenile snapper) and smothering of seagrass
beds (Jones, 2008; Morrison et al., 2009). There is some evidence that bivalves (such as
cockles and pipi) may be particularly sensitive to repeated exposure to high levels of
suspended sediment (Norkko et al., 2006). Estuarine animals are generally adapted to
changeable conditions, and tolerate some sedimentation. However, research has shown that
deposition of sediment as thin as three mm can change the benthic community structure
(Lohrer et al., 2004), and deposition of two cm of sediment can kill all benthic animals present
due to lack of oxygen (Thrush et al., 2004).
Sedimentation can change sediment particle size, most often resulting in greater percentage
mud in the sediment, affecting communities living within or upon the seabed. Many species
have strict sediment particle size preferences while others are susceptible to small changes in
the rate of sediment accumulation and level of turbidity (Gibberd and Carter, 2003). An
increase in mud content can lead to a decrease in burrowing animals, such as marine worms,
which are important in oxygenating the sediment and breaking down organic matter (Jones,
2008). A decrease in their abundance can alter sediment chemistry and decrease the
productivity of the entire estuary.
Indirect effects of sedimentation include the modification of ecologically important habitats,
especially those composed of habitat forming species such as seagrass beds, green-lipped and
horse mussel beds, bryozoan and tubeworm mounds, kelp forests and sponge gardens
(Morrison et al., 2009). Seagrass is particularly vulnerable to greater suspended sediment
concentrations as it has relatively high light requirements (Turner and Riddle, 2001).
Mangroves, on the other hand, respond favourably to increased sedimentation because
accumulating sediment raises the intertidal flat allowing mangroves to colonise areas that were
once too frequently inundated by the tide (Jones, 2008). Once established, mangroves trap
more sediment creating a positive feedback as suitable area for mangrove colonisation expands
(Hume et al., 2010).
An example from Northland shows that losses of important habitats, such as seagrass and
horse mussel beds, can have far reaching consequences for fish populations. Recent otolith
chemistry work has shown that west coast North Island snapper (Pagrus auratus) populations,
from Cape Reinga to Wellington, primarily originate from the Kaipara Harbour where horse
mussel beds and seagrass meadows provide nursery habitats (Morrison et al., 2009). The
Kaipara Harbour has been impacted by land use changes over the last 100 years and these
habitats continue to be affected by pressures such as sedimentation from the surrounding
catchment (Morrison et al., 2009). The carrying capacity of this system, which supports the
west coast snapper population, has declined substantially and any negative impacts on the
production of juvenile fish in this area will cascade through into the much larger coastal
ecosystem, ultimately affecting the abundance of fish several hundreds of kilometres away
(Morrison et al., 2009). Seagrass meadows were once present in the Manukau Harbour, as
described by (Morton and Miller, 1973). Historically this estuary most likely played a more
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Manaaki Taha Moana Report No. 1
important role in the contribution of snapper to the coastal population than the < 2% it
provides at present (Morrison et al., 2009).
Changes in community structure caused by sedimentation can have cascading effects
throughout the ecosystem. Benthic species are important prey for larger predators and have
important roles in maintaining water quality by cycling nutrients and stabilising sediments.
Plant communities are also integral to maintaining water quality and provide nursery grounds
for many species. Mangrove expansion may reduce intertidal mud flats, potentially reducing
wading birds’ feeding habitat (Jones, 2008).
3.2.5. Dredging activity
Currents within the harbour trap sediment in the channel entrance such that the channel is
infilling (Kruger and Healy, 2006). The Port of Tauranga carries out maintenance dredging
approximately every two years removing around 300,000 m3 of sediment each time (Inglis et
al., 2008). Around 80,000 to 100,000 m3 is extracted ashore and sold to concrete plants and
other buyers while the remaining material is deposited at seven different sites (Inglis et al.,
2008). Sand is deposited in nearshore sites to allow for renourishment of the Mt Maunganui
ocean beaches while silt and other sediment unsuitable for nearshore dumping is deposited in
offshore dump grounds (Inglis et al., 2008). Resource consent has recently been granted to the
Port of Tauranga for further dredging (Hill et al., 2010). This consent has been appealed and
was heard in the Environment Court in April 2011; a decision is pending (S. Park, pers.
comm.).
3.3. Nutrients
Many streams entering the harbour have elevated nutrient levels, with many sites at
levels that support undesirable biological growth (2011).
Levels of nutrients (N and P) within the harbour are declining (2005).
Decreasing nutrient trends in some rivers are linked with improved rural practises,
better control of surface runoff and land use changes (2009).
Increasing nutrient trends in other rivers are associated with agriculture and
increasing runoff from recently harvested forest (2009).
Omanawa, Kopurererua, Waimapu and Rocky streams had elevated nitrogen
concentrations (2009).
Phosphorus levels were highest in the Rocky and Kopurererua streams (2009).
Under most conditions, the availability of nitrogen and phosphorus is the limiting factor for
primary production (Nybakken and Bertness, 2005). Coastal waters receive nutrient inputs
from adjacent land and in some cases this may lead to excessive primary production in a
process known as eutrophication. Eutrophication initially increases primary productivity but
when excessive it can create cascades of effects in marine ecosystems, including increases in
phytoplankton blooms that reduce light levels reaching the sea floor, subsequent oxygen
Manaaki Taha Moana Report No. 1
25
depletions as blooms die and increase detrital levels on the seafloor, large scale losses of
benthic prey assemblages that support finfish fisheries, loss of seagrass and macrophytes,
toxicity effects, changes in species composition and reductions in harvestable fish and shellfish
(Morrison et al., 2009). Estuaries tend to be naturally nutrient-rich because land-derived
nutrients are concentrated where run-off enters a confined channel, and are vulnerable to
eutrophication especially when tidal flushing is limited by constrained openings to the sea.
BOPRC has a Natural Environmental Regional Monitoring Network (NERMN), which
includes the monitoring of 16 streams and rivers flowing into Tauranga Harbour and 18
estuarine sites (13 current in 2005). Levels of nutrients (nitrogen and phosphorous) within the
harbour generally declined over the monitoring period 1991-2005. However, these decreases
were not always statistically significant and some individual monitoring sites displayed an
increasing trend (Scholes, 2005). A majority of stream sites monitored in the Tauranga area
still have elevated nutrient levels that support undesirable biological growths (Scholes et al.,
2011).
Nutrient levels prior to development are not known, and threshold levels for the current
ecological health of the harbour are also unknown. Nutrient levels and nutrient inputs to the
harbour have been raised considerably by human induced changes in land use including runoff from fertilizers and past inputs from sewage disposal. Most point source discharges of
nitrogen and phosphorus into the harbour, however, were removed in the early to mid 1990s
(S. Park, pers. comm.). Dissolved inorganic nitrogen levels within the estuary are greater than
Australian and New Zealand Environment and Conservation Council (ANZECC, 2000a)
recommended trigger levels for estuaries (15 mg m-3) (Scholes, 2005). These guidelines are
based on southeast Australian ecosystems, however, and are not appropriate for Bay of Plenty
waters in which oceanic water with much higher nitrogen concentrations (compared to
southeastern Australia) mixes with fluvial water (ANZECC, 2000a). More relevant are trends
in nutrient concentrations over time.
A report by BOPRC (Scholes and McIntosh, 2009) describes water quality trends at 12 river
sites during the period 1989-2008, which helps to identify the sources of nutrients entering the
harbour. No overall trend was found in nutrient (nitrogen and phosphorous) concentrations,
with some rivers displaying increasing trends while others showed a decrease. Decreasing
trends were linked with improved rural practices, better control of surface runoff and land use
changes while increasing trends were associated with agriculture and increasing runoff from
recently harvested forest. Rocky Stream had elevated nitrogen concentrations (2.3 g m-3)
compared to other sites due to a high plant biomass on this slow moving stream. The
Omanawa, Kopurererua and Waimapu streams also had higher than average total nitrogen (1.1,
1.0 and 0.8 g m-3 respectively). Much of the nitrogen in the latter two streams was in the form
of total oxidised nitrogen, which may indicate that livestock agriculture was the major source
(Scholes and McIntosh, 2009). Phosphorus levels, like nitrogen, were highest in the Rocky
and Kopurererua Streams (0.04 and 0.05 g m-3). Streams with higher total phosphorus levels
tended to have a larger proportion of phosphorus in the particulate form, which can be linked
to suspended solids loading in these streams.
26
Manaaki Taha Moana Report No. 1
3.4. Pollutants
There is low to moderate contamination by heavy metals in sediment surrounding
industrial stormwater drains in the harbour (2009).
Te Maire Rd industrial area is an area of high heavy metal contamination (2009).
Zinc levels exceeded at least the low ANZECC guideline value for all sites bar one
(2009).
PAHs in sediments surrounding stormwater drains exceeded the lower ANZECC
guideline value (2009).
Copper and zinc levels were higher in shellfish from the Plumbers Point/Te Puna
site than other locations in the harbour (2010).
Heavy metals surrounding Omanu and Katikati ocean outfalls are generally within
consent limits (2008).
Levels of organochlorines in Tauranga Harbour are comparable to the Manukau
Harbour and Hauraki Gulf (1994).
A number of studies have examined pollutants within Tauranga Harbour, including plastic
particles (Gregory, 1978), heavy metals (McIntosh, 1994; McIntosh and Deely, 2001; Park,
2003; Park, 2009), pesticides (Burggraaf et al., 1994; Park, 2003; Scobie et al., 1999), PCBs
(polychlorinated biphenyls) (Burggraaf et al., 1994; Park, 2003; Park, 2009; Scobie et al.,
1999), PAHs (polycyclic aromatic hydrocarbons) (Park, 2003; Park, 2009) and resin acids
(Healy et al., 1997; Tian et al., 1998). The ANZECC 2000 interim sediment quality guidelines
provide both a level at which a contaminant may have sub-lethal effects on species and a
higher level that indicates potential acute toxicity (ANZECC, 2000b). Despite the guideline
values, it is difficult to determine safe levels as much is still unknown about the effects of
these pollutants, particularly on sensitive species. Most of the substances listed above were
deemed to be within ANZECC guidelines (where these exist), with the exceptions being heavy
metals and PAHs at some locations.
Figure 9 shows sites that have been sampled for metals and PAH contaminants in recent years.
A 2006 to 2008 survey of metal concentrations in sediments from seven coastal and estuarine
sites around Tauranga Harbour found no results that exceeded ANZECC interim sediment
quality guidelines (based on < 500 m particle size) (Park, 2009). The concentration of
contaminants (PAHs and metals) in sediments collected from 31 Tauranga Harbour sites in
2006 also showed no results that exceeded sediment quality guidelines (based on whole
sediment analysis) (Park, 2009). When standardized to the mud fraction (< 63 m particle
size), however, some metal concentrations (arsenic, lead and zinc) from a site in the Waikareao
Estuary were above guidelines. ANZECC interim sediment quality guidelines recommend
standardising to the mud fraction to address the tendency for pollutants to accumulate in fine
silts and clays rather than sands and coarse rock material (ANZECC, 2000b).
Manaaki Taha Moana Report No. 1
27
±
North Island
!
!
Expanded area
!
! !
!
!
Tauranga Harbour
Bay of Plenty
!
!
!
!
!
!
!
!
Te Maire Rd
industrial area
!
!
0
2.5
!
Figure 9.
5
10 km
!
!!
!
!
!
!
Waikareao site
with metals above
ANZECC guidelines
! !
!
!
!
2006 contaminants survey (3 yearly)
!
2006-2008 coastal and estuarine ecology surveys (annual)
!
2008 stormwater survey
!
!
!
!
!!
!
!!
!
!
!
!
!
!
!!
Monitoring sites for metals and PAH contaminants in and near Tauranga Harbour 2006-2008.
Inset shows location of Tauranga Harbour within the North Island of New Zealand. Source: (Park,
2009).
Stormwater outlets that drain from industrial areas have been identified as the key source of
pollutants to Tauranga Harbour (Burggraaf et al., 1994; Park, 2009). The Bay of Plenty
Marine Sediment Contaminants Survey (Park, 2009) found low to moderate contamination by
heavy metals in sediment samples from around industrial area stormwater drains in Tauranga
Harbour. When standardised to the mud fraction, however, there were some reported high
levels of contamination (Table 5). Te Maire Rd industrial area was an area of high
contamination, exceeding at least the lower guideline value for every metal except mercury
(Table 5). Zinc levels exceeded at least the low guideline value for all sites bar one (Table 5).
28
Manaaki Taha Moana Report No. 1
Park (2009) noted similar contamination patterns have been found for Auckland drains from
industrial sites and concluded that industrial areas contribute high levels of contaminants. Ongoing monitoring of contaminants and strategies to reduce the contaminants have been
implemented (S. Park, pers. comm.).
Table 5.
Concentrations of PAHs and heavy metals (mg kg-1 dry wt) at stormwater impacted sites in and
around Tauranga Harbour standardised to the 63 m (mud) sediment fraction. ANZECC Interim
Sediment Quality Guideline values (ISQG) for “low” (orange font; possibility of sublethal effects)
and “high” (red font; possible toxicity) are provided at the bottom of the table.
Freshwater Sites
Waimapu River
Maleme St drain
Kopurererua Tamatea Dr
Kopurererua Waihi Rd
Te Maire Rd below Manu
Te Maire Rd above Manu
Marine Sites
Grace Rd 0-10 m
Grace Rd 50 m
Maxwell Rd 0-10 m
Maxwell Rd 50 m
Harbour Dr 0-10 m
Harbour Dr 50 m
Fraser Rd 0-10 m
Faser Rd 50 m
Welcome Bay 0-10m
Welcome Bay 50 m
ISQG Low >
ISQG High >
Source: (Park, 2009)
PAH
0.3
0.3
0.0
0.2
4.6
4.1
3.8
0.3
17.1
4.1
4.7
0.6
2.9
3.1
8.2
0.3
4
45
As
24
14
15
13
54
81
Cd
1.0
0.4
9.1
3.2
37
39
48
24
25
73
16
20
70
0.5
0.5
1.4
0.3
1.5
10
Cr
26
12
11
17
373
154
38
32
35
100
46
35
128
21
80
270
Cu
46
20
21
22
522
368
72
34
74
214
128
25
65
270
Pb
75
47
54
53
597
261
Hg
110
60
152
44
58
131
119
129
308
109
50
220
2.2
2.6
0.15
1
Ni
Zn
377
133
43
4851
3321
635
400
646
218
315
742
547
525
1179
148
200
410
PAHs are commonly derived from incomplete combustion of organic material or petroleum
and coal products (Park, 2009). The Bay of Plenty Marine Sediment Contaminants Survey
(Park, 2009) found that PAHs in sediments around stormwater drains exceeded the lower
ANZECC sediment quality guideline value when standardized to the mud fraction (Table 5).
Park (2009) suggested that coal tar, asphalt and engine exhaust were the sources of these
pollutants.
Shellfish monitoring (pipi, oysters and cockles) also measures metal levels (arsenic, copper
chromium, nickel, lead and zinc). Over the 2009/10 season no risk to human health was
observed according to current guidelines (Scholes, 2010) but it should be noted that the
Australia New Zealand Food Standards Code (2010) only has standards for arsenic (< 1 mg kg
-1
) and lead (< 2 mg kg -1). Copper and zinc levels were higher in shellfish from the Plumbers
Point/Te Puna site (4.3 mg kg -1 Cu; 120 mg kg -1 Zn) than other locations within the harbour
(0.62-1.6 mg kg -1 Cu; 4.2-4.9 mg kg -1 Zn) (Scholes, 2010). This is the only site that used
oysters (Tiostrea chilensis lutria) as a test species and it has been suggested that oysters may
show elevated levels of copper and zinc compared with other bivalves because they are
attached to a surface above the sediment rather than living within the sediment (Scholes,
2010).
Manaaki Taha Moana Report No. 1
29
It is difficult to determine what constitutes low and high risk contamination because the effect
of a pollutant on aquatic organisms depends on the habitat environment and the sensitivity of
the species. Many pollutants are characteristically toxic and tend to accumulate and persist in
harbours and estuaries due to restricted water circulation and the population pressures of the
surrounding catchment. Areas with multiple toxins may be exposed to greater environmental
risk due to compounding effects of pollutants. Sessile species are particularly at risk as they
cannot move to another location to avoid contamination. There can also be problems in the
food chain where higher order predators consume contaminated organisms and the toxins
accumulate in their bodies (bioaccumulation). There is potential then for human health to be
affected by eating contaminated seafood.
3.5. Bacterial contamination
Despite bacterial contamination in streams and rivers in the catchment, the
microbiological water quality standards for recreation are rarely exceeded in
Tauranga Harbour, although shellfish contamination can occur (2011).
Bacterial contamination in Tauranga has many possible sources: wastewater
treatment plants and leaky pipes, septic tanks, livestock farming, birds, marine vessels
and meat processing plants.
Tauranga City has two wastewater treatment plants (Chapel Street and Te Maunga)
and Katikati also has a wastewater treatment plant (Prospect Drive), all of which have
discharges outside of the harbour and in most cases meet Enterococci consent limits.
Three seepages were detected from Te Maunga oxidation ponds but it is unlikely they
are impacting the ecology of the area (2006).
A new pipeline is being built to transfer sewage from Tauriko/Greerton to the Te
Maunga wastewater treatment plant (2011).
Tanner’s Point, Ongare Point and Te Puna have been identified as areas with on-site
wastewater treatment systems that pose a risk to water quality (2006).
Open coastal sites had low levels of faecal contamination and received ‘Very Good’
ratings (2010).
Estuarine sites had low levels of faecal contamination in most cases and received
‘Fair’ to ‘Very Good’ ratings, except Otumoetai Beach Reserve, which was given a
‘Poor’ rating (2010).
River sites had high levels of faecal contamination and received ‘Very Poor’ to ‘Poor’
ratings, except the Tuapiro Stream, which was given a “Fair’ rating (2010).
Shellfish from most sites in the harbour (5 out of 7) met recommended safety
standards for consumption (2010).
Faecal coliform (Escherichia coli) levels in shellfish at the Tilby Point/Otumoetai and
Plumbers Point/Te Puna sites were above guideline levels. Potential sources of
contamination include rural runoff and adjacent communities with on-site wastewater
treatment systems.
Bacterial contamination in estuarine environments typically originates from faecal matter, of
which there are multiple sources in a catchment. These include wastewater treatment plants,
on-site wastewater treatment systems (e.g. septic tanks), leaky sewage infrastructure, livestock
agriculture, avian populations, marine vessels and meat processing plants (Scholes et al.,
30
Manaaki Taha Moana Report No. 1
2009). Tauranga City has two wastewater treatment plants while rural households treat faecal
matter through on-site treatment systems (e.g. septic tanks and on site ground dispersal).
Sewage spills, overflows, leaky infrastructure and stormwater cross-contamination are constant
maintenance issues (Scholes et al., 2009).
Water monitoring is carried out by councils to assess the effectiveness of the sewage treatment
systems and risk to human health. Over the warmer months (Oct-Mar) recreational waters and
shellfish are monitored for risks to human health from faecal and heavy metal contamination
(metals are discussed in the previous section).
3.5.1. Sewage systems in the Tauranga region
Wastewater Treatment Plants
Tauranga City has two wastewater treatment plants, one at Chapel Street and the other at Te
Maunga. Katikati also has a wastewater plant on Prospect Drive, with the outfall discharging
on the eastern (sea-side) of Matakana Island (Western Bay of Plenty District Council, 2009).
Wastewater was discharged into the harbour until 1996. Now treated wastewater from the Te
Maunga plant is discharged into oxidation ponds and wetlands before being pumped out to sea,
950 m off the coast of Omanu (Tauranga City Council, 2009b). Effluent from the Chapel
Street treatment plant is disinfected with ultraviolet light and the majority is then pumped to
the Te Maunga wetlands and discharged out to sea. The sludge from both sites is turned into
biosolids, which are sent to landfills or can be used as a soil conditioner under controlled
conditions (Tauranga City Council, 2009b).
The Tauranga City Council measures biochemical oxidation demand (BOD5), total suspended
solids and Enterococci levels (Table 6) in wastewater prior to discharge from the Omanu
ocean outfall and these compliance conditions were met over the 2004 to 2008 period
(Tauranga City Council, 2009b). Enterococci concentrations are also measured in water
samples from the receiving environment along with Escherichia coli, arsenic and trace metal
concentrations in shellfish from that area (Table 6). BOPRC reports that discharge has
remained well within Enterococci consent limits over the past few years and, therefore, there is
low risk of contamination reaching the beach (Scholes, 2008b). Four of the 41 shellfish
samples over the 2006/2007 period detected E. coli concentrations just within consent limits as
suitable for human consumption (Scholes, 2008b).
Water from the Katikati ocean outfall receiving environment is measured for Enterococci and
faecal coliforms (Table 6) (Scholes, 2008b). Aside from three elevated faecal coliform results
(16, 28 and 56 faecal coliforms 100 ml-1) in February 2005, consent conditions were met
throughout the 2004-2008 period (Scholes, 2008b).
Manaaki Taha Moana Report No. 1
31
Table 6.
Compliance conditions 10.1,10.2 and 11.1 of consent 62878 for the Omanu ocean outfall and
consent conditions for the Katikati ocean outfall.
Wastewater prior to discharge (twice weekly sampling, 13 week period)
Analyte
No more than 16 values
No more than 3 values
shall exceed
shall exceed
-1
BOD5 (mg L )
25
50
Total suspended solids (mg L-1)
30
80
-1
Enterococci (cfu 100 ml )
3 500
n/a
Water from the receiving environment (20 samples per year)
Analyte
No more than 13 values
No more than 1 value
shall exceed
shall exceed
Enterococci (cfu 100 ml-1)
35
40
Katikati
Water from the receiving environment
Outfall
Analyte
Consent conditions
Faecal coliforms
Median ≤ 14 n 100 ml-1
No more than 10% should exceed 43 n 100 ml-1
Enterococci
Median < 35 n 100 ml-1
All results < 101 n 100 ml-1
Source: (Morris, 2006; Scholes, 2008b)
Omanu
Outfall
In addition to monitoring of wastewater discharge and the receiving environment, the Te
Maunga oxidation ponds are also measured each year for seepage into Rangataua Bay. Three
small seepage sites were detected in the adjacent intertidal area in both 2002 and 2006 (Morris,
2006). Two of the seepage sites noted in 2006 had low faecal coliform counts but counts were
elevated at the third site. Faecal coliform counts were also high in the Mangatawa tributary,
which drains the tidal marsh between the pond and a closed landfill. Due to the small scale of
the seepages, it is unlikely that they are impacting the ecology of the area and the abundance of
titiko in the intertidal areas adjacent to the ponds supports this assumption (Morris, 2006).
The Tauranga City Councils reports that Tauranga’s wastewater network is generally in good
condition, however, some of the concrete and asbestos cement truck sewers laid in the 1970s
have corroded and require replacement or rehabilitation (Tauranga City Council, 2009b).
Additionally, approximately 20 pumping stations no longer comply with the council’s Code of
Practice for Development in terms of pumping capacity and emergency storage (Tauranga City
Council, 2009b). Between 2004-2008 there was an average of 12 pipe blockages per 100 km
of sewer (120 blockages per year), which is below the national average of 34 (Tauranga City
Council, 2009b). Over this period there was also an average of 1.5 overflows per 100 km of
sewer (15 overflows per year) but this number may exclude some overflows caused by
blockages (Tauranga City Council, 2009b). To cater for Tauranga’s growing population the
Te Maunga treatment plant is being upgraded and a new southern pipeline is being built to
transfer sewage from Tauriko/Greerton to the Te Maunga wastewater treatment plant
(Tauranga City Council, 2010). The southern pipeline will reduce pressure on the rest of the
city’s wastewater system.
32
Manaaki Taha Moana Report No. 1
On-Site Sewage Treatment Systems
Several smaller communities bordering the harbour do not have reticulated wastewater systems
and instead use on-site wastewater treatment systems. Of these, Tanners Point, Ongare Point
and Te Puna have been identified as having risks to water quality from their on-site wastewater
systems. Omokoroa was part of the zone but has now been linked to the city’s reticulation
system (Western Bay of Plenty District Council, 2009).
A 2006 survey reported that all three sites showed some evidence of contamination from septic
tank effluent but despite this they still had good recreational water quality (Scholes, 2007).
On-site inspection of septic tanks at Tanners Point found approximately half of them failed the
inspection criteria, primarily due to under size tanks, however disposal fields were generally in
good condition. Tanners Point had notable contamination around the boat ramp and foreshore,
with elevated levels of faecal contaminants, although on average these were below
recommended contact recreation guideline values. Recently, the Western Bay of Plenty
District Council has upgraded a public toilet block located a couple of hundred metres away
from the boat ramp drain outlet in the hope of reducing contamination at this site (Weiss,
2010).
Monitoring at Ongare Point (1991-1992 and 1997-2005) showed two drain sample sites with
consistently high nitrate-nitrogen (median 5 g m-3 over 1997-2005) and Enterococci
concentrations (median 740 cfu 100 ml-1 over 1997-2005) over the current marine red alert
level for bathing water quality guidelines (280 cfu 100 ml-1) . The high nitrate-nitrogen levels
indicate that some seepage from septic tank systems is occurring. Recreational water quality
(2003-2010) has been relatively good, with Enteroccoci concentrations generally below orange
alert levels (140 cfu 100 ml -1) except during extreme events (n=10). The greatest risk to users
is, therefore, contact with contaminated inflows to the harbour (Scholes, 2007).
In 2003, approximately half of the Te Puna on-site wastewater treatment systems failed to
meet maintenance programme criteria and 20% of these had a soakage field/hole failure
(Futter, 2003). Monitoring in 2006 showed four drains with high bacterial contamination
consistent with what would be expected of poorly treated or almost raw septic tank effluent
(Scholes, 2007). The main drain (Waitui) also had elevated nutrient levels, indicating
contamination is coming from two or more sources. Despite the elevated bacteria and nutrient
levels, recreational water quality (2003-2010) at Te Puna is relatively good, probably due to
dilution and the tidal impact of the harbour, however, contamination of the foreshore remains a
risk to users (Scholes, 2007).
3.5.2. Recreational bathing sites
Over the warmer months (Oct-Mar) BOPRC monitors recreational (bathing) water quality at
15 popular sites in the Tauranga Region, shown in Figure 10, to monitor and identify risks to
public health from faecal contamination (Scholes, 2010). Sampling is carried out every 1-2
weeks to determine levels of faecal coliforms, E. coli and Enterococci as indicators for faecal
Manaaki Taha Moana Report No. 1
33
contamination. A three tiered management framework, developed by the Ministry for the
Environment (MfE) and the Ministry of Health (MoH), is used to signal when recreational
waters are potentially at risk to users (MfE and MoH, 2003). Green (surveillance) indicates an
acceptable risk to recreational water users, orange (alert) indicates increased risk of illness and
red (action) indicates unacceptable risk to users (MfE and MoH, 2003) (Table 7). A Suitability
for Recreation Grade (SFRG) rating is also used, combining a qualitative assessment of a
recreational site and direct measurements of a bacteriological indicator to describe the general
risk of faecal contamination at a site (MfE and MoH, 2003).
Open coastal sites (n=3; Figure 10) in the Tauranga Region (2009/10 bathing season) had very
low levels of contamination as indicated by Enterococci bacteria (median concentration < 3
cfu 100 ml-1), within the green range in all cases (Scholes, 2010). All sites received ‘Very
Good’ SFRG ratings and no significant sources of impacts were noted.
North Island
!
±
!
!
!
Expanded area
Bay of Plenty
Tauranga
Harbour
!
!
!
!
!
!
!
!
!
!
0
Figure 10.
34
2
4
8 km
!
!
Marine bathing sites
!
Estuarine bathing sites
Bay of Plenty Regional Council monitoring sites for bathing water quality. Inset shows location of
Tauranga Harbour in the North Island of New Zealand. Source: (Scholes, 2010).
Manaaki Taha Moana Report No. 1
Table 7.
Mode
Surveillance, alert and action levels for bacterial contamination of fresh and marine waters.
Freshwater Guideline
(E. coli count in colony
forming units per 100 ml)
Single sample ≤ 260
Marine Guideline
(Enterococci count in colony
forming units per 100 ml)
Single sample ≤ 140
Green
(Survelliance)
Single sample > 260 and ≤ Single sample > 140 and ≤
Orange
550
280
(Alert)
Single sample > 550
Two consecutive single
Red
samples > 280
(Action)
Source: MfE and MoH (2003) in (Scholes, 2010)
Recommended Management
Response
Routine monitoring
Increased monitoring, identify
possible sources
Public warnings, increased
monitoring, source investigation
Estuarine sites (n=12; Figure 10) were also below the orange level for most of summer,
however, five sites reached extremes above the orange alert level (but less than the red alert
level). The median Enterococci concentration for estuarine sites was below 25 cfu 100 ml-1.
While most sites had ‘Fair’ to ‘Very Good’ SFRG ratings, the Otumoetai Beach Reserve site
had a ‘Poor’ SFRG rating, primarily due to higher Enterococci concentrations in previous
seasons. This was a decrease from its 2008 SFRG rating of ‘Fair’ (Scholes, 2008a). The
primary impacts in this area are from agricultural activities, birds and feral animals delivered
via the Wairoa River, and an overflow structure for sewage reticulation located nearby
(Scholes, 2008a).
It should be noted that three of the estuarine sites had ‘Follow Up’ SFRG ratings, meaning the
historical bacteriological levels do not correlate with the assessed risk of faecal contamination,
so cannot necessarily be considered low risk. At the Te Puna site this is due to a ‘Very High’
risk of contamination (on-site sewage disposal systems) coupled with a fairly good record in
terms of faecal contamination (95 sample percentile 41-200 Enterococci 100 ml-1). The other
two ‘Follow Up’ sites had ‘Fair’ and ‘Good’ SFRG ratings in 2008 (Scholes, 2008a).
BOPRC also monitors bacterial contamination of rivers and streams within the harbour
catchment. River sites have poor water quality with respect to faecal contamination as
indicated by E. coli bacteria (Scholes, 2010). All 19 sites within the Tauranga area failed to
meet standards for bacterial contamination(Scholes et al., 2011). The Kaiate Stream and
Waimapu River sites showed the highest E. coli levels of the 27 river sites monitored in the
Bay of Plenty Region (median concentration ~425 and 180 cfu 100 ml-1 respectively);
contamination in the Kaiate Stream has been linked with stock having access to waterways
(Scholes, 2008a). Exceedances usually occurred after rainfall events (Scholes, 2010). SFRG
ratings for Tauranga Region rivers were ‘Poor’ to ‘Very Poor’ except the Tuapiro Stream,
which was given a “Fair’ SFRG rating. The Uretara Stream had dropped from a ‘Fair’ SFRG
rating 2008 to ‘Poor’ in 2010. The Uretara Stream was mainly affected by urban stormwater
but the primary impact for the other rivers was runoff from agriculture (Scholes, 2008a).
The Environment Bay of Plenty Ten Year Plan 2009-2019 has a key performance indicator
(KPI) for the performance of the region’s recreational bathing sites against MfE and MoH
guidelines (Environment Bay of Plenty, 2009b). Of the five sites in the Bay of Plenty that did
Manaaki Taha Moana Report No. 1
35
not meet the 95% compliance target for marine and lake sites, three were from the Tauranga
Region. All river sites in the Tauranga Region met the 85% compliance target. BOPRC does
not currently meet the recommended MfE and MoH sampling frequency for all sites (20 per
season, 100 over five years).
Overall, open coastal waters around the Tauranga Harbour showed good water quality in terms
of faecal contamination and received ‘Very Good’ SFRG ratings. Estuarine sites had low
levels of faecal contamination in most cases and generally received ‘Fair’ to ‘Very Good’
SFRG ratings. River sites had high levels of faecal contamination and received ‘Very Poor’ to
‘Poor’ SFRG ratings in most cases.
3.5.3. Shellfish contamination
Over the warmer months (Oct-Mar) BOPRC monitors shellfish from open coastal and
estuarine sites around Tauranga Harbour to determine if they are safe for consumption
(Scholes, 2010). Species sampled are pipi (Paphies australis), cockle (Austrovenus
stuchburyi) and oyster (T. chilensis lutria).
Shellfish are tested for faecal coliforms, E. coli and Enterococci as indicators for faecal
contamination. MoH guidelines recommend faecal coliform levels in flesh less than 330 MPN
(most probable number) per 100g with levels of 230-330 MPN 100 g -1only marginally
acceptable (MoH, 1995). New Zealand Food Safety Authority (2006) standards are used for E.
coli and they recommend that the median MPN must not exceed 230 E. coli per 100 g and that
not more than 10% of samples must exceed an MPN of 700 per 100 g. Over the 2009/10
season shellfish from most sites (5 out of 7) around Tauranga Harbour met recommended
safety standards for consumption. E. coli levels at the Tilby Point/Otumoetai and Plumbers
Point/Te Puna sites, however, were above standards (median 240 and 300 MPN 100 g -1
respectively) and faecal coliform levels were only marginally acceptable (240 and 300 MPN
100 g -1). Around 50 mm of rain is likely to have influenced the elevated E. coli levels at
Plumbers Point/Te Puna (Scholes, 2010), however, previous studies have found that oysters
from Te Puna consistently show high levels of contamination (Scholes, 2008a). Potential
sources of contamination include rural runoff from the stream and adjacent communities with
on-site wastewater treatment systems (Scholes, 2008a).
It should be noted that Scholes et al. (2009) finds no evidence of a distinct relationship
between faecal indicator bacteria (E. coli and Enterococci) and positive viral tests (norovirus
and adenovirus) in shellfish. This suggests indicator bacteria may not be reliable indicators of
viral contamination in shellfish, thus shellfish may not be safe to eat when the bacterial quality
is within currently accepted microbiological limits, and vice versa. Sites regularly
contaminated with viruses were those closest to urban areas and, therefore, most likely to be
accessed by the shellfish gathering population (Scholes et al., 2009).
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4.
FLORA AND FAUNA OF THE HARBOUR
4.1. Marine flora
Marine flora encompasses the primary producers within the harbour including phytoplankton,
macroalgae (e.g. seaweeds), marine plants (e.g. seagrass, mangroves) and wetland vegetation.
They use sunlight, nutrients and carbon dioxide to grow and capture energy, forming food for
animals such as zooplankton, invertebrates and fish. This section discusses the current state of
marine flora in Tauranga Harbour. Sea lettuce is discussed separately from the rest of the
macroalgae because considerably more research has been carried out on this group.
4.1.1. Phytoplankton
Shellfish collection closures have regularly occurred in the harbour since 2008, as a
result of toxic phytoplankton species (2011).
Information specific to phytoplankton of the harbour is sparse (2011).
Phytoplankton biomass is dominated by diatoms and is temporally diverse (2003).
Pelagic phytoplankton is the dominant food source for filter feeders but in areas with
strong currents benthic phytoplankton might be an important food source (2003).
Phytoplankton are tiny floating algae that are usually too small to be seen individually by the
naked eye. They play an important role in ecosystems in terms of nutrient and carbon
recycling. Through the process of photosynthesis, phytoplankton consume carbon dioxide on
a scale equivalent to forests and other land plants (Word et al., 2010) and produce half of the
world’s oxygen (Ramanujan, 2005). Their growth relies on nutrients such as nitrogen and
phosphorus and algal blooms may be stimulated when these nutrients are available in excess.
Algal blooms may cause hypoxia (oxygen depletion in the water) due to the decomposition of
dead phytoplankton.
Some phytoplankton species produce toxins, which may enter the food chain through filterfeeding animals such as shellfish. The New Zealand Food Safety Authority (NZFSA) has
undertaken routine monitoring in Tauranga Harbour for toxic phytoplankton species to
regulate shellfish collection closures since 2003. There were no closures in Tauranga Harbour
until 2008, although biotoxin warnings were occasionally issued for some limited areas (T
Ngawhika, pers. comm.). From December 2008 to March 2011, apart from a period from
February to December 2009, a warning was in place advising the public not to consume
shellfish collected from much of the Bay of Plenty, including Tauranga Harbour (Toi Te Ora,
2011). The phytoplankton species primarily responsible for the closures have been
Alexandrium minutum and A. catenella, which can cause paralytic shellfish poisoning (PSP) (T
Ngawhika, pers. comm.).
Information specific to phytoplankton of Tauranga Harbour is sparse. BOPRC reported levels
of chlorophyll-a (an indicator of phytoplankton) in Bay of Plenty open waters using satellite
Manaaki Taha Moana Report No. 1
37
imaging (Park and Longdill, 2006), but that study was at a coarse scale and did not encompass
Tauranga Harbour. Safi (2003) examined microalgal assemblages within Tauranga Harbour in
the benthos and directly above the sediment where suspension feeders feed (~10 cm).
Phytoplankton biomass was dominated by diatoms and was negatively correlated with
turbidity; larger phytoplankton cells were less able to cope with sediment. Pelagic
phytoplankton appeared to be the dominant food source for filter feeders in the region as only
1% to 23% of the biomass near the sediment surface was benthic in origin. Strong links were
observed between benthic and pelagic microalgal populations with the proportion of benthic
microalgae in suspension strongly correlated with current speed and turbidity. This
relationship suggests that, in areas with strong currents, benthic microalgae may also be an
important source for filter feeding organisms.
Many aspects of phytoplankton dynamics (e.g. growth, mortality, the dominance and
succession of species) in Tauranga Harbour are unknown. As a primary producer,
phytoplankton plays a pivotal role in the food web of the harbour, so further research might be
warranted to improve understanding of the temporal and spatial dynamics of the key
taxonomic groups.
4.1.2. Macroalgae
A survey adjacent to the Port found 23 species of macroaglae with red turf-like
algae most common (2006).
Sea lettuce, Neptune’s necklace, Gracilaria secundata, pink coralline turf algae,
Gelidium caula cantheum, and Ceramium species were identified as being very
abundant in the soft shore areas of the harbour (1994).
Macroalgae refers to any type of seaweed that is visible to the eye. There are three distinct
categories: brown, green and red seaweeds. Often these species form canopies, much like a
land-based forest canopy. Other times they form ‘turf-like’ (< 5 cm tall) clumps on rocks.
Many species form crusts over rocks and other hard surfaces and are then referred to as
coralline algae. They are hard (like a coral) and are predominantly bright pink in colour.
Some macroalgae provide many benefits to an ecosystem (e.g. kelp) while others are perceived
as nuisance species (e.g. sea lettuce) and may have negative impacts.
Macroalgae generally dominate rocky reef communities in coastal New Zealand.
Taxonomically, east coast communities resemble one another, with no one location having
distinctly different species (Beaumont et al., 2008). As such, habitats can be broadly classified
by dominant algal types (e.g. kelp, turf-like, bare space) and these descriptors are often used
for broad-scale management (Shears et al., 2004). Mixed kelp stands dominate shallow
subtidal areas in New Zealand (Cole, 1993) and form important habitats, including nursery
areas for small invertebrates and finfish (Morrison et al., 2009). Mixed “turf-like”
assemblages of species are common under kelp canopies or in exposed environments where
large species cannot withstand conditions (refer Cole 1993). Land based stressors (e.g.
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sedimentation and nutrient loading) can result in the loss of larger canopy covering
macroalage, which have important links to kai moana, and replacement by prolific weedy
species (Russell and Connell, 2005). For example, Hormosira banksii (Neptune’s necklace) is
an important habitat for juvenile fish (Morrison et al., 2009) and increased sedimentation can
decrease attachment of H. banksii zygotes by over 30% (Schiel et al., 2006). Given the
increasing land-based pressures on Tauranga Harbour, the cascading effects of these stressors
on macroalgal assemblages need careful consideration.
Intensive research has been carried out on the macroalgae communities adjacent to the Port of
Tauranga, as part of a nation-wide biosecurity monitoring programme (Inglis et al., 2006).
Despite the limited extent of the survey, it provides an indication of what species might be
present elsewhere in the harbour. Twenty three species of macroalgae were found across three
taxonomic phyla (green, brown and red macroalgae) (Table 8). Typically, red turf-like (i.e. <
10 cm in height) species dominated. An earlier survey of Tauranga Harbour in 1994,
identified sea lettuce (Ulva sp.), Neptune’s necklace, Gracilaria secundata, pink coralline turf
algae (Corallina officinialis), Gelidium caula cantheum, and Ceramium species as very
abundant within soft shore areas (Park and Donald, 1994). They noted that most other algal
species identified were rarely encountered.
Table 8.
Macroalgae species identified in the 2006 Port of Tauranga survey. Some organisms were not able
to be identified to species level.
Dictyota dichotoma var. intricate
Hormosira banksii (Neptune’s necklace)
Hymenena variolosa
Cladhymenia lyallii
Catenella nipae
Gigartina atropurpurea
Stenogramme interrupta
Trematocarpus aciculare
Gracilaria truncate
Cryptonemia latissima
Plocamium angustum
Codium fragile sp. novae-zelandiae
Codium fragile tomentosoides*
Zostera sp. (seagrass)
Ceramium sp.
Griffithsia sp.
Polysiphonia sp.
Hypnea sp.
Lomentaria sp.
Rhodymenia sp.
Enteromorpha sp.
Ulva sp. (sea lettuce)
* Non-indigenous species. Source: (Inglis et al., 2006)
Manaaki Taha Moana Report No. 1
39
Sea lettuce
Sea lettuce blooms have occurred in the harbour as far back at the 1940s.
Monitoring since 1991 shows the largest blooms occurred in 1991-1993, 1998 and
2003-2007 (2007).
Sea lettuce blooms peak in spring and decline over late summer to remain low until
the next spring (2007).
The most important factor influencing blooms is nutrient availability (2000).
Sea lettuce in Tauranga Harbour appears to be nutrient limited over summer (2007).
Greater sea lettuce abundance was recorded during El Niño years (2007).
Sea lettuce is the collective name given to green algae (Chlorophyta) of the genus Ulva. It is
distinguished by its bright green colour, thin, flat morphology, prolific growth and rapid
decomposition rate (Figure 11). It is debated whether sea lettuce is native to New Zealand or
introduced, however, Heesch et al. (2007) suggest that two of the five species in Tauranga
Harbour are most likely native (U. pertusa, Ulva spp 1), two are introduced (U. compressa, U.
intestinalis) and the origins of the other are yet to be determined (Ulva spp 3). In a 1994
survey, sea lettuce was listed as the second most abundant flora in Tauranga Harbour with an
average total cover of 3.7% (Park and Donald, 1994). Sea lettuce blooms are common
worldwide and while there is no scientific record of sea lettuce blooms prior to the 1980s,
anecdotal evidence from long-term residents indicates that they have occurred in the harbour
as far back as the 1940s (Park, 2007).
Figure 11. Sea lettuce (Ulva sp.) in Tauranga Harbour (photos: Noel Peterson)
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The vigorous spread of sea lettuce in Tauranga Harbour is due to several factors. It is a
notorious hull-fouling organism (Schaffelke et al., 2006), so is spread by human-mediated
dispersal, and can tolerate a wide range of conditions (temperatures, salinities, nutrient
concentrations), so will easily settle in new environments. The growth of sea lettuce displays
similar characteristics to an invasive or ‘r-selected’ species in that it can grow and reproduce
rapidly allowing it to quickly colonise new habitat. It has the ability to reproduce asexually via
vegetative growth, which is nutrient-controlled, so it can exploit eutrophic conditions to grow
rapidly to nuisance levels.
Sea lettuce is a component of the harbour ecosystem, providing food and shelter to animals
such as molluscs and crustaceans. Top shell (Micrelenchus huttoni) and black sea slug
(Aplysia juliana) show population increases in response to sea lettuce growth (Park, 2007).
Parore (Girella tricuspidata) grazes on subtidal sea lettuce and orange clingfish (Diplocrepis
puniceus), which are usually found in open rocky habitats, have also been seen amongst the
sea lettuce in the harbour (Gregor, 1995; Park, 2007). Due to its large biomass over summer
and high growth and decomposition rates, sea lettuce is a significant source and sink for
nutrients, particulate organic matter (POM) and dissolved organic matter (DOM), helping to
recycle them through the water column and sediment (Frankenstein, 2000).
Excess sea lettuce growth can, however, have a number of adverse effects on the ecology of
the harbour. Large amounts of sea lettuce can lead to the fragmentation and degradation of
seagrass beds, either by directly smothering the seagrass or by shading it from sunlight
(Frankenstein, 2000). Sea lettuce may also smother shellfish, such as cockle (Austrovenus
stuchburyi) and wedge shell (Tellina liliana) (Park, 2007), and prevent the settlement and
recruitment of some larvae (Olafsson, 1988) by posing a physical barrier or exuding toxic
chemicals. Dense algal mats disrupt water circulation and hence food supply to filter feeders
and cause deoxygenation of the water and sediment leading to the release of sulphides from the
sediments (Park, 2007). While sea lettuce has been shown to increase habitat and food for
some juvenile fish (Wright, 1989) it prevents other species from foraging effectively (Isaksson
et al., 1994). Shifts in communities may occur where benthic macroinvertebrates (e.g.
bivalves and polychaetes) are replaced by grazers and crustaceans that utilize the algal mats for
food and shelter (Frankenstein, 2000). Disruption to marine habitats and loss of their
inhabiting species would in turn negatively affect population numbers of birds and fish that
rely on them for food.
Prolific sea lettuce growth also poses problems to users of the harbour, with most complaints
relating to visual and odour effects (Lawrie, 2006). Sea lettuce drifts accumulate along
shorelines and once stranded anaerobic decomposition produces noxious odours and gases
(primarily hydrogen sulfide) (Frankenstein, 2000). Dense mats of sea lettuce may prevent
utilization of the beach for fishing, recreation and food gathering. Sea lettuce can clog fishing
gear, block cooling water intakes of ocean vessels and weigh down mooring buoys (Park,
2007). Amongst the Tauranga community there is confusion over the causes of sea lettuce
blooms and who (if anyone) is responsible for cleaning them up (Lawrie, 2006).
Manaaki Taha Moana Report No. 1
41
BOPRC has monitored sea lettuce cover and biomass at three sites within the harbour every
two months since 1991 (Park, 2007). High sea lettuce abundance was seen from 1991 to 1993
(~ 40-100% cover) and in 1998 (~ 60-100% cover) while abundance over 2003 to 2007 was
moderate (~ 10-60% cover) but fluctuating. Abundance in other years was generally low
(usually < 20% cover). While abundance was highly variable over time, within years a strong
seasonal trend was seen, peaking in spring (20% mean cover) and then declining over the late
summer period (13% mean cover) to remain lower (10-11% mean cover) until the following
spring (Park, 2007). Sea lettuce abundance, particularly in localized areas, is highly variable
and strongly affected by tides and winds (Park, 2007). On the other hand, a commercial fisher
who has operated inside the harbour for over 30 years says sea lettuce has become much worse
over that time, with the first major bloom occurring in 1988 (D Kiddie, pers. comm.).
Several factors influence the formation of sea lettuce blooms, including weather conditions and
hydrodynamics, but the most important is nutrient availability (Frankenstein, 2000). Nitrogen
and phosphorous determine the growth of macroalgae and nitrogen in particular controls the
growth of sea lettuce (Frankenstein, 2000). At sea lettuce monitoring sites in Tauranga
Harbour, water column measurements of available nitrogen showed lowest concentrations in
summer (0.007-0.031 NOx mgL-1) and higher levels in winter (0.027-0.147 NOx mgL-1) (Park,
2007). Nitrogen levels in sea lettuce tissue show the same trend, i.e. very low during summer
(1.54% dry weight), when plants are growing fast, and higher in winter (2.56% dry weight) as
growth slows and the algae can store extra nitrogen for when growth conditions improve (Park,
2007). Park (2007) concluded that sea lettuce in Tauranga Harbour is severely nitrogen
limited (< 2% nitrogen dry weight) over summer.
Nitrogen levels within the harbour can be influenced by inorganic inputs (e.g. land-based
runoff, outfalls) and by weather conditions, in particular the El Niño/La Niña Southern
Oscillation (ENSO). In La Niña years, easterly winds dominate, while in El Niño years,
westerly winds are more frequent. The westerly winds during El Niño years push water
offshore, which is then replaced by nutrient-rich, deep oceanic water (upwelling). Park (2007)
found a significant relationship between ENSO and sea lettuce growth, with greater sea lettuce
abundance recorded during El Niño years (70-120 % higher than average) than La Niña (50100 % lower than average). Nitrogen levels in sea lettuce tissue were also higher during El
Niño years. Many other processes may also affect sea lettuce abundance, however, such as
land derived nutrients, winds, tides, temperature and light intensity. For example, a pattern of
increasing nutrient concentration in sea lettuce tissue was observed to match the degree to
which each site is influenced by nutrient derived input form the land (Park, 2007). BOPRC is
conducting further research to assess the influence of land derived versus upwelled nutrients
on sea lettuce blooms. The question is also be investigated by a student at the University of
Waikato using isotope analysis.
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4.1.3. Other marine plants
Seagrass
Seagrass beds provide a number of ecosystem functions.
Seagrass beds have declined by 34% over 1959 to 1996, with a 90% decrease in subtidal
areas (1996).
There is some evidence of seagrass increase in Tuapiro Estuary (1996).
Sub-estuaries with large catchments showed greater loss of seagrass (1999).
Sedimentation and nutrient loading were implicated as the main factors in Tauranga
Harbour’s seagrass decline (1999).
There are currently no proposed restoration plans but studies in Whangarei Harbour
show this may be a viable option in the future (2008).
Seagrasses are native flowering plants that typically grow in subtidal and intertidal areas of
estuaries and sheltered harbours. New Zealand has only one species of seagrass (Les et al.,
2002), Zostera capricorni (Figure 12), and in 1976, the seagrass beds of Tauranga Harbour
were described as more extensive than in any other New Zealand harbour (Barker and
Larcombe, 1976). In 1994 seagrass was reported to be the most common plant or algae within
Tauranga Harbour, covering an estimated 22.5 % of the intertidal area in a survey done during
the summer of 1990/91 (Park and Donald, 1994). More recently, Tauranga Harbour has been
identified as one of nine ‘hotspots’ for seagrass distribution in New Zealand (MFish, 2006)
with a total seagrass area of 2,933 ha in 1996 (Park, 1999a).
Figure 12.
Seagrass (Zostera capricorni) in Tauranga Harbour (photos: Noel Peterson).
Manaaki Taha Moana Report No. 1
43
Seagrass meadows provide a number of ecosystem functions and are promoted by the New
Zealand Ministry for the Environment as a ‘national environmental performance indicator’ for
assessing the health of New Zealand coastal and estuarine ecosystems (MfE, 2001). Seagrass
beds enhance primary production and nutrient cycling, stabilize sediment, protect the coast
from erosion and support a number of animals and plants. They provide a nursery habitat for
juvenile fish such as snapper, trevally, parore, spotties and triplefins (Morrison et al., 2007),
protecting the small fish until they are large enough to survive in other habitats and, thereby,
supporting larger fish populations on the open coast that may have cultural or economic
significance.
A study of benthic macrofauna in Matapouri Estuary (Northland) found that seagrass beds are
by far the habitat with the greatest diversity in the estuary, containing the largest number of
species (Alfaro, 2006). Research in Tauranga Harbour also showed the highest diversity of
macrofauna is found within seagrass beds (Park and Donald, 1994). Seagrasses are a key
component of the estuarine environment and significant losses are likely to have negative
impacts on ecosystem functioning.
Globally seagrass distribution and abundance have declined significantly (Green and Short,
2003; Orth et al., 2006). Historical aerial photos show seagrass beds in Tauranga Harbour
have declined from 4,437 ha (22%) in 1959 to 2,933 ha (14%) in 1996, which is a 34%
decrease in less than 40 years (Park, 1999a). Subtidal areas showed the greatest losses with a
90% decline across the whole harbour; intertidal beds declined by 27%. Seagrass beds in areas
with large catchments were affected more than those near the harbour entrance or in subestuaries with negligible land runoff (Park, 1999a; Park, 1999b). It is unknown whether
seagrass was already in decline in 1959, or whether beds have recovered or declined further
since 1996, so the full impact of seagrass decline on harbour ecology may be less or greater
than the above numbers suggest. In the late 1990s, regional council reports suggested that
seagrass decline may be slowing and that in one area (Tuapiro Estuary), seagrass beds may be
increasing (Park, 1999a; Park, 1999b). This improvement was attributed to better
environmental practices, particularly the removal of point source nutrient discharge (sewage
was discharged into the harbour until 1994), and reductions in the amount of land runoff and
associated nutrients and sediments (Park, 1999a; Park, 1999b).
Several studies suggest that human impacts are primarily responsible for seagrass decline
(Inglis, 2003; Park, 1999a; Park, 1999b; Turner and Schwarz, 2006). As seagrass is primarily
found in estuarine and near-shore coastal environments in New Zealand, it is particularly
vulnerable to catchment land use activities and coastal development (Turner and Schwarz,
2006). Direct human impacts include mechanical damage (e.g. dredging, fishing, anchor
damage), eutrophication, sedimentation, pollution, introduced species, the effects of coastal
constructions and food web alterations while indirect impacts include the negative effects of
climate change (e.g. erosion by rising sea level, increased storms) (Duarte, 2002; Turner and
Schwarz, 2006). Impacts can also be natural, such as storm damage, disease (e.g. wasting
disease caused by Labyrinthula zosterae ) and grazing by herbivores (e.g. black swans).
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Observations of black swan feeding on seagrass beds in Tauranga Harbour showed 1-7% of
plants (including rhizome) had been removed in some areas (Park and Donald, 1994).
Light is one of the primary resources limiting the growth of seagrasses (Hemminga and
Duarte, 2000) and accordingly a reduction in available light has been cited as the most
frequent and widespread cause of seagrass decline (Turner and Schwarz, 2006). The main
factors are an increase in dissolved nutrients leading to eutrophication and an associated
increase in phytoplankton, macroalgae and epiphytes and an increase in suspended sediments
resulting in turbidity and, potentially, increased sedimentation. Runoff of nutrients and
sediments into estuaries and coastal environments, as a result of human activities, is considered
to be the greatest threat to seagrass worldwide (Green and Short, 2003; Hemminga and Duarte,
2000). Sedimentation and nutrient loading were implicated as the main factors involved in
Tauranga Harbour’s seagrass decline (Park, 1999a; Park, 1999b).
There is currently no restoration plan for the recovery of seagrass in Tauranga Harbour.
Potential sites for restoration are those with a history of seagrass existence (Fredette et al.,
1985). Conditions responsible for the loss of seagrass must have improved sufficiently and a
number of key environmental parameters must be met (e.g. water depth, nutrient levels, water
clarity) (Reed et al., 2005; Reed et al., 2004). This could be achieved by minimizing
suspended sediments, nutrients and contaminants in runoff and discharges into the harbour
using catchment management plans that incorporate the use of tools such as riparian margins,
treatment wetlands and erosion protection measures (Reed et al., 2004). In Whangarei
Harbour seagrass was transplanted from donor sites within the harbour to areas nearby, where
formerly there were extensive seagrass beds. Seagrass cover at the transplant site had more
than doubled in one year after transplanting and donor sites recovered fully within nine months
(Matheson et al., 2008). Research shows that local donor sites are best for transplanting due to
genetic similarity and exposure to corresponding environmental conditions (Jones et al., 2008).
Tuapiro Estuary may be a potential donor site for any future restoration plans in Tauranga
Harbour.
Wetland vegetation
Wetland areas within Tauranga Harbour have been surveyed and the total areas of both
terrestrial and estuarine wetlands have been quantified (Beadel et al., 2008). Wetlands occur
in both zones, with most in low lying coastal areas. The most extensive areas of wetland
remaining in the ecological district are on the northern end of Matakana Island. Dunelands
occur along the entire length of the Tauranga Ecological District coastline.
Dunelands, wetlands, saltmarsh and mangroves were found to characterize natural areas
remaining in the coastal zone. Wetlands that remain free of exotic plants were rare. Of 773 ha
of wetland in the coastal zone, 586 ha are invaded by exotic species to some degree, and 186
ha are dominated exclusively by willows. Wetlands in the semi-coastal zone exhibit a more
severe degree of invasion by exotic species (Beadel et al., 2008). Further information
including site maps and descriptions for specific areas of the Tauranga Ecological District can
be found in Beadel et al. (2008).
Manaaki Taha Moana Report No. 1
45
Mangroves
While mangroves perform many important ecological functions, there may be significant
differences between the single species mangrove habitat of New Zealand and the
complex mangrove forests of tropical regions (2010).
Mangroves are declining globally but expanding in New Zealand (2007).
Mangroves in Tauranga Harbour increased by 160% between 1943 and 2003, causing
adverse effects on amenity values and possibly harbour ecology (2003).
Mangrove expansion is likely driven by sedimentation (2010).
92 ha of mangroves have been removed from the harbour (2010).
Mangrove management initiatives are becoming more catchment focused to target the
source of the problem (2010).
Mangrove is the common name for a number of inshore tropical shrubs or trees that are
adapted to grow in salt water (Nybakken and Bertness, 2005). New Zealand is the southern
extent of mangroves’ natural range and is home to only one species, Avicennia marina (Figure
13) (Crisp et al., 1990). Mangroves require sheltered conditions for establishment so typically
occur in low-wave-energy environments with high sedimentation (Nybakken and Bertness,
2005). Overseas research shows mangroves serve a number of important ecological roles
including nitrogen cycling, trapping sediment, providing nursery areas, enhancing species
diversity, increasing ecological productivity and providing habitat and food for other species
(Food and Agriculture Organisation of the United Nations, 2007; Miththapala, 2008;
Nybakken and Bertness, 2005). In addition, by virtue of their ability to buffer shorelines from
erosion, mangroves may protect the coast from the effects of future sea level rise (Jones,
2008).
Figure 13.
46
Mangrove (Avicennia marina) spread and removal in Tauranga Harbour (photos: Noel Peterson)
Manaaki Taha Moana Report No. 1
There may be significant differences between the single species mangrove habitat of New
Zealand and the complex mangrove forests (up to 30 species) of tropical regions (Morrisey et
al., 2010). Overseas, a range of marine species have formed obligatory relationships with
mangroves but in New Zealand there are no such examples. Mangroves in New Zealand
perform a number of the same services as mangroves overseas (e.g. nutrient cycling, shoreline
protection, providing habitat diversity) but the extent to which they do so may, or may not, be
comparable. For example, while tropical mangroves provide critical nursery habitat for a
range of marine fish, Morrisey et al. (2007) argued that it is unlikely that New Zealand
mangroves are important as spawning grounds for coastal fish or as habitat for their larvae.
New Zealand mangroves show low diversity in fish species, compared with other estuarine
habitats, and could be considered as nursery or “effective juvenile” habitat for only three
species of fish (short-finned eels, parore and grey mullet) (Morrisey et al., 2007). Care should
be taken when drawing comparisons with tropical, sub-tropical and other temperate mangrove
systems and further research is needed to identify the role of mangroves in a New Zealand
context.
Globally mangroves are declining (Food and Agriculture Organisation of the United Nations,
2007), however, in New Zealand they are spreading at a rate that has led some communities to
consider them to be a nuisance. Concerns from coastal residents of the upper North Island
include reduced access, smelly mud, loss of water views, poorer fishing and shellfish gathering
and decreased property values (Green et al., 2003). Mangrove expansion has the potential to
reduce the area of intertidal flat in an estuary with associated changes in benthic invertebrate
composition (Ellis et al., 2004). Alterations in benthic communities that are prey species for
larger fauna have ecological consequences for higher trophic levels. Colonisation of intertidal
flats by mangroves also has the potential to decrease feeding and roosting areas for wading
birds (Auckland Regional Council, n.d).
Aerial mapping shows mangroves in Tauranga Harbour have increased in extent by 160% over
the past 60 years, from 240 ha in 1943 to 623 ha in 2003 (Figure 14) (S. Park, pers. comm.;
Park 2004). Much of the mangrove habitat has established within the last 25 to 40 years.
Comparison of mangrove cover between sub-estuaries from 1943 to 2003 (
Table 9) shows the greatest mangrove expansion was at Tanners Point (26 ha change in canopy
cover over 60 years) while Bluegum Bay and Waimapu had the smallest increases in
mangrove cover (2.6 ha and 4.2 ha, respectively, over 44 years) (Park, 2004).
Manaaki Taha Moana Report No. 1
47
700
Mangrove canopy cover (ha)
600
500
400
300
200
y = 2E-11e0.0156x
R² = 0.9909
100
0
1940
1950
1960
1970
1980
1990
2000
2010
Year
Figure 14.
Mangrove cover (ha) in Tauranga Harbour 1943-2003. Data provided by S Park (pers. comm.).
Table 9.
Mangrove canopy cover (ha) of sub-estuaries within Tauranga Harbour from 1943 to 2003.
Sub-estuary
Canopy cover of mangroves (ha)
Area
Change*
(ha)
1943 1959 1964 1969 1975 1982 1986 1993 1996 1999 2003
Welcome Bay
150
0.4
0.6
1.0
2.5
3.1
12.3 13.2 13.6
13.2
Tuapiro
190
0.6
1.4
2.3
13.8 17.2
17.0
Te Puna
160 13.2 15.5
24.1
33.2 29.0
15.8
Waikaraka
70
0.3
0.6
3.4
11.8 10.0
9.7
Tanners Point
n/a
0.2
0.9
19.3 26.1
29.4 26.2
26.0
Hunters Creek 460
0.2
0.4
7.2
7.7
10.6
10.4
Bluegum Bay
250
0.2
1.9
2.5
2.8
2.6
Waimapu
250
0.2
3.1
4.4
4.2
*Note: Change in cover is determined by subtracting the earliest estimate of canopy cover of mangrove for each subestuary from its respective 2003 estimate. Source: (Park, 2004).
Two main mechanisms likely account for the spread of mangroves, both directly driven by
increased sedimentation. More sediment settling in the harbour raises the level of the intertidal
seabed, allowing mangroves to colonise areas that were once too frequently inundated by the
tide (Jones, 2008). An increase in sedimentation by 2 mm per year on a wide shore profile
could allow mangroves to colonise an additional 1 m per year (Park, 2004). Once established,
mangroves reduce water movement and wind, further enhancing fine sediment deposition and
creating a positive feedback as the extent of suitable habitat for mangrove colonization
concurrently increases (Hume et al., 2010). As an example, sediment accumulation in the
Firth of Thames has increased from 20 mm per year to as much as 100 mm per year following
mangrove colonization (Auckland Regional Council, n.d).
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Fine sediments preferentially accumulate among mangrove root structures, changing the
sediment composition from sandy to muddy substrate (Stokes, 2010). Muddy substrates tend
to have higher nutrient levels, facilitating the growth of mangroves (Park, 2004). Within
Tauranga Harbour, Park (2004) found a strong correlation between average mud content of a
sub-estuary and its mangrove cover with more mangroves in muddy sediment (Table 10 and
Figure 15).
This trend is not present for all sub-estuaries, for example Mangawhai and Rereatukahia are
reasonably muddy (21% and 37% mud content) but have low canopy cover (2%). Thus, other
factors are also likely to be important in determining rates of colonisation and overall
abundance. Such factors may include global warming (e.g. increases in temperature and
carbon dioxide enhancing production), changes in hydrodynamics (e.g. reduced tidal flushing)
and increased nutrient inputs (Auckland Regional Council, n.d; Morrisey et al., 2007; Nicholls
et al., 2004; Park, 2004).
Table 10.
Canopy cover (% of sub-estuary) and mud content (% of sediment) in sub-estuaries within
Tauranga Harbour in 2003.
Sub-estuary
Apata
Wainui
Rereatukahia
Te Puna
Katikati
Welcome Bay
Mangawhai
Waimapu
Waikaraka
Tuapiro
Hunters Creek
Wairoa
Waipu
Bluegum Bay
Source: (Park, 2004)
Manaaki Taha Moana Report No. 1
Area (ha)
110
380
380
160
250
150
140
250
70
190
460
540
180
250
Canopy Cover (%)
38
22
2
18
15
9
2
2
14
9
2
2
1
1
Mud Content (%)
70
55
37
30
30
22
21
21
18
12
9
7
7
5
49
80
70
Canopy cover (%)
60
50
40
30
20
10
y = 0.0212x2 + 0.7726x + 12.682
R² = 0.7377
0
0
10
20
30
40
Mud content (%)
Figure 15.
Relationship between mud content and mangrove canopy cover in Tauranga Harbour sub-estuaries
Source: (Park, 2004).
The RMA 1991 requires a coastal permit from BOPRC for the removal of mangroves. In
2003, the Tauranga City Council was granted consent to hand remove mangroves in four
estuaries (R Donald, pers. comm.). The Estuary Care Programme was set up in 2006 to
support communities that wanted to become actively involved in harbour protection work,
including mangrove removal, and these groups became responsible for consent application
(Bay of Plenty Regional Council, 2010). There are currently 10 Estuary Care Groups and in
August 2009, they were granted consent for the mechanical removal of 92 ha of mangroves
from 11 sites (Bay of Plenty Regional Council, 2010). Removal began in January 2010 and
was completed in early 2011. At this stage, BOPRC has no further plans for mangrove
removal, however, once criteria have been developed for the assessment of potential removal,
additional areas may be identified for removal (R Donald, pers. comm.).
Environmental monitoring is required as part of the mangrove removal consent conditions and
includes an assessment of mulch accumulation and transportation, general observations and
impacts of machinery, bird monitoring and sediment transportation (Bay of Plenty Regional
Council, 2010). In June 2010, BOPRC reported that the mulch remains in situ and becomes
incorporated into the mud and the impact of machinery is minor in terms of effects to benthic
life. Wading birds, including the banded rail (Rallus philippensis) are still present in areas
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Manaaki Taha Moana Report No. 1
subject to mangrove removal (Bay of Plenty Regional Council, 2010). Sediment monitoring
transects are in place and will be monitored annually by the relevant Estuary Care Group but at
this stage there is deemed to be little visible sediment movement (Bay of Plenty Regional
Council, 2010). Dissolved oxygen levels at two mulch sites, Waikareao and Omokoroa, were
assessed six and two months, respectively, after mangrove removal (Park, 2011). A slight
reduction of oxygen levels was recorded over the mulched areas but this was not below that
recommended by the ANZECC aquatic life guidelines (80% saturation) and was similar to
those recorded in intact mangrove areas (Park, 2011). Higher levels of dissolved oxygen
depletion are likely to occur immediately after mangrove mulching and it was recommended
that this be monitored further (Park, 2011). A report on monitoring of consent conditions for
the mangrove removal is expected mid 2011 (R Donald, pers. comm.).
Mangrove removal at three of the 11 sub-estuaries where removals have occurred has also
been assessed by Lundquist et al. (2010). Local scale impacts were compared between
mangrove clearings, neighbouring unvegetated sediments and mangrove forest. Results
suggested that mulch and anoxia persisted longer than predicted even at wave exposed sites.
Mulch was predicted to disperse within a one month period but was present eight months after
mangrove removal. Impacts on benthic communities included 100% mortality of both infaunal
and epifaunal communities following mangrove removal. Sediments became anoxic with high
abundances of sulphide-reducing bacteria, and abundant nuisance algae (sea lettuce) were
recorded at mulch sites. Oxygen-depleted waters were recorded over mulch sites as compared
to control sites. Water column dissolved oxygen (DO) levels at mulch sites were as low as
30% to 60% (Lundquist et al., 2010), below the ANZECC aquatic life guidelines of 80% DO
saturation, leading to possible impacts on fish and other marine organisms.
While mangrove removal may temporarily restore some areas to previous conditions, the
spread of mangroves is a response to sediment loading from catchment runoff and until this is
addressed estuarine systems will continue to degrade. Removal of mangroves may allow some
of the accumulated mud to disperse freely but mud will continue to settle in sheltered areas
unless the sediment load decreases. Indeed, removing mangroves may facilitate the spread of
once consolidated mud into other areas of the estuary. Mangrove management initiatives
should include issues such as catchment management to address eutrophication and
sedimentation generated by anthropogenic activities (Mom, 2003). BOPRC has started work
on catchment management plans, which help land owners to develop better land use practises
to reduce sediment runoff. The New Zealand Landcare Trust is also working on sustainable
land management initiatives including riparian fencing and planting practices as part of a
Kaimai/Mamaku project (Kate Akers, pers. comm.).
4.2. Marine fauna
Marine fauna encompasses the animals within the harbour including macroinvertebrates (e.g.
shellfish), fish, large mammals (dolphins, whales and seals) and birds.
Manaaki Taha Moana Report No. 1
51
4.2.1. Macroinvertebrates, including shellfish
Soft shore macrobenthic communities in Tauranga Harbour are similar to those in
comparable habitats elsewhere in the northern New Zealand (1994).
Macroinvertebrate species richness, an indicator of ecosystem health, remained stable
over the 1990-2000 period (2000).
Polychaetes were the dominant taxonomic group in subtidal areas (1994).
Bivalves were the dominant taxonomic group in intertidal areas (1994).
Near the Bowentown entrance to the harbour there was evidence of extensive former
mussel beds (1994).
Subtidal species diversity was limited by sediment mobility with less species in areas
with low silt deposition (and therefore high currents) (1994).
Intertidal species diversity decreased with increasing with silt content (1994).
Macroinvertebrate diversity was higher in seagrass beds than on bare sand (1994).
Some species showed correlations in density due to one species providing substrate for
another (1994).
Studies of the rocky communities at the harbour entrance have indicated these areas are
very diverse with high densities of filter feeding species (1982-1991).
Cockles, wedge shells and pipi all showed a trend of larger shellfish near the harbour
entrance with progressively smaller sizes in the upper harbour (1994).
Cockles showed no change in length frequencies between 1974 and 1994 (1994).
Shellfish surveys at Otumoetai have recorded, between 2006 and 2010, a significant
increase (roughly 200%) in cockle populations and a significant decline (about 50%) in
pipi numbers (2010).
The term macroinvertebrate refers to animals that do not possess a backbone and are visible
without the use of a microscope (generally > 0.5 mm). The group includes animals such as
sponges, anemones, worms, shellfish, crabs, starfish and sea urchins but does not include fish
or mammals.
Tauranga Harbour has extensive intertidal areas (subject to submergence and exposure by the
tides) and shallow subtidal areas (always covered by water) supporting a diverse array of
macroinvertebrates. Bioresearchers Ltd. (1976a; Bioresearchers Ltd, 1976b) reported that the
harbour has exceptionally high ecological value and described it as productive, stable, rich in
species and habitat, in excellent ecological condition and of importance to the ecology of the
greater region. Park and Donald (1994) described large productive beds of shellfish
throughout the harbour, and reported that historical impacts to the ecology of the harbour
appeared to be minimal. However, pressure is now increasing due to activities such as land
use changes, increasing urbanisation and greater demands for port activities.
BOPRC monitors benthic macrofauna at 17 sites within and around Tauranga Harbour to
assess benthic community health and detect trends over time with respect to the integrity of
ecosystems. The last published report (Park, 2000a) found that species richness, an important
indicator of ecosystem health, has remained stable over the 1990-2000 monitoring period.
More recent work is needed to determine whether this trend still holds true; an updated benthic
monitoring report is expected to be completed in 2011 (R. Donald, pers. comm.).
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Other information relating to benthic macrofauna within the harbour is limited; existing studies
are either solely qualitative or limited to small geographic areas (Bioresearchers Ltd, 1974b;
Bioresearchers Ltd, 1975; Bioresearchers Ltd, 1976a; Bioresearchers Ltd, 1976b; Healy et al.,
1991; Healy et al., 1988; Roper, 1990). The Port of Tauranga has carried out a number of
localised studies through assessments of dredging and spoil dumping and via on-going support
of graduate student research projects (Blom et al., 1993; Butler, 1999; Cole et al., 1994; Cole
et al., 1995; Crozier, 2001; Foster, 1992; Gouk, 2001; Grace, 1997; Grace, 1998; Grace and
Blom, 1992; Graeme and Graeme, 1991; Graeme, 1995; Healy et al., 1998; Hull, 1996; Keeley
and Pilditch, 1998; Putt, 1996; Ross and Pilditch, 2006; Ross and Pilditch, 2009; Teaioro,
1999). Park and Donald carried out a comprehensive survey of the intertidal and subtidal soft
shore benthic communities of Tauranga Harbour, reported in 1994. While this information is
somewhat out-dated, it provides a useful baseline for future reference and gives an indication
of what species one might expect to find. Overall they found the communities to be similar to
those of comparable habitats elsewhere in northern New Zealand. The following sections on
the subtidal and intertidal areas discuss Park and Donald’s findings in more detail.
Subtidal Soft Shore
Six replicate core samples from 16 subtidal sites within Tauranga Harbour were sampled and
sieved through 1 mm mesh (Park and Donald, 1994). The dominant taxonomic group was the
polychaetes (62% of total), followed by the bivalves (19% of total) (Table 11). The most
common bivalve was the pipi (Paphies australis) (10.2% of total), which was common in
shallow subtidal areas. The nut shell (Nucula hartvigiana) and cockle (Austrovenus
stutchburyi) were also often seen (2.2% and 1.1% of total, respectively) but this was due to the
shallow nature of many of the sites, as these species prefer the low intertidal. Bivalves and
gastropods were less common in subtidal areas than intertidal but echinoderms (mainly
starfish) and crustaceans (mainly amphipods) were more frequent. Overall, the species
composition appears typical of a reasonably healthy benthic community.
Benthic communities near the entrances to the harbour are similar to Tawera-CorbulaGlycymeris bivalve communities in coarse gravels elsewhere in New Zealand. Near the
northern entrance to the harbour (Bowentown) there was evidence of extensive former mussel
beds (Perna canaliculus) but only small isolated patches of mussels remained. The loss of
these mussel beds has been attributed to overharvesting (Bioresearchers Ltd, 1976a). The
associated community included sea cucumber (Stichopus mollis), blue false crab (Petrolisthes
elongatus) and several species of fish (e.g. spotties, scorpionfish). Healy et al. (1988) reported
that marine life near the southern entrance to the harbour (Tauranga) is expected to be rich and
diverse in the coarse sediments, but sparse on the dynamic high-energy ebb-tidal delta. They
described a diverse deep channel community characterized by bivalves (Theora lubrica,
Leptomya retiaria), polychaetes (e.g. Pectinaria australis), crabs (Macrophthalmus hirtipes,
Halicarcinus varius, hermits), heart urchins (Echinocardium australe), brittle stars and horse
mussels (Atrina zelandica).
Manaaki Taha Moana Report No. 1
53
Table 11.
The numerically dominant macrofauna species recorded in 1994 subtidal surveys of Tauranga
Harbour using 1 mm mesh sieves. Also reported is the percentage composition of the total number
of individuals from the 96 (13 cm diameter) core samples collected.
Scientific name
Polychaetes
Aonides oxycephala
Heteromastus filiformis
Owenia fusiformis
Aglaophamus macroura
Oriopsis sp.
Aquilaspio aucklandica
Magelona dakini
Lumbrinereis sphaerocephala
Macroclymenella stewartensis
Sabellidae sp.
Chaetozone platycera
Perinereis sp.
Thelepus plagistoma
Bivalves
Paphies australis
Felaniella zelandica
Nucula hartvigiana
Gari stangeri
Austrovenus stutchburyi
Crustacea
Elminius modestus
Paramoera chevreuxi
Amphipod sp. m
Other
Trochodota dendyi
Urechis sp.
Patiriella regularis
Other species (64)
Source: (Park and Donald, 1994)
Common name
bristle worm
ragworm
pipi
nut shell
purple sunset shell
cockle
% composition of total
14.0
8.3
8.3
4.6
3.2
3.0
2.3
2.0
1.7
1.7
1.7
1.5
1.4
10.2
2.4
2.2
1.3
1.1
acorn barnacle
amphipod
1.8
1.6
1.6
burrowing sea cucumber
annelid worm
cushion star
1.3
1.3
1.1
20.4
As the sampling moved to shallower harbour waters and medium grained sand, turritellid
communities dominated by turret shell (Maoricolpus roseus) were observed, similar to
communities seen elsewhere in northern New Zealand (Morton and Miller, 1973). Further up
the harbour there were extensive communities associated with scallop (Pecten novaezelandiae)
and horse mussel. No detail was given for organisms associated with the horse mussel beds
but the scallops supported red algae (Delesseria and Rhodymenia leptohylla), which in turn
had associated communities of amphipods and small rissoid snails. The upper reaches of the
subtidal area had low densities of juvenile scallops and species common in the lower intertidal
zone.
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Areas of the channel with higher silt content had moderate densities of heart urchin. Shallower
subtidal areas, especially those free of silt and gravel, were dominated by olive shell (Amalda
australis), cushion star (Patiriella regularis) and cake urchin (Fellaster zelandiae). Species
observed in a 1982 subtidal soft sediment survey in Pilot Bay were similar to the domiant
species found throughout the harbour (e.g. Aglaophamus macroura, A. australis, P. regularis)
(Harrison and Grierson and Partners, 1982).
Mean species diversity (number of taxa in each sample) was 6.9. The site showing the highest
species diversity (13.3) contained a large number of horse mussels, which provided additional
habitat complexity and sediment stability. Species diversity in subtidal areas was limited by
sediment mobility, showing a negative correlation with depth and a weak positive correlation
with percentage silt content of superficial sediments. This counterintuitive trend (i.e. one
might intuitively expect species diversity to be higher in areas with low silt content) most
likely arises due the strong scouring action of currents in the channel. Deeper areas tend to
have higher current velocities and this instability makes it difficult for species to survive.
Areas with weaker currents are more conducive to colonization, and also facilitate silt
deposition. The trend is not linear and if currents were to slow sufficiently to allow the
deposition of higher amounts of silt, species diversity would be expected to decrease, as seen
in the intertidal zone.
Healy et al. (1988) described a deep community in the Port area with high species diversity,
characterized by species typical of fine or muddy offshore sediments (e.g. pink sea star, heart
urchin). The presence of such species suggests currents in the deepened Port basin are not as
strong as those sampled by Park and Donald (1994) and allow some stability. The Port area
may be somewhat unique in this respect. The sand banks in the vicinity of the Port are
characterized by clean sands with frequent beds of shellfish and quantities of loose shell
derived from the local marine fauna (Healy et al., 1988).
Healy et al. (1988) reported reduced diversity in and near the offshore dredge spoil dump
zones (outside harbour). Species diversity was reduced to approximately one third of that seen
in control areas and remaining organisms were those which can cope with unstable seabed
conditions such as bivalves (Tawera spissa), polychaetes (Sigalion sp., Lumbriconereis
sphaerocephala, A. macroura), gastropods (Antisolariumm egenum, A. australis), hermit crabs
and amphipods. It was suggested that physical smothering from the spoil dump was
responsible for the reduction in diversity.
Intertidal Soft Shore
Four replicate core samples from each of 160 intertidal sites within Tauranga Harbour were
sampled and sieved through 2 mm mesh (Park and Donald, 1994). The dominant taxonomic
group was the bivalves (46% of total), followed by the polychaetes (19% of total) and
gastropods (18% of total) (Table 12). The most abundant species were wedge shells and
cockles, each comprising about 15% of the total number of individual animals collected. The
cockle is commonly noted as a dominant intertidal species in New Zealand estuaries (Knox
Manaaki Taha Moana Report No. 1
55
and Kilner, 1973). Bivalves, gastropods and coelenterates (anemones and sea cucumbers)
were more common in the intertidal zone than the subtidal.
Table 12.
The numerically dominant macrofauna species recorded in 1994 intertidal surveys of Tauranga
Harbour using 2 mm mesh sieves. Also reported is the percentage composition of the total number
of individuals from the 640 (13 cm diameter) core samples collected and the mean and maximum
abundances (per m2) of each species.
Scientific name
Polychaetes
Scoloplos sp.
Sclecolepides benhami
Heteromastus filiformis
Aonides oxycephala
Aquilaspio aucklandica
Macroclymenella stewartensis
Perinereis nuntia var. vallata
Bivalves
Tellina liliana
Austrovenus stutchburyi
Nucula hartvigiana
Paphies australis
Felaniella zelandica
Crustaceans
Callianassa filholi
Macrophthalmus hirtipes
Halicarcinus whitei
Hemigrapsus crenulatus
Gastropods
Zeacumantus lutulentus
Zeacumantus subcarinatus
Cominella gladiformis
Diloma subrostrata
Micrelenchus huttoni
Other
Anthopleura aureoradiata
Other species (65)
Source: (Park and Donald, 1994)
Common name
% composition
of total
Mean
abundance
Maximum
abundance
6.7
2.4
1.9
1.0
1.4
1.0
2.3
30
24
13
12
30
527
678
829
377
678
15.1
14.9
11.6
2.2
1.9
194
191
149
28
24
904
2,185
3,918
2,486
1,507
ghost shrimp
hairy mud crab
pill box crab
hairy handed crab
<1
<1
<1
<1
5
13
10
4
527
301
301
226
horn shell
6.6
3.5
2.8
1.8
1.8
85
46
36
23
23
979
1,808
2,561
678
1,055
11.7
19.4
150
-
5,048
-
ragworm
wedge shell
cockle
nut shell
pipi
mud whelk
top shell
opal shell
grey anemone
Most of Park and Donald’s (1994) sample sites had relatively clean sand with low silt (8.6%),
total organic carbon (0.12 g 100g -1) and nutrient content. These areas were dominated by
wedge shells, cockles and seagrass. The fauna associated with the seagrass was similar to
descriptions from other northern New Zealand harbours (Morton and Miller, 1973). Muddier
areas were characterized by mud snail (Amphibola avellana) communities. Densities of the
dominant species are typical of other harbours and estuaries in New Zealand. For example, the
maximum density of cockles in Tauranga Harbour (2,185 m2) is comparable to the maximum
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density of 2,560 m2 recorded by Knox & Kilner (1973) in the Avon-Heathcote Estuary and by
Murray (1978) in the Maketu Estuary.
Some species showed correlations in density due to one species providing substrate for
another. For example, the cockle provided a hard substrate for the common shore anemone
and pipi provided a hard substrate for the green shield chiton (Chiton glaucus). There were no
highly significant negative correlations between any species that would suggest competition.
There was also no correlation between bivalves and polychaetes, indicating there is little
interaction with changing dominance of species amongst sites (Park and Donald, 1994).
Park and Donald (1994) reported that mean species diversity (number of taxa in each sample)
was 5.3 in bare substrate and 6.2 in seagrass. It is likely a much higher diversity would have
been observed in the seagrass if a smaller sieve mesh size had been used (e.g. 0.05 or 1 mm).
The slightly higher subtidal diversity is likely due to this difference in sieve size (1 mm sieve
rather than 2 mm).
Species diversity showed a strong negative correlation with silt content. The feeding structures
of filter feeding species, such as cockle and nut shell, become clogged when silt levels are
high. Some species, such as the hairy mud crab (Macrophthalmus hirtipes) and a polychaete
worm (Heteromastus filiformis) showed a positive correlation with silt content. The
importance of various parameters (e.g. silt content, total organic carbon, nutrients) varies from
species to species. These results are consistent with Thrush et al. (2003) who developed
models of macrofaunal species occurrence with respect to sediment mud content. Specifically
they found similar responses whereby sensitive species with a preference for low mud content
included the mobile suspension feeding cockle and the deposit and suspension feeding nut
shell. Tolerant species with preferences for higher mud content included mud crabs and the
polychaete worm (H. filiformis).
Rocky Shore
Rocky shores cover less than 0.1% of the total area and perimeter of Tauranga Harbour (Park
and Donald, 1994). The small number of surveys carried out in the hard bottomed
communities at the harbour entrance have indicated these areas are very diverse with high
densities of filter feeding species (Harrison and Grierson and Partners, 1982; Healy et al.,
1991; Healy et al., 1988).
Healy et al. (1988) describes the rocky communities at two dive sites near the southern
entrance to the Tauranga Harbour (outside harbour, near Moturiki and Motuotau Islands). The
intertidal rocks were characterized by barnacles and little black mussels (Xenostrobus pulex)
with bands of brown seaweeds interspersed with clumps of red seaweeds below the low water
mark. The rocky bottom marine life at these sites appeared typical of this type of habitat and
included organisms such as sponges, ascidians, bryozoans, hydroids, sea stars and crabs (Table
13). Green-lipped mussels at one site were large while at the other there was a band of dense
young green-lipped mussels (25-30 mm length) at 5 to 10 m depth, most likely the result of
good settlement the previous spring. The low numbers of sea urchins and crayfish were in
Manaaki Taha Moana Report No. 1
57
keeping with the rest of the coastline with its present level of fishing pressure. The report
concluded that there was no obvious effect on the rocky bottom marine life from previous spoil
dumping operations.
Table 13.
Species observed at two rocky dive sites near the southern entrance to Tauranga Harbour in 1988.
Fish are not included in this table.
Molluscs
Clown nudibranch
Ceratosoma amoena
Limpet
Cellana stellifera
Little black mussel
Xenostrobus pulex
Green-lipped mussel Perna canaliculus
Crustaceans
Barnacle
Chamaesipho brunnea
Barnacle
Chamaesipho columna
Barnacle
Epopella plicata
Crayfish
Jasus edwardsii
Red rock crab
Guinusia chabrus
Algae
Brown algae
Xiphophora chondrophylla
Brown algae
Carpophyllum maschalocarpum
Brown algae
Lessonia variegata
Coralline paint
Corallinales order
Kelp
Ecklonia radiata
Red algae
Pterocladia lucida
Red algae
Vidalia colensoi
Source: (Healy et al., 1988)
Sponges
Black sponge
Boring sponge
Golfball sponge
Golfball sponge
Echinoderms
Cushion star
Eleven-armed seastar
Kina
Reef star
Tennis ball urchin
Other
Hydroids
Anemones
Bryozoans
Ascidians
Zoanthids
Ancorina alata
Cliona celata
Tethya aurantium
Tethya ingalli
Patiriella regularis
Coscinasterias calamaria
Evechinus chloroticus
Stichaster australis
Holopneustes inflatus
Solanderia sp.
Actinothoe albocincta
Hipsistozoa fasmeriana
The rocky reefs surrounding Motuotau Island, although outside the harbour, are of interest as
they are located inshore of the dump ground for dredge spoil from Port of Tauranga
operations. Since 1990, biological monitoring has been carried out to determine the impact of
dumped sediment on the reef biological communities using photographs of permanent
transects and measurements of sediment change (Grace, 1997; Keeley and Pilditch, 1998; Ross
and Pilditch, 2006; Ross and Pilditch, 2009). In concurrence with previous surveys, the most
recent survey (Ross and Pilditch, 2009) showed no major changes to community composition
(Appendix 2) that could be attributable to dredging activities and no significant change in
height of the sediment boundary from 2006. They concluded that, in general terms, the reefs
around Motuotau Island appeared to be healthy and in a state typical of reefs of similar depth,
aspect and exposure found elsewhere on the neighboring coastline.
Customary, Recreational and Commercially Important Species
Gathering shellfish from Tauranga Harbour is not limited to the local population as visitors
come from Auckland, Hamilton, Rotorua and as far south as Turangi to gather (Scholes et al.,
2009). Shellfish beds in the harbour are easily accessible and, due to the calm conditions,
shellfish are collected from here in favour of the open coast (Scholes et al., 2009). The state of
shellfish beds in Tauranga Harbour has not been formally assessed recently, but local people
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have raised concerns over the health status of shellfish species. For example, Britton et al.
(2007) reported the following concerns: horse mussels near Otumoetai have disappeared;
shellfish gathered from particular beds (e.g. Tanners Point and Bowentown) are considered
unsuitable to eat; shellfish beds in some areas (e.g. Waipu Bay and Matahui) are being affected
by recreational activities; cockles are getting smaller and are being depleted by spreading silt
layers. Although there is no consistent agreement with regard to the reasons for these changes,
overfishing or other human activities are thought to be responsible.
In 2006, the Tauranga Moana Iwi Customary Fisheries Management Committee carried out a
survey of customary and traditional fishing practices within Tauranga Harbour (Tata and Ellis,
2006). Macroinvertebrate species mentioned by Tauranga moana kaumatua and kuia are listed
in Table 14 with cockles and titiko (Amphibola avellana) most frequently remarked upon.
Mount Maunganui was identified as a fishing ground with high species diversity having pipi,
kina, crayfish, mussels, crab, paua, catseye, oysters, cockle and tuatua. Other fishing grounds
with high species diversity included Waipu, Poike, the Matakana Channel, Katikati and
Tuapiro.
Table 14.
Macroinvertebrate species mentioned by Tauranga moana kaumatua and kuia
Māori Name
Common Name
Freshwater koura Freshwater crayfish
Kina
Sea urchin
Koura
Crayfish
Kuhara
Freshwater cockle
Kukuroa
Horse mussel
Kutae
Mussel
Papaka
Crab
Paua
Black foot abalone
Source: (Tata and Ellis, 2006)
Māori Name
Common Name
Pipi
Piritoka
Pupu
Tio
Titiko
Tuangi
Tuatua
Tupa
Pipi
Limpet
Catseye
Oyster
Mud snail
Cockle
Tuatua
Scallop
Early quantitative studies that focused on edible shellfish include Bioresearchers (1974a;
Bioresearchers Ltd, 1977a; Bioresearchers Ltd, 1977b; Bioresearchers Ltd, 1977c;
Bioresearchers Ltd, 1984; Bioresearchers Ltd, 1988) and Roan (1989). Bioresearcher’s early
reports (1974b, 1976a) describe edible macroinvertebrates including the mud snails (A.
crenata), pipi (Amphidesma australe / P.s australe), cockles (Chione stutchburyi / A.s
stutchburyi), green-lipped mussels (P. canaliculus) and scallops (P.novazelandiae). Pipi were
recorded in a bed of exceptionally high density near the Bowentown entrance to the harbour.
Otherwise this species occurred in scattered beds throughout the harbour, generally on the
edges of channels (Bioresearchers 1974b). In 1976 the common pipi was recorded to occur
throughout the harbour, reaching greatest densities and largest size in the beds near both of the
harbour entrances. Sublittoral beds occurred in swift flowing channels. Local beds of edible
pipi were recorded towards the centre of the harbour, notably at Omokoroa, and also scattered
in the major channels (Bioresearchers 1976a).
Manaaki Taha Moana Report No. 1
59
Cockles occurred throughout the harbour, but over much of the area did not attain harvestable
size (Bioresearchers 1974b). Very dense beds were reported in the Katikati Harbour region,
particularly near low water on the edges of sand banks near the harbour entrance. Populations
were of low density in seagrass beds (Bioresearchers Ltd, 1976a).
Green-lipped mussel beds were recorded in the channels of the Katikati Harbour region,
however it was reported that little is known of the condition of mussel beds at present
(Bioresearchers 1974b). In 1976 green-lipped mussels were reported to occur in small beds on
the rocky headlands of Mount Mauganui and the northern entrance at Bowentown, as well as
extensive sublittoral beds inside the northern entrance to the harbour (Bioresearchers Ltd,
1976a). The northern beds were a popular source of mussels for food, with mussels being
taken by snorkel diving in shallower areas and dredging from small boats in deeper areas. It
was reported that considerable damage has been done to the beds in some areas due to over
exploitation and that the dense mat of living mussels and shells have been destroyed over large
areas exposing a fine sand bottom unsuitable for attachment by recruiting juveniles
(Bioresearches 1976a). Scallops were apparently scarce in the harbour, with beds being
exploited by scuba diving in the deeper channel regions (Bioresearchers 1974b).
Healy et al. (1988) reported on edible shellfish in the vicinity of port dredging and spoil dump
sites (outside harbour). Shellfish in the dredge zone consisted of moderate numbers of cockles
and a few wedge shells on the shallow sandy flats and some horse mussels in previously
dredged areas. The dump zone contained predominantly juvenile morning star shells (T.
spissa) (~ 5-10 mm long; 2 years old), whereas control sites contained more adults (~ 20 mm
long; 6 years old), suggesting an historical effect from spoil dumping with young morning star
shells only recently recolonizing the area. No scallops were found in the dump zone but few
were seen in control areas either.
As part of Park and Donald’s (1994) benthic macrofauna survey, length-frequency data were
collected for shellfish at the intertidal sites to give an indication of shellfish stocks in the
harbour. Not all beds of edible shellfish were sampled and sampling sites were located at
mean mid and low tide levels, whereas the largest cockles are usually found lower on the shore
and the largest pipi in the shallow subtidal. Cockles from most of the sites were below eating
size (30 mm). Park & Donald (1994) noted that there are a number of areas close to the
harbour entrance with good densities of larger cockles (35 to 50 mm). Cockles, wedge shells
and pipi all showed a trend of larger shellfish near the harbour entrance with progressively
smaller sizes in the upper harbour. Shellfish near the harbour entrances may have better
feeding conditions due to greater food availability and better water quality. Comparison of
cockle length-frequency data from 1974 (Bioresearchers Ltd, 1974b) shows no apparent
change over the 16 year period.
A 1996 survey of pipi on Centre Bank (near the Tauranga entrance to the harbour) found the
species to be widely distributed with densities of up to 1,400 per m2 and shell lengths of 55-65
mm (Hull, 1996). Other common bivalve species in this area were T. spissa and Ruditapes
largillierti.
60
Manaaki Taha Moana Report No. 1
Since 1999, the Ministry of Fisheries (MFish) has monitored cockles and pipi at Otumoetai,
near the southern entrance to Tauranga Harbour, as part of a wider survey of shellfish
populations in northern New Zealand (Pawley, in press). Otumoetai was surveyed in 2001,
2003, 2006, 2007 and 2010 to monitor changes in shellfish abundance and thus to determine if
management measures should be implemented, such as restrictions on harvesting at particular
sites.
Pipi from Otumoetai exhibited a negative trend, with estimated total numbers down by 50% in
2010 compared to the 2006 survey. In contrast, the total number of cockles in 2007 and 2010
was significantly higher (up about 200%) compared to 2006 and earlier surveys, although the
proportion of cockles of harvestable size was low, at around 1%, consistent with previous
surveys (Pawley, in press).
4.2.2. Finfish
Sand flounder, yellow-belly flounder, grey mullet and snapper are commercial fish
species common within the harbour (2009).
Snapper, trevally, kingfish and kahawai caught in Tauranga Harbour are part of larger
Bay of Plenty fish stocks, and move into and out of the harbour (1998).
The harbour is important for spawning and migration of whitebait, short-finned eel,
long-finned eel and lamprey (2009).
Of the 34 fish species recorded in northern New Zealand estuaries, 17 were observed in
Tauranga Harbour (2001).
Ten species of fish were found in the mangroves of Tauranga Harbour, predominantly
small semi-pelagic schooling species, dominated by yellow-eyed mullet, smelt and
short-finned eel (2007).
Aside from grey mullet and short-finned eel, no other commercial fish species were
found in Tauranga’s mangroves (2007).
Total fish and species richness in the mangroves was comparable with most other
northern New Zealand estuaries (2007).
Fish species in the mangroves varied in their response to the forest and physical
environmental variables measured (2007).
Fish species observed in rocky reef habitats are typical of this type of habitat in
northeastern New Zealand (1988).
Tangata whenua have noticed a decline in many fish species (2008).
A range of fish species are found within Tauranga Harbour (Ellis et al., 2008; Environment
Bay of Plenty, 2009a); see Table 15. Amongst these, trevally, sand flounder, yellow-belly
flounder, grey mullet and snapper are common commercial species (Environment Bay of
Plenty, 2009a). The harbour is also important for spawning and migration of whitebait, shortfinned eel, long-finned eel and lamprey (Ellis et al., 2008; Environment Bay of Plenty, 2009a).
Table 15.
Common fish species within Tauranga Harbour.
Common Name
Manaaki Taha Moana Report No. 1
Species
Common Name
Species
61
Bronze whaler sharks
Carcharhinus brachyurus Short-finned eel
Gobies
Gobiidae sp.
Short-tailed stingrays
Grey mullet
Mugil cephalus
Smelt
Herrings
Clupeidae sp.
Snapper
Jack mackerel
Tachurus novaezelandiae Spotted stargazer
Kahawai
Arripis trutta
Spotties
Kingfish
Seriola lalandi
Sprat
Koheru
Decapterus koheru
Tarakihi
Long-finned eel
Anguilla dieffenbachii
Trevally
Long-tailed stingrays
Dasyatis thetidis
Triplefins
Parore
Girella tricuspidata
Yellow-belly flounder
Piper
Hyporhamphus ihi
Yellow-eyed mullet
Sand flounder
Rhombosolea plebeia
Source: (Environment Bay of Plenty, 2009a; Morrisey et al., 2007)
Anguilla australis
Dasyatis brevicaudata
Retropinna retropinna
Pagrus auratus
Genyagnus monopterygius
Notolabrus celidotus
Sprattus sprattus
Nemadactylus macropterus
Pseudocaranx dentex
Tripterygiidae sp.
Rhombosolea leporina
Aldrichetta forsteri
Commercial and recreational fishing
Catch reporting by commercial fishers occurs at a scale that reveals little about the health of
fish stocks in Tauranga Harbour. However, a report by a Fisheries Dispute Commissioner
(Trapski, 1998) about the on-going tensions between recreational and commercial fishing in
Tauranga Harbour provides a good overview of the issues related to finfish abundance in the
harbour.
The Trapski report draws upon MFish (1998) and technical reports from BOPRC as well as
oral submissions, but unfortunately does not provide references for specific statements or facts.
Judge Trapski (1998) reported:
62
Various fishing methods, and all commercial shellfish harvesting, are prohibited in the
harbour at all times, and trawling and Danish seining are prohibited within 2 miles of
the outer shoreline. The commercial fishing within the harbour of most concern is
drag netting, which occurs mostly in tidal channels at low tide and primarily targets
trevally. Snapper is also taken as a bycatch but fishers reported that they mostly return
these to the sea alive.
Over the period 1984 to 1996/97, commercial catches of trevally varied between 23
and 86 tonnes, while commercial snapper harvest fell from 27 tonnes in 1984 to 4.5
tonnes in 1996/97 (Figure 16).
According to boat ramp surveys in 1992, the recreational catch rates in Tauranga
Harbour were among the lowest in the region. Nonetheless, recreational harvest of
snapper as estimated from surveys was, in 1994 and 1996, roughly ten times the
commercial catch, at 46 tonnes in 1996 (Figure 16).
Snapper, trevally, kingfish and kahawai caught in Tauranga Harbour are part of the
larger Bay of Plenty fish stocks, and move into and out of the harbour “so that the
extent of their exploitation in the greater Bay of Plenty waters has a major direct effect
on their population within the harbour” (p.9).
The main reason for trevally and snapper to enter the harbour is to feed. The report
cites several environmental changes in and around the harbour (deforestation and
siltation, black swans and loss of seagrass, an increase in recreational fishing and
noise from boating) that are likely to influence the abundance of fish there, each of
which has had an effect “probably far in excess of that of the operations of drag net
fishers” (p.12).
Manaaki Taha Moana Report No. 1
Trawlers targeting snapper concentrate much of their activity around the northern
entrance to the harbour, in some cases breaching the 2 mile exclusion zone. “It is so
easy to link the intensity of these trawl tows to the lack of abundance of fish at that
end of the harbour and no scientific or other reasoning will shift that perception”
(p.30).
180.0
160.0
140.0
Tonnes
120.0
Snapper-Rec
100.0
Snapper-Com
80.0
Trevally-Com
60.0
40.0
20.0
0.0
1984 1985 1986 1988 1990 1991 1992 1993 1994 1995 1996 1997
Figure 16.
Commercial and recreational catch of trevally and snapper in Tauranga Harbour and Statistical
Area 009. Commercial catch for 1984-86 is from Tauranga Harbour, all methods; data for 19911997 are from statistical area 009 for drag net only. Time series is incomplete due to changes in
catch reporting systems. Recreational catch was estimated in 1984, 1994 and 1996 only, from
occasional surveys of recreational fishers. Source: (MFish, 1998).
In considering various options for reducing the tensions between commercial and recreational
fishers, Judge Trapski noted that banning commercial fishing or indeed all fishing was unlikely
to make a large difference to fish abundance given that very little fish stock is resident in the
harbour. Drag netters did, however, agree to extend voluntarily the closed period for their
activity to the end of February, to provide more opportunity for recreational fishers during
summer months (Trapski, 1998).
Having noted “the strength of the convictions of local people that something must be done”
and “the sheer frustration of local people in seeing that their concerns appear to have been
ignored” (p.24), Judge Trapski’s main recommendation was to change the way the fishery and
the harbour are managed (p.28):
I therefore strongly recommend the devolution of the control of the Tauranga Harbour
fishery to essentially local interests through a co-operative organisation of stakeholders
with contributions from:
Manaaki Taha Moana Report No. 1
63
a.
b.
c.
d.
recreational fishing and boating interests;
local commercial fishing interests
local Māori; and
the Ministry of Fisheries.
This organisation could consider the establishment of taiapure, marine parks and marine
farming in the harbour, the reseeding of lost shellfish beds, the control of adverse
environmental factors, and contracting out of compliance and research, depending on
funding, and take account of all matters of local and regional interest in the harbour.
… I should report that these proposals have met with approval wherever they have been
aired.
Changes to the commercial fishing regulations were gazetted to extend the restrictions on drag
netting and a mataitai for a small area has been approved (see below), but there has otherwise
been no devolution of management as recommended by Judge Trapski.
Surveys of fish species and abundance
There have also been some studies that looked at fish in Tauranga Harbour more specifically.
A fish survey carried out in 25 northern New Zealand estuaries observed a total of 71,211 fish
representing 34 species; 17 of these occurred in Tauranga Harbour (Francis et al., 2005).
Yellow-eyed mullet (Aldrichetta forsteri) was the most abundant species overall, present at
90% of the sampling stations and accounting for 42% of the total catch by number.
A study of fish assemblages of temperate mangrove forests of northern New Zealand surveyed
eight estuarine mangrove systems: Kaipara, Manukau, Rangaunu, Mangawhai, Mahurangi,
Waitemata, Whangapoua and Tauranga (Morrisey et al., 2007). A total of 17,327 fish
representing 19 species were collected during the survey; 98% were juveniles. Ten species of
fish were identified in the mangroves of Tauranga Harbour and of these approximately 96%
were small semi-pelagic schooling species (mullets, smelt and sprat). The dominant species
was yellow-eyed mullet, followed by smelt (Retropinna retropinna) and short-finned eel
(Anguilla australis). Except for short-finned eel and grey mullet (Mugil cephalus), no other
commercial species (e.g. snapper, jack mackerel, kahawai) were found in Tauranga Harbour
mangrove habitat. Total fish and species richness within Tauranga Harbour was comparable
with the other estuaries, except Rangaunu and Mahurangi, which showed greater richness, and
Manukau, which was higher in both total fish and richness.
The species found in the mangrove study varied in their response to the forest and physical
environmental variables measured (Morrisey et al., 2007). Yellow-eyed mullet were positively
associated with increasing distance from the sea, and grey mullet and yellow-belly flounder
(Rhombosolea leporina) were strongly positively associated with total suspended sediments.
Short-finned eels were positively associated with increasing mangrove habitat complexity
(seedlings, saplings, and number of trees), while parore (G. tricuspidata) were associated with
higher water clarity and intermediate sediment grain size.
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Manaaki Taha Moana Report No. 1
Healy et al. (1988) recorded 27 species of fish at two rocky dive sites close to the southern
entrance of Tauranga Harbour (outside harbour, near Moturiki and Motuotau Islands) (Table
16). These species are typical of rocky reef habitats in northeastern New Zealand and, while
the authors note that the list is not comprehensive, it contains all the common species likely to
be observed by diving in the area. The absence of snapper (P. auratus) is most likely due to
the shy nature of this species and although snapper numbers were most likely down on natural
stocks like other areas along the northeastern coast, they were probably present around the
reefs.
Table 16.
Fish species observed at two rocky dive sites near the southern entrance to Tauranga Harbour in
1988.
Common Name
Species
Banded wrasse
Notolabrus fucicola
Bigeye
Pempheris adspersa
Blue cod
Parapercis colias
Blue-eyed triplefin
Notoclinops segmentatus
Blue maomao
Scorpis violacea
Butterfish
Odax pullus
Conger eel
Conger sp.
John dory
Zeus faber
Jack mackerel
Trachurus novaelandiae
Kelpfish
Chironemus microlepis
Leather jacket
Parika scaber
Marblefish
Aplodactylus arctidens
Masked triplefin
Parore
Girella tricuspidata
Source: (Healy et al., 1988)
Common Name
Red-banded perch
Red moki
Red mullet
Rock cod
Roughy
Scaley-head triplefin
Scorpionfish
Spotty
Sweep
Topknot blenny
Trevally
Variable triplefin
Yaldywn’s triplefin
Species
Hypoplectrodes huntii
Goniistius spectabilis
Upeneichthys lineatus
Lotella rhacina
Trachichthyidae sp.
Karalepis stewarti
Scorpaenidae sp.
Notolabrus celidotus
Scorpis lineolatus
Notoclinus fenestratus
Pseudocaranx dentex
Forsterygion varium
Notoclinops yaldwyni
Tauranga Harbour is an important traditional resource supplying the nutritional needs of local
people that live close by. Three forms of fishing exist within the harbour: commercial,
recreational and customary. In 2007 there were approximately 6 drag netting licenses in
existence but these are being phased out over time as they expire or are no longer used (Britton
et al., 2007); only one commercial fisher is still operating inside the harbour in 2011 (D & B
Kiddie, pers. comm.). Recreational fishing is popular within the harbour (Figure 17) but there
is no obligation for recreational fishers to report their catch, so data on recreational fishing are
sparse. In 2007, a survey recorded an average of 36 boats fishing in the harbour at any one
time during daylight hours, on weekends and holidays (Britton et al., 2007). The Tauranga
Moana Customary Fisheries Committee receives reports on fish taken from authorised
customary fishers, but this information has not been compiled or published. Interviews with
kaumatua and kuia of Tauranga moana identified Motiti Island (outside southern entrance to
harbour), Tuapiro, Tuhua, Katikait, the Wairoa and Waimapu Rivers and Waipu as fishing
grounds with high fish species diversity (Table 17) (Tata and Ellis, 2006). Snapper, flounder
and kahawai were the fish species most frequently mentioned in the interviews.
Manaaki Taha Moana Report No. 1
65
Tangata whenua have noticed a decline in many fish species including flounder, shark,
snapper, kingfish, trevally and mullet (Ellis et al., 2008; Tata and Ellis, 2006). Although many
do not attribute the decline in fish directly to commercial fishing, they believe there is a
correlation between the two. They have raised concerns over the amount of bycatch being
wasted by commercial fishers and fishing methods, such as drag netting, which they believe to
have adverse effects on benthic habitat comparable to scallop dredging (Ellis et al., 2008).
Tangata whenua have expressed a desire for all forms of commercial fishing to be banned
within the harbour to allow the replenishment of fish stocks (Ellis et al., 2008).
A commercial fisher has also noted changes in fish communities. Parore used to be so
numerous that it was considered a nuisance, but now is rarely caught inside the harbour.
Species such as trevally and snapper, which move into and out of the harbour, are still plentiful
(D & B Kiddie, pers. comm.).
A number of commercial fishing methods are prohibited in Tauranga Harbour, including box
or teichi net, purse seine net, Danish seine net, trawl net, lampara net, and set nets longer than
1000 m. In addition, no new permits are being issued for dragnetting inside the harbour (New
Zealand Government, 2011).
Figure 17.
66
Recreational fishing on Tauranga Harbour (photo: Noel Peterson).
Manaaki Taha Moana Report No. 1
Table 17.
Fish species observed by Tauranga moana kaumatua and kuia in seven fishing grounds in and
around Tauranga Harbour. ‘X’ indicates presence at fishing ground.
Māori
Common
Name
Name
Araara
Trevally
Aua
Herring
Barracuda
Barracuda
Blue Moki Blue Moki
Hake
Frost Fish
Hapuka
Bass Grouper
Inanga
Whitebait
Kahawai
Kahawai
Kanae
Mullet
Kehe
Marblefish
Koeaea
Butterfish
Kokiri
Leatherjacket
Kuparu
John Dory
Maomao
Maomao
Marlin
Marlin
Paketi
Spotty
Parore
Black snapper
Patiki
Flounder
Pioke
Shark
Rawaru
Blue cod
Sunfish (non-target)
Tamure
Snapper
Taraute
Trout
Tuna
Eel
Wahi
Stingray
Wheke
Octopus
Yellowfin
Yellowfin
Tuna
Tuna
Total fish species
Source: (Tata and Ellis, 2006)
Motiti
Island
Tuapiro
Tuhua
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Wairoa
River
Waipu
Waimpau
River
Katikati
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
12
X
X
X
X
X
X
X
X
X
X
11
10
9
X
X
X
14
12
12
In 2008, the Te Maunga o Mauao Mataitai Reserve was established over 6 km2 around Mt
Maunganui (Figure 18). This area excludes commercial fishing and enables the Tauranga
Moana Customary Fisheries Committee to advise the Minister on how best to manage fishing
within the area. Within the mataitai, the recreational bag limit for mussels has been reduced
from 50 per person to 25.
Manaaki Taha Moana Report No. 1
67
Figure 18.
Area of mataitai fisheries reserve indicated by blue line around Mount Maunganui. Source:
(MFish, 2008).
4.2.3. Marine mammals
New Zealand fur seals are common visitors to the harbour and leopard and elephant
seals are occasionally sighted (2011).
More than 30 cetacean species have been observed in the Bay of Plenty and at least 8
species seen within the harbour (2011).
Detailed information regarding seasonality and frequency of cetacean visits to Tauranga
Harbour is not available (2011).
Several large marine mammals are known to frequent Tauranga Harbour, including seals,
dolphins and whales (Ellis et al., 2008). The New Zealand fur seal (Arctocephalus forsteri) is
a common visitor to the area and leopard seals (Hydrurga leptonyx) and elephant seals
(Mirounga leonina) are occasionally sighted (DOC, 2009; Knill, 2009; Lodi News-Sentinel,
1987; The World, 1987). Tauranga moana kaumatua and kuia report sightings of seals at
Katikati and the Waimpu River, sea lions at Tuapiro and walruses at the Waimpu River (Tata
and Ellis, 2006). More than 30 cetacean species have been observed around the waters of Bay
of Plenty and at least eight species have been observed within Tauranga Harbour (DOC,
2010a; DOC, 2010b). Detailed information regarding the frequency and seasonality of those
cetaceans that may visit the harbour is not available. The current knowledge for a few of the
more commonly sighted species is summarised below relative to their New Zealand status in
order to place the Tauranga situation in context.
The common dolphin (Delphinus delphis), found around much of the New Zealand coastline,
is often sighted within Tauranga Harbour. These dolphins are well known on the eastern side
of the North Island, in the Bay of Islands (Constantine and Baker, 1997), Hauraki Gulf
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Manaaki Taha Moana Report No. 1
(Stockin et al., 2008a) and Bay of Plenty (Neumann et al., 2002), but are also regularly sighted
as far south as Kaikoura (Wursig et al., 1997). Common dolphins are often sighted in large
schools of 200-400 individuals (Neumann and Orams, 2005) but reported as large as 1000
(DOC, unpublished data) in the waters of Bay of Plenty. Despite their commonality, very little
is known about their population size or regular movement patterns (Dawson, 1985). They are
an active species known to have a more pelagic distribution and an affinity for following warm
water currents, such as the subtropical East Cape Current and thermoclines. Common dolphins
are considered not threatened in New Zealand (Baker et al., 2010) but are known to be
affected by tourism, fisheries bycatch and pollutants (Du Fresne et al., 2007; Stockin and
Orams, 2009; Stockin et al., 2008b). Stranding data from the DOC database show that
individual common dolphins occasionally strand within Tauranga Harbour.
Bottlenose dolphins (Tursiops truncatus) are also known to visit Bay of Plenty waters. In New
Zealand this species inhabits the coastal waters of Northland, the Marlborough Sounds and
Fiordland, with occasional sightings of animals around most other regions (Baker et al., 2010;
Tezanos-Pinto et al., 2008). These three distinct regional populations show evidence of high
genetic differentiation between them with very low rates of estimated migration. The
Northland population is primarily found between Doubtless Bay (on the east coast of
Northland) and the Coromandel Peninsula, including the Bay of Islands, but occasionally
ranges from Tauranga to Manukau (Baker et al., 2010). While bottlenose dolphin populations
overseas are considered to be relatively stable, this species is listed as nationally endangered in
New Zealand due to the small region and total abundance, and evidence of local decline in two
populations (Baker et al., 2010). Bottlenose dolphin populations in New Zealand are exposed
to a growing eco-tourism industry throughout their range (Constantine et al., 2003) in addition
to being occasionally reported as bycatch in the New Zealand trawl fishery (Du Fresne et al.,
2007).
Another species that regularly visits Tauranga Harbour is the killer whale, or orca (Orcinus
orca) (DOC unpublished information). A study by Visser (2000) suggested that the New
Zealand orca population is probably comprised of three sub-populations: a North Island
population, a South Island population and a population that travels between the two islands.
The earliest record of orca visits to Tauranga Harbour was in 1915, where three individuals
entered Tauranga Harbour and were driven ashore and killed by local whalers (Visser, 2000).
More recently the Bay of Plenty Times reported observations of four orcas in the harbour
(Irvine, 2010) and Tauranga moana kaumatua and kuia reported orca sightings at Katikati,
Tuapiro and Tuhua (Tata and Ellis, 2006). Despite the general lack of harbour sightings, the
east coast of the North Island appears to be an important region for both the North Island and
the North-South Island sub-populations (Visser, 2000). They appear to be more frequent in
these waters during winter and spring months and are usually found further offshore (~10-80
nautical miles) over winter months (Clement, 2010). Bay of Plenty waters may represent an
important feeding habitat for these animals based on opportunistic sightings (Clement, 2010).
This species is listed as one of New Zealand’s nationally critical marine mammal species, due
to an extremely low population estimate of less than 200 animals (Clement 2010).
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Other cetacean species recorded in and around Tauranga Harbour include blue whale
(Balaenoptera musculus), sei whale (Balaenoptera borealis), minke whale (Balaenoptera
acutorostrata), long-finned pilot whale (Globicephala melaena), southern bottlenose whale
(Hyperoodon planifrons), pygmy sperm whale (Kogia breviceps), Gray’s beaked whale
(Mesoplodon grayi), Cuvier’s beaked whale (Ziphius cavirostris) and rough-toothed dolphin
(Steno bredanensis) (DOC, 2010a; DOC, 2010b). Tauranga moana kaumatua and kuia have
reported observations of dolphins at Waipu, Maungatapu, Rereatukahia, Katikati, Tuapiro and
Motiti and whale sightings at Rangataua Bay, Maungatpau, Tuhua and Motiti Island (Tata and
Ellis, 2006).
4.2.4. Birds
Birds identified around Tauranga Harbour include 20 endemic species, 28 native species,
8 migrant species and 15 introduced species (2011).
Nationally critical birds that visit the harbour include black stilt, grey duck and white
heron (2008).
Nationally endangered birds that visit the harbour include bittern and black-billed gull
(2008).
Nationally vulnerable birds that visit the harbour include banded dotterel, caspian tern,
New Zealand dabchick, pied shag, reef heron, wrybill, northern New Zealand dotterel
and red-billed gull (2008).
Tauranga Harbour is recognized as a wetland of international significance for the
protection of migratory and indigenous wetland bird species (2003).
Increasing coastal pressure can be detrimental to bird species that use the harbour (2006).
Tauranga Harbour has the highest number of shorebirds in the Bay of Plenty region
(2006).
Wading bird species show mixed population trends over 1984-2010 (2010).
During summer Matakana Island hosts the largest breeding population of northern New
Zealand dotterel in the country and a large post-breeding flock of this species during the
winter (2006).
Mount Maunganui hosts one of the few remaining mainland colonies of both grey-faced
petrel and blue penguin (2011).
There was a significant increase in Canada geese over 2001-2010 (2010).
The wider Tauranga catchment is home to many birds (see Shaw et al. 2010 for a summary of
historic and current avifauna in the area) but this summary focuses only on birds that use
Tauranga Harbour. A number of bird surveys have been carried out around Tauranga Harbour
(Beadel et al., 2003b; Ellis et al., 2008; Greenway et al., 2006; OSNZ, 2010; Owen et al.,
2006). Of the bird species recorded, 20 are endemic (species that occur only in New Zealand),
28 are native (species that naturally occur in New Zealand but are also found in other
countries), 8 are migrant (regular bisitors but do not breed in New Zealand) and 15 are
introduced (species that are not naturally found in New Zealand and have been introduced by
humans) (Appendix 3).
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Nationally critical birds that visit the area include the black stilt, one of New Zealand’s rarest
shorebirds; the grey duck, which has experienced a greater than 70% population decline over
three generations; and the white heron, for which predation and changes in land use are
suggested to be the main causes for its nationwide deterioration in conservation status
(Hitchmough et al., 2007; Miskelly et al., 2008) (Table 18). Other threatened birds that visit
Tauranga Harbour include the Australasian bittern and the black-billed gull (both nationally
endangered) and eight species of nationally vulnerable birds. Changes in ocean productivity,
possibly linked to global warming, have been suggested to be the main cause for the red-billed
gull’s drop in status from gradual decline to nationally vulnerable (Miskelly et al., 2008).
A field survey, conducted on the Waikaraka Estuary Restoration Area (within Tauranga
Harbour), identified 30 bird species of which 19 were indigenous (Beadel et al., 2003b). The
nationally vulnerable red-billed gull was abundant, as was the New Zealand kingfisher
(Todiramphus sanctus vagans), white-faced heron (Ardea novaehollandiae), and black-backed
gull (Larus dominicanus), while pied oystercatcher (Haematopus finschi, NZ conservation
status declining), pied stilt (Himantopus himantopus leucocephalus, NZ conservation status
declining) and tui (Prosthemadera novaeseelandiae novaeseelandiae) were less common
(Beadel et al., 2003b). The only other threatened species (as per Hitchmough 2002) recorded
during the survey were the North Island fernbird (Bowdleria punctata vealeae; 2008
conservation status declining), white-fronted tern (Sterna striata striata; 2008 conservation
status declining) and grey duck (2008 conservation status nationally critical).
Tauranga Harbour meets the criteria of the Ramsar convention (Convention on Wetlands of
International Importance, especially as Waterfowl Habitat) as being a wetland of international
significance for the protection of migratory and indigenous wetland bird species (Beadel et al.,
2003a). However, no application has yet been submitted to the Department of Conservation
seeking listing and ultimate ratification by the RAMSAR Bureau of this status (Owen pers.
comm.). Nevertheless, this internationally important site recognition is based on the criteria
that the area regularly supports one percent or more of the population of a species or
subspecies of shorebird (Owen et al., 2006). The species meeting this criteria in Tauranga
Harbour include: bar-tailed godwit (Limosa lapponica baueri; 5% summer population), black
stilt (4 to 6% winter population), northern New Zealand dotterel (2.6% summer and 1.4%
winter), turnstone (Arenaria interpres; 2.5% summer), banded dotterel (1.7% winter), wrybill
(1.7% winter), variable oystercatcher (H. unicolour; 2.2% summer and 1.7% winter) and pied
stilt (1.5% winter) (Owen et al., 2006).
Over the last three decades increased leisure time has led to increasingly widespread
recreational pressure on New Zealand’s coasts and estuaries (Owen et al., 2006). These
pressures, along with ever-increasing coastal development, are of major concern for
safeguarding nationally and internationally important breeding, migrant and wintering
shorebirds which depend upon these places as a habitat (Owen et al., 2006).
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Table 18.
Conservation status of threatened birds (Miskelly et al., 2008) around Tauranga Harbour.
Common, Māori and scientific names. Photos top to bottom: black stilt, black-billed gull, Caspian
tern, wrybill.
Nationally Critical
Black stilt
Grey duck
Kaki
Parera
White heron
Kotuku
Himantopus novaezelandiae
Anas superciliosa
superciliosa
Ardea modesta
Nationally Endangered
Australasian bittern
Black-billed gull
Matuku
Tarapunga
Botaurus poiciloptilus
Larus bulleri
Nationally Vulnerable
Banded dotterel
Tuturiwhata
Charadruis bicinctus
bicinctus
Hydroprogne caspia
Poliocephalus rufopectus
Phalacrocorax varius
Egretta sacra sacra
Anarhynchus frontalis
Charadrius obscurus
aquilonius
Larus novaehollandiae
scopulinus
Caspian tern
New Zealand dabchick
Pied shag
Reef heron
Wrybill
Northern New Zealand
dotterel
Red-billed gull
Taranui
Weweia
Karuhiruhi
Matuku moana
Ngutuparore
Tuturiwhata
Tarapunga
For example, wading birds forage over inter-tidal flats and harbours, estuaries and soft
sediment beaches at low tide. At high tide – when their feeding grounds are covered by water
(up to six hours, twice daily) – they gather in flocks at specific sites called ‘high tide roosts’
(Owen et al., 2006). Wading birds need the option of several high tide roosts to minimize the
effects of adverse weather conditions, wind direction, timing, height of tide, overlap of habitat
with non-breeding migratory birds and human and other animal disturbances (Owen et al.,
2006). An increase in coastal development can result in reduction in size or complete loss of a
high tide roosting site. When this happens, these birds will still attempt to use such sites, often
to their detriment (Owen et al., 2006). The Sulphur Point reclamation site for port development
was the principal roost site for most shorebirds on the southern half of Tauranga Harbour
(Owen et al., 2006). There are currently 25 known roosting sites in Tauranga Harbour (Owen
et al., 2006).
Owen et al. (Owen, 1993) surveyed marshland bird habitats and populations within Tauranga
Harbour (140 sites). The birds surveyed rely heavily on marshes for their habitat requirements
and included the Australasian bittern, banded rail, spotless crake (Porzana tabuensis plumbea),
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marsh crake (P. pusilla affinis) and North Island fernbird (Owen, 1993). Thirty-three bird
species were recorded (5 endemic, 15 native, 7 migrant and 6 introduced) and the survey
showed that Tauranga Harbour is nationally significant for Australasian bittern, North Island
fernbird and banded rail and important for Australasian harrier (Circus approximans), New
Zealand kingfisher and pukeko (Porphyrio melanotus). Reclamation (infilling), drainage,
rubbish dumping, livestock grazing, residential or recreational activities, establishment of
public utilities and adventives plants were considered to be the greatest threats to the future
welfare of these marshland bird habitats (Owen, 1993). Owen recommended biannual
monitoring on a harbour-wide scale and a follow-up survey in 2003, however, this has not
occurred (Owen pers. comm.).
The Ornithological Society of New Zealand (OSNZ) has been counting wading bird species
around Tauranga Harbour biannually since 1984. Of the eleven wading bird species studied,
four showed an increasing population trend, five showed a decreasing trend, pied stilt showed
a mixed trend and Pacific golden plover (Pluvialis fulva) numbers were too small to show a
trend (Table 19) (Owen et al., 2006). During summer, Matakana Island (barrier island in
Tauranga Harbour) hosts the largest breeding population in the country of the nationally
vulnerable northern New Zealand dotterel and a large post-breeding flock of this species
during the winter (Owen et al., 2006). Dotterel numbers have increased significantly over the
period 1984-2003, thought to be attributable to a protection programme in place on Matakana
Island (Owen et al., 2006). Numbers have decreased at all other monitored sites in the Bay of
Plenty, but there were too few birds to analyse statistically (Owen et al., 2006).
Mount Maunganui, at the Tauranga entrance to the harbour, hosts one of the few remaining
mainland colonies of grey-faced petrel (Pterodoma macroptera gouldi). Research that began
in 1990 indicates that the Mount Maunganui petrel population is stable (Goodchild, 2001),
although introduced predators such as rats and mustelids still pose a significant threat
(Vaughton, 2001), heightened by the petrel’s very low rate of intrinsic population growth
(maximum of one chick per pair per year) (Miskelly et al., 2009). Chick survival rates pre and
post pest control have been calculated at 20% and 70% respectively (Vaughton, 2001).
Mount Maunganui is also home to a colony of blue penguins (Eudyptula minor) with a
relatively large population size (Jervis and Davies, 2001). A 2000-2001 mark-recapture study
of 106 penguins yielded a recapture rate of just under 30% (Jervis and Davies, 2001). Jervis
and Davies (2000) reported there were no indications that the Mount Maunganui population
were suffering from predation (at the time), although rats, a cat and a mustelid were observed
in the study area.
Fish and Game New Zealand reports on population trends for black swan (Cygnus atratus),
Canada geese (Branta canadensis) and paradise shelduck (Tadorna variegata) (Eastern Region
Fish and Game Council, 2010). Over a wide area that encompasses part of the South Waikato
District as well as all of the Bay of Plenty (Fish and Game New Zealand, 2011), there was a
significant increase in Canada geese for the period 2001-2010, and an insignificant decline of
paradise shelduck and black swan (Eastern Region Fish and Game Council, 2010).
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Table 19.
Population trends (1984-2010) of eleven wading bird species in Tauranga Harbour.
Species
South Island pied oystercatcher
Population Trend 1984-2010 for
Tauranga Harbour
Significant increasing trend for both
summer and winter counts
Additional Comments
Tauranga Harbour is one of four
key habitats in the Bay of Plenty.
Haematopus ostralegus finschi
Variable oystercatcher
General increasing trend for the
whole harbour, but a decreasing
trend for the winter population at the
Sulphur Point roost. Significant
increasing trend for the Matakana
Island population.
Total (world) population is 4,000
(as of 1999). Protection
programme operating on Matakana
Island.
General decrease for winter
population 1984-2001, but an
increase 2006-2010; too few bids to
analyse for summer population.
New Zealand population ~30,000
(as of 1996). General decrease
Bay of Plenty wide over study
period, especially the winter
populations.
Overall increase, but a decrease for
both summer and winter populations
at both the Panepane Point roost (due
to coastal erosion and human
disturbances) and Sulphur Point
roost (due to port development).
Nationally vulnerable species; total
population 1,700 as of 2004.
Protection programme on
Matakana Island. Significant
decrease at all other Bay of Plenty
sites studied.
Decrease across the harbour for both
summer and winter counts,
significantly so at Sulphur Point.
Tauranga Airport has become an
important winter feeding area for
birds displaced from Sulphur Point.
This is a concern because the
Tauranga Airport Authority has had
to ‘control’ the numbers of some
shore birds to maintain public safety
and safe aircraft movements.
Nationally vulnerable species.
National total of 50,000 as of 1996;
numbers have declined
substantially over the past 25 years.
Tauranga Harbour is a notable
winter flocking site.
Haematopus unicolor
Pied stilt
Himantopus himantopus
leucocephalus
Northern New Zealand dotterel
Charadrius obscurus aquilonius
Banded dotterel
Charadruis bicinctus bicinctus
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Wrybrill
Summer counts too few to analyse,
winter counts show a significant
decrease 1984-2001 for the harbour
as a whole, and also at the Sulphur
Point roost. However, numbers
recorded post 2006 have been higher
than previous counts.
Nationally vulnerable species.
National population 4,100 as at
2005.
No winter birds; too few birds in
summer to analyse. Possible that
their main roost(s) is/are yet to be
found.
Arctic migrant; summers
throughout NZ. Bay of Plenty
wide, numbers generally remain
static over the summer counts.
Too few birds to analyse; but there
has been a general increase in
numbers.
Self-introduced from Australia in
1930s. Bay of Plenty wide has an
overall significant increase in
numbers
Winter population too small to
analyse. Summer populations have a
significant decrease over time.
Migratory bird. NZ population
between 5,000 and 7,000. Bay of
Plenty wide there is also a
significant decline in summer
counts.
No winter birds. Summer counts
were too few to analyse, but numbers
have declined from 1984-2003.
Migrant from Siberia. Each year
between 51,000 and 67,400 come
to NZ.
Winter counts too few to analyse.
Summer population trends show a
significant overall decrease 19842003.
An estimated 102,000 birds
migrate to NZ annually. Travel
11,000 km in seven days.
Tauranga Harbour hosts the largest
summer population of godwit in
the region.
Anarhynchus frontalis
Pacific golden plover
Pluvialis fulva
Spur-winged plover
Vanellus miles novaehollandiae
Turnstone
Arenaria interpres
Knot
Calidris canutus rogersi
Bar-tailed godwit
Limosa lapponica baueri
Source: (OSNZ, 2010; Owen et al., 2006)
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4.3. Invasive species
A Port of Tauranga survey found twelve non-native marine species including three that were
new to New Zealand (2002).
Nine of the twelve non-native species recorded are likely to have been introduced via hull
fouling, and the other three could have been introduced via either ballast water or hull fouling
(2002).
Four noteworthy non-native species found in Tauranga Harbour are the Asian date mussel
(Musculista senhousia), the sea squirt Didemnum vexillum, Asian kelp (Undaria pinnatifida) and
a dinoflagellate (Alexandrium tamarense) (2002).
The sea squirt Styela clava is well established in the Hauraki Gulf and is a potential threat to
Tauranga Harbour because of the amount of vessel traffic between the two areas.
The Port of Tauranga does not have substantial numbers of invasive species, and those that are
present have not yet caused significant ecological, social or economic harm (2011).
The extent of spread beyond the port environment is unknown but there are no indications of
invasive species causing significant problems in the wider harbour (2011).
Being home to an active international port, Tauranga Harbour has seen the arrival of a number
of non-native species. Some non-native species appear to be relatively benign, in that
infestations are localised and do not cause significant adverse impacts, while others are
considered “invasive” because they can reach high levels of infestation and have the potential
to be detrimental.
The Port of Tauranga was surveyed for non-native species in 2002 and 2005 for MAF
Biosecurity New Zealand (Inglis et al., 2006; Inglis et al., 2008). The surveys targeted the Port
of Tauranga, because that is the most likely point of introduction to the region. Additional
non-native species could be present in other parts of the harbour that were not surveyed.
The 2002 survey found twelve non-native marine species, including three that were new to
New Zealand. According to Inglis et al. (2006), nine of the twelve non-native species found in
2002 are likely to have been introduced via hull fouling, and the other three could have been
introduced via either ballast water or hull fouling.
The more noteworthy of non-native species that have been found in Tauranga Harbour are
described below, along with another species that is present in the Hauraki Gulf.
Asian Date Mussel
The Asian date mussel (Musculista senhousia) (Figure 19) has
been found in Tauranga Harbour (Environment Bay of Plenty,
n.d.). Native to Japan, the mussel is a well-known fouling
organism and could be dispersed in ballast water. The mussel
forms large mats, which have been known to suppress the growth,
richness and abundances of other species in the vicinity of the
mats, in comparison to areas of substrate without mats (Creese et Figure 19. Asian Date mussel.
al., 1997). A survey of Tauranga Harbour in 2006/07 detected
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mats of Asian date mussel in four locations (Environment Bay of Plenty, n.d.).
Didemnum
Didemnum vexillum (Figure 20) is a filter-feeding sea squirt,
whose colonial growth form can quickly smother marine habitats.
Sea squirts have a planktonic (i.e. mobile) larval life stage but
then adhere to hard surfaces as adults. Didemnum vexillum is
considered crypotogenic because it has not been firmly
established whether it is native to New Zealand (Coutts and
Forrest, 2007). The sea squirt has the potential to out-compete
other species and to smother mussels growing on longlines.
This sea squirt is established in Tauranga Harbour (Environment Figure 20. Didemnum
Bay of Plenty, n.d.). The barge Steel Mariner, which was in vexillum.
Tauranga Harbour in May 1992 and late June 2000, was
identified as the most likely vector for the spread of this sea
squirt to a bay in the Marlborough Sounds from where it was
spread across the top of the South Island (Coutts and Forrest, 2007).
Asian Kelp Undaria
The Asian kelp (Undaria pinnatifida) (Figure 21) has been in
New Zealand since 1987 and is found in most New Zealand ports.
This kelp has the potential to out-compete native species, although
it tends to do better in colder climates, e.g. South Island and lower
North Island, and its spread outside port environs has been limited
(Sinner et al., 2000). It was first found in Tauranga Harbour in
2005 and has been found on shell banks inside the harbour
entrance and on man-made structures at the southern end of the Figure 21. Undaria pinnatifida.
port wharves (Environment Bay of Plenty, n.d.).
Dinoflagellate Alexandrium tamarense
A survey undertaken in 2005 (reported in Inglis et al., 2008) found
the dinoflagellate Alexandrium tamarense. This species produces a
toxin that can cause paralytic shellfish poisoning and is listed on the
Australian Ballast Water Management Advisory Council’s schedule
of non-indigenous pest species (Inglis et al., 2008).
Clubbed tunicate Styela clava
In terms of potential threats, the clubbed tunicate (Styela clava)
(Figure 22) is a sea squirt of particular concern. It is a fouling
organism with the potential to displace native species and smother Figure 22. Styela clava.
aquaculture lines and other structures. Styela clava is well
established in the Hauraki Gulf (Environment Bay of Plenty, n.d.)
and is a potential threat to Tauranga Harbour because of the amount
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of vessel traffic between the two areas.
Based on present information, the Port of Tauranga does not have substantial numbers of
invasive species, and those that are present have not yet caused significant ecological, social or
economic harm. The extent of spread beyond the port environment is unknown, because the
surveys have targeted the port environment only, but there are no indications of invasive
species causing significant problems in the wider harbour. There is, however, the potential for
new species to be introduced from overseas and also within New Zealand via commercial
shipping, aquaculture equipment and recreational vessels.
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5.
Conclusions and research recommendations
5.1. The health of Tauranga Harbour
Based on the limited recent scientific evidence describing the overall condition of the harbour,
the indications are mixed. Time series data is available only since the early 1990s and does not
reveal any significant trends for nutrients and benthic communities.
Changes in the extent of seagrass beds in the harbour, however, are of particular concern.
Seagrass, which covered 22% of the harbour area in 1959, had declined significantly by 1996,
by which time it covered only 14%. The area of inter-tidal beds declined by 27%, and sub-tidal
beds lost 90% of their area during this period; their fate since then is unknown (see section
4.1.3). Seagrass beds enhance food production and nutrient cycling, stabilize sediment, protect
the coast from erosion and support a number of animals and plants. They also provide a
nursery habitat for juvenile fish.
Such a significant reduction in seagrass is a cause for serious concern. Sedimentation and
nutrient loading have been implicated as the main factors in Tauranga Harbour. More research
is needed to confirm this, especially as there are predictions of increasing sediment loads in the
coming decades due to climate change.
Sedimentation rates in Tauranga Harbour are reported to be relatively low compared to other
North Island estuaries but sedimentation has nonetheless been linked to expansion of
mangroves, as well as seagrass decline, and is almost certainly causing other changes to
harbour ecology. Changes to fish and shellfish abundance have been noted anecdotally but
there is no time series data with which to assess the extent of change.
In summarising the current knowledge about the ecological health of Tauranga Harbour from a
western science perspective, a number of information gaps have become apparent. While
studies have been conducted on a wide range of topics, understanding of the overall processes
that drive the estuarine ecosystem is far from complete. In the remainder of this report we
describe key scientific gaps and priorities for future research.
5.2. Broad scale survey
The spatial scale over which information has been collected varies greatly from one study to
the next, reflecting the diverse purposes for which specific studies were undertaken. For
example, sediment loading into the Tauranga Harbour has been determined from both
modelling studies and a field sampling programme to record actual sediment grain size at
varying sites within the estuary. In order to understand sediment within the overall harbour,
that study was conducted over large spatial scales. Conversely, to determine nutrient and
pollutant levels within the harbour, sampling has targeted specific sites, such as stormwater
drains, to assess heavy metals. Thus, the regional council’s nutrient monitoring programme
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has limited spatial coverage: 16 streams and 18 estuarine sites aimed at detecting elevated
nutrient levels flowing into the estuary via riverine systems.
The spatial scale of sampling of flora and fauna within the harbour also varies greatly.
Intensive research has been carried out on the macroalgae communities adjacent to the Port of
Tauranga as part of a nation-wide biosecurity monitoring programme. Because of its limited
extent, such surveys can only provide an indication of what species might be present elsewhere
in the harbour. Macroinvertebrate sampling has been carried out over extensive spatial scales
whereby 160 intertidal sites and 16 subtidal sites were sampled across Tauranga Harbour in
1994. While this information is useful, it is dated and the sieve size varied between the
intertidal and subtidal sampling programmes. Diversity indices are therefore not comparable
between the two data subsets. BOPRC now monitors benthic macrofauna at 17 sites in and
around Tauranga Harbour, to assess benthic community health and detect trends over time
with respect to the integrity of ecosystems. To summarize, while studies have been conducted
on a wide range of topics, studies that assess biodiversity of flora and fauna at the scale of the
estuary have not been conducted.
In order to understand the role of various anthropogenic stressors on biodiversity, we
recommend conducting a broad scale survey of Tauranga Harbour. This would involve
sampling flora and fauna over the larger spatial scale of the estuary and collecting associated
sediment samples to quantify sedimentation, nutrients and pollutants at each site. Sampling
could be conducted over a range of habitats from intertidal sandflats (a key habitat for
shellfish) and mangrove habitats, to subtidal and seagrass areas. Macroinvertebrates would be
assessed at each site using benthic core samples and quadratic information would be collected
to quantify the presence of flora including macroalgae, seagrasses and sea lettuce.
A broad scale survey would provide more current and detailed information to quantify
macroinvertebrate communities, biodiversity and the presence or loss of functional groups
such as shellfish species across the harbour. The collection of physical data at the same sites as
biological data enables changes in community composition to be linked with changes in key
anthropogenic stressors such as sediments, nutrients and pollutants. Specifically the
environmental variables can be used in a model to find the combination that ‘best explains’ the
patterns in the macrofaunal community composition. Analyses can also be performed that
identify the key environmental variables that best explain macrofaunal variance.
Hence the data can then be used to give an improved understanding of the current health of the
estuary, identify key anthropogenic stressors that effect biological communities and provide
baseline information for ongoing monitoring programmes. This information could then also be
used by iwi and researchers to prioritise research questions for further study.
Based on what is currently known, we outline below some possible case studies for future
research, focusing on shellfish and seagrass.
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5.3. Possible research on shellfish populations
Tauranga Harbour has extensive intertidal and shallow subtidal areas supporting a diverse
array of macroinvertebrates and shellfish beds. The harbour has been described as having
exceptionally high ecological value; it is productive and rich in species and habitat of
importance to the ecology of the greater region (Bioresearchers Ltd, 1976a; Bioresearchers
Ltd, 1976b) with large productive beds of shellfish throughout the harbour (Park and Donald,
1994).
Extensive shellfish beds (e.g. mussel, horse mussel, scallop) are important as they can add
complex physical structure to soft sediment habitats (Cummings et al., 2001) and provide
predation refuges (Woodin, 1978) and substrate for settlement of epifauna (Cummings et al.,
1998). Shellfish have been identified as particularly sensitive to suspended sediments (Norkko
et al., 2006) and the loss of key suspension feeding bivalves can occur in estuaries
experiencing high rates of sedimentation (Ellis et al., 2002), with the potential for larger-scale
functional and structural impacts on benthic and estuary ecosystems. Some shellfish beds have
been depleted by overharvesting (Bioresearchers 1976a).
Because of the cultural and ecological importance of shellfish, the sensitivity of these species
to suspended sediments, and the disappearance of shellfish beds seen in previous surveys, we
recommend shellfish as an area for further research. Determining current extent of shellfish
beds and identifying the factors that affect intertidal and subtidal species distribution are
primary research questions. A broad scale survey would provide current information on
species distribution within the harbour, size distribution and species habitat preferences as well
as information on physical variables including sedimentation, contamination and nutrients.
Ordination analyses and other techniques can then be used to link shellfish populations with
key anthropogenic stressors. Identification of the primary stressors on shellfish populations
provides necessary information to manage associated catchment activities.
Other topics could be investigated based on the broad scale survey data, supplemented by
further field experiments. These include:
1. The link between shellfish condition (measured by glycogen levels) and levels of
sedimentation and contaminants within the harbour.
2. The processes that influence population dynamics such as settlement processes and
larval recruitment and how these are effected by heavy metal contamination
(settlement occurs in the upper reaches of the estuary where contaminant loadings are
highest).
3. Whether existing levels of sedimentation or pollution limit the distribution of shellfish
beds (as determined from transplant experiments) in Tauranga Harbour.
4. How the loss of shellfish beds affects the ecological functioning of benthic
communities (e.g. nutrient fluxes, biodiversity, sediment stability).
5. Cumulative impacts and likely consequences of potential increases in sedimentation
due to climate change.
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5.4. Possible research on seagrass
The seagrass beds of Tauranga Harbour have been described as more extensive than in any
other New Zealand harbour (Barker and Larcombe, 1976) and were identified as one of nine
‘hotspots’ for seagrass distribution in New Zealand (MFish, 2006). Seagrass meadows provide
a number of ecosystem functions including enhancing primary production and nutrient cycling,
stabilizing sediment, protecting the coast from erosion and supporting high diversity plant and
animal communities e.g. by providing refuge from predators (Alfaro, 2006; Morrison et al.,
2007). Seagrass beds within the harbour have already declined substantially, including a 90%
decrease in subtidal areas. While sedimentation and nutrient loading have been implicated as
the main factors (Park, 1999a; Park, 1999b), determining the relative impacts of various
stressors on seagrass decline requires further research.
Due to the importance of seagrass habitats there are many outstanding research questions.
These include:
1. Identification of the factors driving seagrass decline, and whether these are the same in
subtidal and intertidal areas.
2. Assessing the role of seagrass beds in sustaining coastal fisheries.
3. Assessing how changes in subtidal and intertidal seagrass beds impact benthic
communities and biodiversity.
4. Determining whether fragmentation of these beds effects their functioning.
These questions highlight current gaps in our understanding of seagrass communities and
would benefit from further research. Identifying the factors that have the greatest effects on
seagrass is a high priority for research. Using data from the broad scale survey, ordination
analysis and species distribution modelling would provide insights into this question. It could
be further addressed by field experiments across a range of seagrass habitats that are exposed
to varying levels of nutrients and sediments. This should also include a selection of sites at
Tuapiro estuary where there is evidence of seagrass beds expanding.
In order to assess cumulative impacts on seagrass communities, other sources of human and
natural impacts besides sedimentation and nutrients need to be considered. Human impacts
include mechanical damage (e.g. dredging, fishing, anchor damage), introduced species, the
effects of coastal constructions and food web alterations, and negative effects of climate
change. Natural impacts include storm damage, disease, grazing by herbivores and natural
climatic variation. Further research on the stressors of seagrass, including sediment and
grazing by black swans, is currently being funded by BOPRC and results are expected in 2011.
As information becomes available from these studies, it can be used to develop models that
assess cumulative impacts on seagrass beds of small and large scale environmental changes.
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5.5. Possible research on mangrove ecosystems
In New Zealand mangroves are spreading in response to increased sediment loads into
estuaries and harbours. Within Tauranga Harbour, mangroves have expanded from 240 ha in
1943 to 623 ha in 2003 (S. Park, pers. comm.) with a high percentage of expansion occurring
in the last 20 to 40 years (Stokes et al., 2009). The rate of expansion has led some communities
to consider them to be a nuisance and BOPRC has approved coastal permits to allow removal
of mangroves in certain areas of Tauranga Harbour. However there are a number of
significant data gaps on both the ecological importance of mangrove habitats and the effects of
their removal. Specifically, outstanding research questions include:
1. What are the ecological consequences of the spread of mangroves into intertidal
sandflats?
2. What are the functional roles of mangroves in estuaries that are not heavily impacted
by sediments and how have these been modified by high rates of sediments and
nutrients?
3. How does the removal of mangroves impact intertidal mudflats and adjacent sandflats?
(Some work on this topic is currently being done by NIWA.)
4. What are the most effective catchment management initiatives to control sediment and
nutrient loadings into estuaries?
These are complex questions and possibly beyond what can be achieved in the present research
project, but it might be possible to investigate some of these questions in collaboration with
other researchers.
5.6. Summary
To summarize, the spatial scale over which information has been collected varies greatly from
one study to the next. Hence, while studies have been conducted on a wide range of topics,
information on biodiversity of flora and fauna does not exist at harbour scale. Studies that link
changes in biodiversity with varying stressors such as sediment, nutrients and pollutants have
not been conducted within Tauranga Harbour, although some inferences can be drawn from
research in other estuaries.
In order to generate a more comprehensive understanding of the role of varying anthropogenic
stressors on biodiversity in Tauranga Harbour, we recommend starting with a broad scale
survey and then using the resulting information to investigate the factors affecting populations
of key species such as seagrass, mangroves and shellfish. This information could then be used
by iwi and researchers to prioritise further research questions. Shellfish, seagrass beds and
mangrove habitats have been identified for further research due to their cultural and ecological
importance and due to documented impacts on these ecosystem components.
Manaaki Taha Moana Report No. 1
83
A number of other data gaps have also been identified. Sedimentation modeling has only been
carried out in the Southern Basin. Regarding contaminants, further research may be required
to develop strategies to reduce high levels of heavy metals in the upper estuary. This could
also include consideration of the development of an estuary monitoring protocol. Sea lettuce
blooms have become a significant source of concern, and identifying the primary factors
controlling blooms including sources of nutrients is an important research area. The Intercoast
research programme is currently conducting research on estuary-shelf nutrient exchange
effects on interannual patterns in sea lettuce dynamics and on the effects of decomposing algal
mats on benthic community structure and function. There is also limited information on the
importance of seaweeds as primary producers in the harbour and limited information specific
to phytoplankton including growth, mortality, dominance, succession or competition between
zooplankton and shellfish for phytoplankton.
Little is known about the diet of fish in Tauranga Harbour. This information would be needed
to understand the importance of specific habitats or species assemblages to higher tropic levels
and the importance of the harbour as a nursery habitat for fisheries. There is also currently
limited information to assess abundance estimates of dolphins and whales that use the harbour
and, therefore, the extent of top down predation on food webs.
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6.
ACKNOWLEDGEMENTS
Many people have assisted in the preparation of this report. In addition to those listed as
authors, Carlton Bidois and Tracey Ngatoko mentored and supported young research assistants
based at Waka Taiao, while Aaron McCallion, Kelley Solomon and their team at Waka Digital
provided an online data repository for keeping track of the many documents reviewed in
compiling the information now summarised in this report.
Rob Donald and Stephen Park of BOPRC responded to numerous requests for published
reports and data. The Port of Tauranga also provided reports.
We are especially grateful to Dr Chris Battershill of the University of Waikato, Lisette Collins
of Wildland Consultants, Kate Akers of NZ Landcare Trust, and Stephen Park of BOPRC,
each of whom reviewed a draft of this report and provided detailed comments. Thank you to
Keith Owen for providing comments on the bird section of the report.
The following generougly granted permission to use previously published material:
Waikato Regional Council and Wildland Consultants Ltd, the map of Tauranga
Harbour sub-catchments and LUC (Figure 2)
Roger Briggs, University of Waikato, the geological map of Tauranga and the
southern Kaimai Range (Figure 3)
Wildland Consultants Ltd, the map of land cover in the Tauranga District in 1840
and 2000 (Figure 5).
Noel Peterson provided a number of photographic images used in this report.
Funding for this report has been provided by the Ministry of Science and Innovation through
the Manaaki Taha Moana research programme led by Massey University.
Any remaining errors and omissions remain the responsibility of the authors.
Manaaki Taha Moana Report No. 1
85
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8.
APPENDICES
8.1. Appendix 1: Agencies with management functions relevant to
Tauranga Harbour
Three local authorities and several central government agencies have important management
functions and responsibilities that pertain to the health of Tauranga Harbour. Other agencies
and entities play supporting roles. All have a responsibility to work with tangata whenua to
protect Tauranga moana, an important taonga for local iwi and hapū.
8.1.1. Bay of Plenty Regional Council
Of the agencies with management responsibilities for Tauranga Harbour, the Bay of Plenty
Regional Council (BOPRC) has the most wide-ranging role in promoting sustainable
management. BOPRC has thirteen elected councillors of which three are elected from Māori
constituencies.
Under the Resource Management Act 1991 (RMA), BOPRC has the function of setting,
implementing and reviewing objectives, policies and methods to achieve integrated
management of the natural and physical resources of the region. Regional councils commonly
give effect to these responsibilities through their regional policy statements and regional plans,
as well as through plans and activities specified in their long term council community plans
and annual plans.
BOPRC’s role includes the specific functions of controlling land for the purpose of the
maintenance and enhancement of water quality and ecosystems in coastal waters and, within
the coastal marine area, controlling any actual or potential effects of land use or development
(see Box 1). BOPRC is also responsible for controlling all discharges to land, air and water
within the region, including from stormwater systems operated by city and district councils.
BOPRC’s regional policy statement became operative in 1999 and a new version is now being
prepared. The Proposed Regional Policy Statement 2010 was open for submissions until
February 2011. Once these are summarized and published, further submissions will be invited
and hearings held. Decisions on submissions are expected in late 2011 or early 20123. The
Regional Coastal Environmental Plan, approved in 2003, provides more detailed guidance on
the activities and effects that are allowed in Tauranga Harbour4. Some changes may follow the
release of a new National Coastal Policy Statement, which came into force on 3 December
2010. Other relevant regional plans include the Proposed Regional Water and Land Plan,
Regional Land Management Plan and the Onsite Effluent Treatment Regional Plan5.
3
http://www.boprc.govt.nz/knowledge-centre/policies/the-next-regional-policy-statement.aspx
http://www.boprc.govt.nz/knowledge-centre/plans/regional-coastal-environment-plan.aspx
5
Copies are available at http://www.boprc.govt.nz/knowledge-centre.aspx (accessed 30 June 2011).
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Box 1. RMA Functions of Bay of Plenty Regional Council
Under the Resource Management Act 1991 (section 30), Bay of Plenty Regional Council has
the following functions (emphasis added to highlight functions with particular relevance to
Tauranga Harbour):
(a) the establishment, implementation, and review of objectives, policies, and methods to
achieve integrated management of the natural and physical resources of the region:
(b) the preparation of objectives and policies in relation to any actual or potential effects of the
use, development, or protection of land which are of regional significance:
(c) the control of the use of land for the purpose of—
(i) soil conservation:
(ii) the maintenance and enhancement of the quality of water in water bodies and
coastal water:
(iii) the maintenance of the quantity of water in water bodies and coastal water:
(iiia) the maintenance and enhancement of ecosystems in water bodies and coastal
water:
(iv) the avoidance or mitigation of natural hazards:
(v) the prevention or mitigation of any adverse effects of the storage, use, disposal, or
transportation of hazardous substances:
(ca) the investigation of land for the purposes of identifying and monitoring contaminated
land:
(d) in respect of any coastal marine area in the region, the control (in conjunction with the
Minister of Conservation) of—
(i) land and associated natural and physical resources:
(ii) the occupation of space on land of the Crown or land vested in the regional council,
that is foreshore or seabed, and the extraction of sand, shingle, shell, or other natural material
from that land:
(iii) the taking, use, damming, and diversion of water:
(iv) discharges of contaminants into or onto land, air, or water and discharges of water
into water:
(iva) the dumping and incineration of waste or other matter and the dumping of ships,
aircraft, and offshore installations:
(v) any actual or potential effects of the use, development, or protection of land,
including the avoidance or mitigation of natural hazards and the prevention or mitigation of
any adverse effects of the storage, use, disposal, or transportation of hazardous substances:
(vi) the emission of noise and the mitigation of the effects of noise:
(vii) activities in relation to the surface of water:
(e) the control of the taking, use, damming, and diversion of water, and the control of the
quantity, level, and flow of water in any water body, including—
(i) the setting of any maximum or minimum levels or flows of water:
(ii) the control of the range, or rate of change, of levels or flows of water:
(iii) the control of the taking or use of geothermal energy:
(f) the control of discharges of contaminants into or onto land, air, or water and
discharges of water into water:
(fa) if appropriate, the establishment of rules in a regional plan to allocate any of the
following:
(i) the taking or use of water (other than open coastal water):
(ii) the taking or use of heat or energy from water (other than open coastal water):
(iii) the taking or use of heat or energy from the material surrounding geothermal
water:
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(iv) the capacity of air or water to assimilate a discharge of a contaminant:
(fb) if appropriate, and in conjunction with the Minister of Conservation,—
(i) the establishment of rules in a regional coastal plan to allocate the taking or use of
heat or energy from open coastal water:
(ii) the establishment of a rule in a regional coastal plan to allocate space in a coastal
marine area under Part 7A:
(g) in relation to any bed of a water body, the control of the introduction or planting of any
plant in, on, or under that land, for the purpose of—
(i) soil conservation:
(ii) the maintenance and enhancement of the quality of water in that water body:
(iii) the maintenance of the quantity of water in that water body:
(iv) the avoidance or mitigation of natural hazards:
(ga) the establishment, implementation, and review of objectives, policies, and methods for
maintaining indigenous biological diversity:
Regional councils also have functions related to monitoring and reporting on the state of the
environment, and typically issue “state of the environment” reports, sometimes providing a
general overview of the entire region, other times focussing on particular resources. BOPRC
has taken the latter approach.
Finally, BOPRC has additional functions under other legislation, e.g. for regional transport and
civil emergencies, as well as the Local Government Act. Some aspects of resource
management, e.g. flood control, are still carried out under the Soil Conservation and Rivers
Control Act of 1941. BOPRC also administers some regional functions for Maritime New
Zealand (see below).
The regional council has a Tauranga Harbour Integrated Management Strategy (Environment
Bay of Plenty, 2006) that identifies sedimentation of Tauranga Harbour as the largest
environmental management issue for the western part of the Bay of Plenty. BOPRC
subsequently commissioned research by NIWA to identify the sources of this sediment, by
catchment. The results of that study are presented in section 3.2 of this report.
8.1.2. Territorial Authorities
As territorial authorities, Tauranga City Council and Western Bay of Plenty District Council
have different statutory functions than BOPRC. In particular, they provide key infrastructure
services to residents, including water supply, sewerage and stormwater systems, as well as
local roads and reserves. Under the RMA 1991, territorial authorities are responsible for
“integrated management of the effects of the use, development, or protection of land and
associated natural and physical resources of the district”. Box 2 provides more detail on the
RMA functions of territorial authorities.
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Box 2. RMA Functions of territorial authorities (section 31)
(1) Every territorial authority shall have the following functions for the purpose of giving
effect to this Act in its district:
(a) the establishment, implementation, and review of objectives, policies, and methods
to achieve integrated management of the effects of the use, development, or protection of land
and associated natural and physical resources of the district:
(b) the control of any actual or potential effects of the use, development, or protection
of land, including for the purpose of—
(i) the avoidance or mitigation of natural hazards; and
(ii) the prevention or mitigation of any adverse effects of the storage, use, disposal,
or transportation of hazardous substances; and
(iia) the prevention or mitigation of any adverse effects of the development,
subdivision, or use of contaminated land:
(iii) the maintenance of indigenous biological diversity:
(c) [Repealed]
(d) the control of the emission of noise and the mitigation of the effects of noise:
(e) the control of any actual or potential effects of activities in relation to the surface of
water in rivers and lakes:
(f) any other functions specified in this Act.
(2) The methods used to carry out any functions under subsection (1) may include the
control of subdivision.
Territorial authorities give effect to these functions via their district plans. These plans provide
detailed guidance on land use within the district, including which areas may be used for which
purpose.
8.1.3. Department of Conservation
Under the RMA 1991, the Minister of Conservation has specific functions in relation to the
coastal marine area. In particular, the Minister is responsible for the New Zealand Coastal
Policy Statement, a new version of which came into effect on 3 December 2010, and the
approval of regional coastal plans prepared by regional councils. The Minister therefore
provides the overarching policy and guidance for the sustainable management of New
Zealand’s coastal environment. Until a legislative amendment in 2009, the Minister also had
the responsibility of deciding applications for coastal permits for activities classified as
“restricted coastal activities” under the RMA 1991.
Under the provisions of the Conservation Act 1987 and the Wildlife Act 1953, the Department
of Conservation (DOC) has responsibilities related to the protection of seabirds and marine
mammals, and also manages whitebait fishing.
Within the catchments of Tauranga Harbour, DOC also manages large areas of land, including
the Kaimai-Mamaku Forest Park. Within such areas, DOC is responsible for protecting native
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biodiversity, pest control, concessions, recreation, historic sites, and fire control, among other
duties.
DOC also works with other agencies and local authorities to promote sustainable management
of natural resources beyond the conservation estate, in support of its mission to maintain and
enhance New Zealand’s native biodiversity.
8.1.4. Ministry of Fisheries
The Ministry of Fisheries (MFish) is responsible for managing customary, commercial and
recreational fisheries to provide for sustainable utilisation under the Fisheries Act 1996.
MFish’s main functions under this Act are to set and monitor total allowable catches for
fisheries, recreational bag limits, and fishing gear regulations, and to otherwise manage fishing
activity. MFish seeks to ensure that fish stocks do not fall below the levels that will produce
maximum sustainable yield, and to protect associated and dependent species.
MFish is responsible for management of all marine fishing and for eel fishing in freshwater
environments. As noted above, DOC manages whitebait, while Fish and Game New Zealand
manages introduced trout and salmon.
The Ministry of Fisheries will merge with the Ministry of Agriculture and Forestry on 1 July
2011, although the two bodies will retain their separate identities until a date yet to be
announced.
The Tauranga Moana Customary Fisheries Committee advises the Minister of Fisheries on
how best to manage fishing within the local mataitai around Mount Maunganui – see section
4.2.2 of this report.
8.1.5. MAF Biosecurity New Zealand
MAF Biosecurity New Zealand (MAFBNZ) is the division of the Ministry of Agriculture and
Forestry (MAF) charged with leadership of New Zealand’s biosecurity system, i.e. which
seeks to prevent the introduction of non-native species from overseas and manage those that
are already established.
MAFBNZ has lead responsibility for border control (e.g. managing discharge of ballast water
and arriving vessels with hull fouling), surveillance, and response to new incursions.
MAFBNZ works with regional councils and other bodies on pest management for unwanted
species that are well established and for which eradication is not deemed to be a viable option.
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8.1.6. Maritime New Zealand
The mission of Maritime New Zealand (formerly the Maritime Safety Authority) is to lead and
support the maritime community to take responsibility for ensuring New Zealand seas are safe,
secure and clean.
Maritime New Zealand has overall responsibility for managing discharges of waste from
vessels and for reducing the risk of accidental spills of harmful substances such as oil or
chemicals, as well as responding to spills that do occur. BOPRC carries out many of these
functions at a regional level.
All vessels (including recreational), gas and oil installations, and ports operating in New
Zealand waters must comply with a range of environmental regulations, including rules,
conventions and legislation, administered by Maritime New Zealand.
8.1.7. Ministry for the Environment
The Ministry for the Environment (MfE) is the lead agency for implementation of the RMA
1991. In addition to monitoring the performance of regional and territorial authorities under
the Act, MfE and its Minister have responsibility for national policy statements and
environmental standards (except for the NZ Coastal Policy Statement, which is the
responsibility of the Minister of Conservation). Policies and plans developed by local
authorities under the RMA must be consistent with and give effect to national policy
statements.
A National Policy Statement (NPS) on Freshwater Management has been under development
for several years. Following a Board of Inquiry report with recommendations in January 2010
and recommendations from the Land and Water Forum in September 2010, the Minister for the
Environment released a final NPS on Freshwater Management in May 2011. Of relevance to
Tauranga Harbour, the NPS requires that regional councils make or change regional plans to
set freshwater objectives and water quality limits, and to provide for the integrated
management of the effects of land use and development, including on the coastal environment.
Councils are to implement the NPS “as promptly as is reasonable in the circumstances”. Where
a council is satisfied this cannot be achieved by the end of 2014, it may do this in stages so that
it is completed by 2030.
MfE has several national environmental standards in development at present, including on the
following topics6:
6
ecological flows and water levels in freshwater systems
contaminants in soil
See http://www.mfe.govt.nz/laws/standards/index.html for more information.
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future sea level rise
on-site wastewater systems (e.g. septic tanks)
plantation forestry.
Each of these has potential implications for the health of Tauranga Harbour. Because of the
influence of sediment and other contaminants that enter the coastal environment via rivers and
streams, the NPS and the national standards on ecological flows and on plantation forestry
could have a particularly significant effect on the objectives and policies adopted by local
authorities and hence whether the health of the harbour improves or continues to decline.
8.1.8. Fish and Game New Zealand
Fish and Game New Zealand is made up of twelve Regional Fish & Game Councils and one
National Council. The National Council coordinates regional activities and speaks for anglers
and hunters on issues of national importance. Fish and Game Councils were established under
the Conservation Act 1987 as amended by the Conservation Law Reform Act 1990. They
have a statutory function to “manage, maintain, and enhance the sports fish and game bird
resource in the recreational interests of anglers and hunters” (Section 26P of the Conservation
Act). Fish and Game’s management of waterfowl is of particular relevance to Tauranga
Harbour; key species of interest are grey and mallard duck, shoveler duck, paradise shelduck,
pukeko, Canada geese and black swan.
In their role as statutory managers of sports fish and game birds, Fish and Game councils set
and monitor bag limits and license fees as well as other regulations. Like DOC, Fish and
Game also has an advocacy role, working with central and local government agencies and with
other stakeholders to promote the sustainable management of land and water resources that
provide or affect habitat for game fish and birds.
Tauranga Harbour is within the Eastern Region of Fish and Game New Zealand, which has its
headquarters in Rotorua.
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8.2. Appendix 2: Community composition of submerged reef biota off
Motuotau Island
The following table details a presence-absence record of species observed at the three
Motuotau Island reef sites monitored from 1990-2009 (Ross and Pilditch, 2009). ‘X’ indicates
the species was present at the site. This species list is in no way exhaustive and should not be
interpreted as such.
Group
Common Name
Species Name
Algae
Brown algae
Brown algae
Brown algae
Carpomitra sp.
Carpophyllum flexuosum
Carpophyllum
maschalocarpum
Cystophora
Lessonia variegata
Zonaria angustata
Sargassum sp.
Corallinales order
Corallinales order
Ecklonia radiata
Ptericladia lucida
Rhodymenia sp.
Ulva sp.
Cliona celata
Iophon minor
Polymastia fusca
Sponges
Molluscs
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Brown algae
Brown algae
Brown algae
Brown algae
Coralline paint
Coralline turf
Kelp
Red algae
Red algae
Sea lettuce
Boring sponge
Branching sponge
Brown football
Crumbly cream
Delicate mauve
Finger sponge
Golfball sponge
Golfball sponge
Massive grey
Orange football
Orange branching
Pale grey encrusting
Purple encrusting
Purple/grey sphere
Small pink sponge
Tennis ball sponge
Yellow fine finger
Beaded top shell
Blue/brown nudibranch
Brown nudibranch
Butterfly chiton
Clown nudibranch
Cook’s turban
Calyspongia ramosa
Tethya aurantium
Tethya ingalli
Ancorina alata
Polymastia granulosa
Raspailia sp.
Control
Site
Site
2
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Aaptos aaptos
Calliostoma punctulatum
Nudibranchia
Nudibranchia
Cryptoconchus porosus
Ceratosoma amoena
Cookia sulcata
Site
1
X
X
X
X
X
X
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Group
Echinoderms
Crustaceans
Annelida
Ascidians
Coelenterates
Common Name
Species Name
Gem nudibranch
Green mussel
Lined whelk
Maori octopus
Noble chiton
Nudibranch
Nudibranch eggs
Smooth light nudibranch
Spengler’s trumpet
Squid eggs
Tiger shell
White rock shell
Brittle star
Kina
Reef star
Sea cucumber
Barnacles
Crayfish
Hermit crab
Pink barnacle
Red rock crab
Tube worm
Web building terebellid
Blue sea squirt
Brown sea squirt
Large simple ascidian
Orange golfball
Purple encrusting
compound ascidian
Purple mushroom
Sea tulip
Small red simple
Dendrodoris deisoni
Perna canaliculus
Buccinulum lineum
Octopus maoruam
Eudoxochiton nobilis
Glossodoris atromarginata
Nudibranchia
Aphlelodoris luctuosa
Cabestana spengleri
Teuthida order
Calliostoma tigris
Thais orbita
Pectinura maculata
Evechinus chloroticus
Stichaster australis
Stichopus mollis
Cirrpedia
Jasus edwardsii
Pagurus novizealandiae
Balanus decorus
Guinusia chabrus
Chaetopterous sp.
Dead man’s fingers
White-striped anemone
Cup coral
Hydroids
White zoanthid
Jewel anemone
Mussel beard
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Control
Site
X
Site
1
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Hiptistoza sp.
Pyura pachydermatina
Didemnum sp.
Sigillinaria arenosa
Alcyonium aurantium
Actinothoe albocincta
Flabellum rubrum
Corynactis hoddoni
Sertularia sp.
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Cnemidocarpa sp.
Site
2
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
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8.3. Appendix 3: Birds of Tauranga Harbour
The following table lists birds that have been recorded as present in or around Tauranga Harbour (Beadel et al., 2003b; Eastern
Region Fish and Game Council, 2010; Ellis et al., 2008; Greenway et al., 2006; Heather and Robertson, 2005; Owen, 1993).
Endemic birds occur only in New Zealand and are protected by the Wildlife Act.
Native birds occur naturally in New Zealand, whether through self-introduction or migration. Those listed here also occur
overseas, and include migratory shorebirds. Most are fully protected under the Wildlife Act.
Migrant brids are regular visitors but do not breed in New Zealand.
Introduced birds are either deliberately released cage birds or birds brought over with the early settlers from Europe and Asia.
They are not protected but some are managed by Fish and Game New Zealand (see Appendix 1).
Conservation status is based on the New Zealand Threat Classification System (Miskelly et al., 2008).
Common Name
Endemic birds
Banded dotterel
Banded rail*
Bellbird
Black-billed gull
Black stilt
Marsh crake*
North Island fernbird
Northern New Zealand dotterel
New Zealand dabchick
New Zealand kingfisher*
New Zealand pigeon
New Zealand scaup
New Zealand shoveler
Paradise shelduck
Red-billed gull*
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Scientific Name
Māori Name
Conservation status
Charadrius bibinctus bicinctus
Rallus philippensis assimilis
Anthornis melanura melanura
Larus bulleri
Himantopus novaezelandiae
Porzana pusilla affinis
Bowdleria punctata vealeae
Charadrius obscurus aquilonius
Poliocephalus rufopectus
Todiramphus sanctus vagans
Hemiphaga novaeseelandiae
Aythya novaeseelandiae
Anas rhynchotis variegata
Tadorna variegata
Larus novaehollandiae scopulinus
Tuturiwhata
Moho-perehu
Korimako
Tarapunga
Kaki
Kāreke
Matata
Tuturiwhatu
Weweia
Kotare
Kereru
Papango
Kuruwhengi
Putangitangi
Tarapunga
Nationally vulnerable
Naturally uncommon
Not threatened
Nationally endangered
Nationally Critical
Relict
Declining
Nationally vulnerable
Nationally vulnerable
Not threatened
Not threatened
Not threatened
Not threatened
Not threatened
Nationally vulnerable
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Common Name
Endemic birds (cont.)
South Island pied oystercatcher*
Southern black-backed gull*
Tui
Variable oystercatcher
Wrybrill
Native birds
Australasian bittern
Australasian gannet
Australasian harrier
Black shag
Blue penguin
Caspian tern
Fantail
Grey duck
Grey teal
Grey warbler
Grey-faced petrel
Little black shag
Little shag
Morepork
Pied shag
Pied stilt
Pukeko
Reef heron
Royal spoonbill
Shining cuckoo
Silvereye
Spotless crake
Spur-winged plover
Sooty shearwater
Welcome swallow
White heron
White-faced heron
White-fronted tern
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Scientific Name
Māori Name
Conservation status
Haematopus ostralegus finschi
Larus dominicanus domincanus
Prosthemadera novaeseelandiae novaeseelandiae
Haematopus unicolor
Anarhynchus frontalis
Torea
Karoro
Tui
Torea pango
Ngutuparore
Declining
Not threatened
Not threatened
Recovering
Nationally vulnerable
Botaurus poiciloptilus
Morus serrator
Circus approximans
Phalacrocorax carbo novaehollandiae
Eudyptula minor
Hydroprogne caspia
Rhipidura fuliginosa
Anas superciliosa superciliosa
Anas gracilis
Gerygone igata
Pterodoma macroptera gouldi
Phalacrocorax sulcirostris
Phalacrocorax melanoleucos
Ninox novaeseelandiae novaeseelandiae
Phalacrocorax varius varius
Himantopus himantopus leucocephalus
Porphyrio melanotus
Egretta sacra sacra
Platalea regia
Chrysococcyx lucidus lucidus
Zosterops lateralis lateralis
Porzana tabuensis plumbea
Vanellus miles novaehollandiae
Puffinus griseus
Hirundo tahitica neoxena
Adrea modesta
Ardea novaehollandiae
Sterna striata striata
Matuku
Takapu
Kahu
Kawau
Korora
Taranui
Piwakawaka
Parera
Tete
Riroriro
Oi
Kawaupaka
Kawaupaka
Ruru
Karuhiruhi
Poaka
Pukeko
Matuku moana
Kotuku ngutupapa
Pipiwharauroa
Tauhou
Puweto
Nationally endangered
Not threatened
Not threatened
Naturally uncommon
Declining
Nationally vulnerable
Not threatened
Nationally Critical
Not threatened
Not threatened
Not threatened
Naturally uncommon
Naturally uncommon
Not threatened
Nationally vulnerable
Declining
Not threatened
Nationally vulnerable
Naturally uncommon
Not threatened
Not threatened
Relict
Not threatened
Declining
Not threatened
Nationally critical
Not threatened
Declining
Titi
Warou
Kotuku
Matuku
Tara
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Common Name
Migrant birds
Asiatic black-tailed godwit
Knot
Eastern bar-tailed godwit
Far-eastern curlew
Hudsonian godwit
Pacific golden plover
Turnstone
Whimbrel sp.
Introduced birds
Australian magpie
Black swan
California quail
Canada goose
Chaffinch
Common myna
Common pheasant
Eurasian blackbird
European goldfinch
Greylag goose
House sparrow
Mallard
Rock pigeon
Song thrush
Starling
*Endemic at sub-species level
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Scientific Name
Limosa limosa melanuroides
Calidris canutus rogersi
Limosa lapponica baueri
Numenius madagascariensis
Limosa haemastica
Pluvialis fulva
Arenaria interpres
Numenius sp.
Māori Name
Huahou
Kuaka
Conservation status
Vagrant
Migrant
Migrant
Migrant
Vagrant
Migrant
Migrant
Migrant/Vagrant
Gymnorhina tibicen
Cygnus atratus
Callipepla californica
Branta canadensis
Fringilla coelebs
Acridotheres tristis
Phasianus colchicus
Turdus merula
Carduelis carduelis
Anser anser
Passer domesticus
Anas platyrhynchos
Columba livia
Turdus philomelos
Sturnus vulgaris
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