- Coastal and Marine Research Institute, Nelson Mandela Metropolitan University, Port Elizabeth.
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- Marine Ecology, Conservation, Remote sensing and GIS, Marine Protected Areas, Foraging ecology, Pelagic Ecosystems and Small Pelagic Fishes, and 16 moreCape gannets, Predator-Fisheries Interaction, African penguins, Bio-Logging, Seabird Life History Traits, Zoology, Ecology, Conservation Biology, Seabirds, Ecosystem-based Fishery Management, Conservation Biology and Ecology of Seabirds and Islands, Penguins, Climate Change, Ecosystem Approach to fisheries managemetn, Group Foraging, and Biologyedit
- My research focuses on seabirds foraging ecology and life history traits in relation with prey availability and local... moreMy research focuses on seabirds foraging ecology and life history traits in relation with prey availability and local competition with industrial fisheries. I use animal-borne miniaturized recorders, such as GPS recorders combined with pressure sensors, cameras, etc, taped on adults breeding small chicks to determine the at-sea behaviour of several species of seabirds breeding in South Africa, all endemic to the region and threatened with extinction: the Cape gannet, the African penguin and the Cape cormorants. All three species have similar diet, small pelagic fish such as sardines and anchovies, yet different foraging and breeding strategies.
Through a decade of monitoring Cape gannets’ foraging behaviour and breeding success on the colony of Malgas Island, off the West Coast of South Africa, with the help of students and collaborators, we discovered the flexibility of these predators. Able to increase their energy and time spent at sea in search of their favourite prey, they will eventually turn to feed on the easy target of fishery discards if small pelagic fish are too scarce. Such diet apparently increased their winter survival and did not seem to have a long term effect on the body condition of adults, even after several years of feeding consistently on such a diet. However, their chicks have hardly a chance to fledge on this poor-energy food, constituted of fish bones, heads and guts. Therefore, we refuted the argument that providing discards for seabirds could compensate for the removal of their natural prey and highlighted the potential for high competition between seabirds and purse-seine fishing in the Benguela, to the detriment of the birds.
As part of a national experiment to determine if the drastic recent decreases in African penguin numbers, now Endangered, could be reduced by excluding fishing from penguin foraging areas, extensive monitoring take place on some African penguin colonies, some closed to fishing and some open, since 2008. Being a member of the Island Closure Task Team, part of the Small Pelagic Working Group from the Department of Agriculture, Forests and Fisheries, I’m in charge of monitoring the set of two islands in Algoa Bay, off Port Elizabeth. With the extensive help of many students and colleagues, as well as rangers from South African National Parks, we monitor their breeding success, chick growth, foraging behaviour, diet, survival and since recently, the distribution and abundance of their prey over time, in relation with purse-seine fishing activities. Shortly after fishing exclusion, breeding African penguins reduced their energy spent at sea in search for food, probably increasing their survival. However, the size of the fishing exclusion zone still remains insufficient to reverse the penguin population trends, with penguin chick growth and their breeding success remaining very low. While suggesting increasing the size of the fishing exclusion zone as a precautionary approach to prevent further loss in penguin numbers, we’re now concentrating on understanding penguin-prey interaction in relation with ocean-physical processes, in the hope to help in refining conservation strategies and optimize the use of the marine resources by fisheries and marine predators.edit
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SummaryStorms can cause widespread seabird strandings and wrecking1,2,3,4,5, yet little is known about the maximum wind speeds that birds are able to tolerate or the conditions they avoid. We analyzed > 300,000 hours of tracking data... more
SummaryStorms can cause widespread seabird strandings and wrecking1,2,3,4,5, yet little is known about the maximum wind speeds that birds are able to tolerate or the conditions they avoid. We analyzed > 300,000 hours of tracking data from 18 seabird species, including flapping and soaring fliers, to assess how flight morphology affects wind selectivity, both at fine scales (hourly movement steps) and across the breeding season. We found no general preference or avoidance of particular wind speeds within foraging tracks. This suggests seabird flight morphology is adapted to a “wind niche”, with higher wing loading being selected for in windier environments. In support of this, wing loading was positively related to the median wind speeds on the breeding grounds, as well as the maximum wind speeds in which birds flew. Yet globally, the highest wind speeds occur in the tropics (in association with tropical cyclones) where birds are morphologically adapted to low median wind speeds. ...
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Fear effects of predators on prey distributions are seldom considered in marine environments, especially over large spatial scales and in conservation contexts. To fill these major gaps, we tested the Seascape of Fear Hypothesis in the... more
Fear effects of predators on prey distributions are seldom considered in marine environments, especially over large spatial scales and in conservation contexts. To fill these major gaps, we tested the Seascape of Fear Hypothesis in the Benguela marine ecosystem off South Africa. Using electronic tracking data, we showed that Cape gannets and their predator, the Cape fur seal, co-occurred in daytime and competed with fisheries within coastal areas. At night, gannets are particularly vulnerable to seals, and 28% of the birds returned to the safety of their breeding colony. The remaining 72% slept at the sea surface, but shifted to offshore areas with lower seal attendance, reducing predation risk by 25%. Overall, our integrative study demonstrates how fear and competition shape the seascape of threatened Cape gannets within a marine environment perturbed by climate change and overfishing. Such knowledge has strong implications for the design of marine protected areas.
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Norwegian Northern Gannet Morus bassanus populations exhibit contrasted trends at a regional scale and several colony extinctions occurred in recent decades. In an attempt to understand the ecological drivers of such variability, we... more
Norwegian Northern Gannet Morus bassanus populations exhibit contrasted trends at a regional scale and several colony extinctions occurred in recent decades. In an attempt to understand the ecological drivers of such variability, we tested whether resource availability is a factor limiting the current development of gannetries in the Lofoten/Vesterålen area. Between 2007 and 2010, we recorded arrival and departure times of breeding gannets from two colonies from regions showing contrasting population growth rates during the past two decades. We also recorded the duration of joint attendances by gannet parents at the nest, performed opportunistic diet sampling and counted numbers of occupied nests. Finally, we compiled ring recoveries over a 30-year period to assess inter-colony movements. Norwegian gannet parents spent more time together, attending their chick, and performed shorter foraging trips than those in British and French colonies of similar size. This suggests that, despite...
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Research Interests: Conservation Biology, Marine Protected Areas, Biology, Seabirds, Endangered Species, and 12 moreEcosystem-based Fishery Management, Biological Sciences, Foraging, Environmental Sciences, Population, Biological Conservation, Fishing, Biological, Fishery, Marine Protected Area, Marine Reserve, and pelagic zone
Marine piscivores have evolved a variety of morphological and behavioural adaptations, including group foraging, to optimize foraging efficiency when targeting shoaling fish. For penguins that are known to associate at sea and feed on... more
Marine piscivores have evolved a variety of morphological and behavioural adaptations, including group foraging, to optimize foraging efficiency when targeting shoaling fish. For penguins that are known to associate at sea and feed on these prey resources, there is nonetheless a lack of empirical evidence to support improved foraging efficiency when foraging with conspecifics. We examined the hunting strategies and foraging performance of breeding African penguins equipped with animal-borne video recorders. Individuals pursued both solitary as well as schooling pelagic fish, and demonstrated independent as well as group foraging behaviour. The most profitable foraging involved herding of fish schools upwards during the ascent phase of a dive where most catches constituted depolarized fish. Catch-per-unit-effort was significantly improved when targeting fish schools as opposed to single fish, especially when foraging in groups. In contrast to more generalist penguin species, African penguins appear to have evolved specialist hunting strategies closely linked to their primary reliance on schooling pelagic fish. The specialist nature of the observed hunting strategies further limits the survival potential of this species if Allee effects reduce group size-related foraging efficiency. This is likely to be exacerbated by diminishing fish stocks due to resource competition and environmental change
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Abstract Fisheries are often accused of starving vulnerable seabirds, yet evidence for this claim is scarce. Foraging energetics may provide efficient, short-term indicators of the fitness status of seabirds competing with fisheries. We... more
Abstract Fisheries are often accused of starving vulnerable seabirds, yet evidence for this claim is scarce. Foraging energetics may provide efficient, short-term indicators of the fitness status of seabirds competing with fisheries. We used this approach in Cape gannets (Morus capensis) from Malgas Island, South Africa, which feed primarily on small pelagic fish in the southern Benguela upwelling region, thereby competing with purse-seine fisheries. During their 2011–2014 breeding seasons, we determined body condition of breeding adult Cape gannets and measured their chick growth rates. In addition to these conventional fitness indices, we assessed the daily energy expenditure of breeding adults using a high-resolution time-energy budget derived from GPS-tracking and accelerometry data. For these same individuals, we also determined prey intake rates using stomach temperature recordings. We found that adult body condition and chick growth rates declined significantly during the study period. Crucially, most birds (73 %) studied with electronic recorders spent more energy than they gained through foraging, and 80–95 % of their feeding dives were unsuccessful. Our results therefore point to unprofitable foraging in Cape gannets, with a longer-term fitness cost in terms of adult body condition and reproductive performance that corresponds to a local population decline. Based on this evidence, we advocate a revision of regional fishing quotas for small pelagic fish and discuss the possibility of an experimental cessation of purse-seine fishing activities off the west coast of South Africa. These measures are needed for the ecological and socio-economical persistence of the broader southern Benguela upwelling ecosystem.
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This account presents the first known observations of Cape Gannet Morus capensis fledgling mortalities as a result of aggressive nest defence behaviour by African Penguins Spheniscus demersus. Observations were conducted in 2013 on Bird... more
This account presents the first known observations of Cape Gannet Morus capensis fledgling mortalities as a result of aggressive nest defence behaviour by African Penguins Spheniscus demersus. Observations were conducted in 2013 on Bird Island, Algoa Bay, South Africa – the world’s largest breeding colony of Cape Gannets. Twentyeight attacks were witnessed between 21 March and 18 May 2013 of which 16 resulted in mortality. The absence of previous observations of this phenomenon may be due to an unusually high proportion of African Penguin chicks being present relatively early on in the breeding season, associated with a potential for increased nest defence at this stage, and a larger number of gannet fledglings that year compared to previous years over the same period.Keywords: interspecific aggression, nest defence behaviour, seabirdsOSTRICH 2014, 85(2): 193–19
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The population of the Endangered African penguin Spheniscus demersus has decreased by > 65% in the last 20 years. A major driver of this decrease has been the reduced availability of their principal prey, sardine Sardinops sagax and... more
The population of the Endangered African penguin Spheniscus demersus has decreased by > 65% in the last 20 years. A major driver of this decrease has been the reduced availability of their principal prey, sardine Sardinops sagax and anchovy Engraulis encrasicolus. To date, conservation efforts to improve prey availability have focused on spatial management strategies to reduce resource competition with purse-seine fisheries during the breeding season. However, penguins also undergo an annual catastrophic moult when they are unable to feed for several weeks. Before moulting they must accumulate sufficient energy stores to survive this critical life-history stage. Using GPS tracking data collected between 2012 and 2019, we identify important foraging areas for pre- and post-moult African penguins at three of their major colonies in South Africa: Dassen Island and Stony Point (Western Cape) and Bird Island (Eastern Cape). The foraging ranges of pre- and post-moult adult African peng...
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Animal-borne-video footage showing the foraging behaviour of African penguins including an elevated school event, targeting of depolarised fish, group foraging and a bait-ball event.
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The African Penguin Spheniscus demersus is an endangered seabird endemic to southern Africa, and killing sprees by terrestrial predators have been one of the main threats for its mainland colonies. The methods employed to manage predators... more
The African Penguin Spheniscus demersus is an endangered seabird endemic to southern Africa, and killing sprees by terrestrial predators have been one of the main threats for its mainland colonies. The methods employed to manage predators may differ depending on the species involved, therefore the implementation of strategies to limit the impacts of predation relies on the correct identification of the culprit predator. We report and quantify the lesions seen in African Penguins killed by four species of terrestrial predators: Caracal Caracal caracal (52 kills), Leopard Panthera pardus (27 kills), Domestic Dog Canis lupus familiaris (10 kills), and Cape Grey Mongoose Galerella pulverulenta (4 kills). We discuss patterns of necropsy findings that can be used to identify the predator species involved. Traditional forensic methods are useful tools to direct species-specific management actions for the conservation of the African Penguin and other seabirds so that effective mitigating me...
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Global forage-fish landings are increasing, with potentially grave consequences for marine ecosystems. Predators of forage fish may be influenced by this harvest, but the nature of these effects is contentious. Experimental fishery... more
Global forage-fish landings are increasing, with potentially grave consequences for marine ecosystems. Predators of forage fish may be influenced by this harvest, but the nature of these effects is contentious. Experimental fishery manipulations offer the best solution to quantify population-level impacts, but are rare. We used Bayesian inference to examine changes in chick survival, body condition and population growth rate of endangered African penguinsin response to 8 years of alternating time-area closures around two pairs of colonies. Our results demonstrate that fishing closures improved chick survival and condition, after controlling for changing prey availability. However, this effect was inconsistent across sites and years, highlighting the difficultly of assessing management interventions in marine ecosystems. Nevertheless, modelled increases in population growth rates exceeded 1% at one colony; i.e. the threshold considered biologically meaningful by fisheries management ...
Research Interests: Geography, Marine Protected Areas, Fisheries Management, Seabirds, Medicine, and 13 moreBiological Sciences, Population, Fishing, Predation, Ecosystem based management, Fishery, Predator, African penguins, Marine ecosystem, African Penguin, Forage Fish, Fishing closures, and Medical and Health Sciences
Marine piscivores have evolved a variety of morphological and behavioural adaptations, including group foraging, to optimize foraging efficiency when targeting shoaling fish. For penguins that are known to associate at sea and feed on... more
Marine piscivores have evolved a variety of morphological and behavioural adaptations, including group foraging, to optimize foraging efficiency when targeting shoaling fish. For penguins that are known to associate at sea and feed on these prey resources, there is nonetheless a lack of empirical evidence to support improved foraging efficiency when foraging with conspecifics. We examined the hunting strategies and foraging performance of breeding African penguins equipped with animal-borne video recorders. Individuals pursued both solitary as well as schooling pelagic fish, and demonstrated independent as well as group foraging behaviour. The most profitable foraging involved herding of fish schools upwards during the ascent phase of a dive where most catches constituted depolarized fish. Catch-per-unit-effort was significantly improved when targeting fish schools as opposed to single fish, especially when foraging in groups. In contrast to more generalist penguin species, African ...
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Summary Climate change and fishing impact marine ecosystems, potentially modifying the availability of small pelagic fish to marine top predators. Some seabirds that primarily rely upon these resources have switched to feeding on fishery... more
Summary Climate change and fishing impact marine ecosystems, potentially modifying the availability of small pelagic fish to marine top predators. Some seabirds that primarily rely upon these resources have switched to feeding on fishery waste. It has therefore been argued that seabirds might become dependent upon this artificial resource. To test this hypothesis, we studied the foraging behaviour of Cape gannets Morus capensis breeding off the coast of South Africa using high‐resolution Global Positioning System‐tracking in relation to the availability of pelagic fish assessed by acoustic at‐sea surveys, and fishing effort by the two main south African fisheries (purse seiners that compete with seabirds for pelagic fish, and demersal trawlers that process fish at sea and discharge fish waste) tracked with vessel monitoring systems. Conjoint seabird, fish and fisheries information were analysed at mesoscale (c. 100 km) and sub‐mesoscale (c. 10 km) in years of high (2002), medium (20...
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Seismic surveys in search for oil or gas under the seabed, produce the most intense man-made ocean noise with known impacts on invertebrates, fish and marine mammals. No evidence to date exists, however, about potential impacts on... more
Seismic surveys in search for oil or gas under the seabed, produce the most intense man-made ocean noise with known impacts on invertebrates, fish and marine mammals. No evidence to date exists, however, about potential impacts on seabirds. Penguins may be expected to be particularly affected by loud underwater sounds, due to their largely aquatic existence. This study investigated the behavioural response of breeding endangered African Penguins Spheniscus demersus to seismic surveys within 100 km of their colony in South Africa, using a multi-year GPS tracking dataset. Penguins showed a strong avoidance of their preferred foraging areas during seismic activities, foraging significantly further from the survey vessel when in operation, while increasing their overall foraging effort. The birds reverted to normal behaviour when the operation ceased, although longer-term repercussions on hearing capacities cannot be precluded. The rapid industrialization of the oceans has increased lev...
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No-take zones may protect populations of targeted marine species and restore the integrity of marine ecosystems, but it is unclear whether they benefit top predators that rely on mobile pelagic fish. In South Africa, foraging effort of... more
No-take zones may protect populations of targeted marine species and restore the integrity of marine ecosystems, but it is unclear whether they benefit top predators that rely on mobile pelagic fish. In South Africa, foraging effort of breeding African penguins decreased by 30 % within 3 months of closing a 20-km zone to the competing purse-seine fisheries around their largest colony. After the fishing ban, most of the penguins from this island had shifted their feeding effort inside the closed area. Birds breeding at another colony situated 50 km away, whose fishing grounds remained open to fishing, increased their foraging effort during the same period.". This demonstrates the immediate benefit of a relatively small no-take zone for a marine top predator relying on pelagic prey. Selecting such small protected areas may be an important first conservation step, minimizing stakeholder conflicts and easing compliance, while ensuring benefit for the ecosystems within these habitats
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Drastic recent decreases in numbers of the Endangered African penguin Spheniscus demersus urge conservation efforts to reverse these trends. Habitat reduction due to former guano scraping forces penguins to breed in surface nests,... more
Drastic recent decreases in numbers of the Endangered African penguin Spheniscus demersus urge conservation efforts to reverse these trends. Habitat reduction due to former guano scraping forces penguins to breed in surface nests, vulnerable to predation by kelp gulls Larus dominicanus and extreme weather events. Here I compared gull predation and the success of penguins breeding in surface nests and two types of artificial nests before (2009) and after (2010-2011) the removal of predatory gulls from Bird Island, South Africa. Both culling gulls and artificial nests improved penguin chick survival, but post-culling chick survival was lower in surface nests than in artificial nests, suggesting a major impact of weather on chick mortality. Success of artificial nests was design-dependant, with poor hatching success in fibreglass burrows (probably due to high ambient temperatures), but nests under 50 cm cement pipes cut in half had the highest breeding success. Therefore, appropriately designed artificial nests can enhance African penguin breeding success, shielding them from both predation and extreme weather events. Where implementation of such nests is constrained, controlling kelp gulls can also enhance penguins’ production, especially during years of low food availability when chicks’ vulnerability to predation is exacerbated. Such strategy would, however, require ongoing management, as territories freed by culled gulls are constantly filled with new individuals. The alarming trend of the African penguin justifies strong conservation strategies, although these should also be concomitant with limiting oil spills and increasing food availability around their colonies.
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African penguins Spheniscus demersus naturally breed in guano burrows which provide shelter from predators and extreme weather conditions. Past guano harvesting has removed this habitat and artificial nests of different types have been... more
African penguins Spheniscus demersus naturally breed in guano burrows which provide shelter from predators and extreme weather conditions. Past guano harvesting has removed this habitat and artificial nests of different types have been deployed, with previous research identifying variable success of these different types. We investigated climate conditions in two types of artificial nests, and compared them to natural burrows and surface nests for two weeks in the incubation and early chick-rearing phases of the 2012 summer breeding season on Bird Island Algoa Bay, South Africa. We also compared breeding success since 2009 between some of these nest types. Natural burrows remained the best insulated from extremes of temperature and humidity, with temperatures consistently higher and humidity consistently lower than in exposed nests and the two types of artificial nests. Fibreglass nests retained temperatures >30°C, when Spheniscus penguins start being heat-stressed, for the longest periods of time. Sustained high temperatures will induce increased energy expenditure associated with active thermoregulation for birds in these nests. The combination of high temperatures and low humidity levels could also have contributed to damaging water-loss in the eggs and reduce egg survival, as suggested by the consistent lower hatching success in the fibreglass nests. Cement nests had more moderate temperatures than fibreglass nests and higher breeding success, possibly due to superior ventilation. Vegetation cover had no effect on the temperature regime inside fibreglass nests. To maximize conservation efforts for these endangered penguins, additional research should be conducted towards engineering artificial nests that better mimic the conditions of natural burrows.
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Industrial fishing can profoundly alter marine environments, and no-take zones are an important tool to achieve sustainable fishing and re-establish ecosystem integrity. However, the potential benefits for vagile species such as top... more
Industrial fishing can profoundly alter marine environments, and no-take zones are an important tool to achieve sustainable fishing and re-establish ecosystem integrity. However, the potential benefits for vagile species such as top predators are still questioned. The numbers of endangered African penguins Spheniscus demersus have halved since 2004. They depend on small pelagic fish, also targeted by a purse-seine industry in South Africa. We studied penguin foraging behaviour and breeding output at two colonies supporting 60% of the global population in relation to fishing activity by purse-seine vessels. In 2008, both sites were open to fishing, but in 2009 and 2010 waters within 20 km of the world’s largest colony were closed to fishing, while waters around the neighbouring colony, 50 km away, remained open. Birds’ foraging effort increased with the size of catches around their colonies and decreased with the implementation of a reserve. Total fishing catches in the bay remained constant, but shifted toward the boundaries of the reserve in 2010. While the no-take zone significantly reduced penguin foraging effort, intensified fishing pressure at the reserve boundaries (“fishing the line”) in 2010 limited this benefit. The decrease over time of both adult body mass and chick growth rates from both colonies, suggested that the 20 km-closure is too small to reverse penguin population decreases. Therefore, stronger fishery management measures, such as larger no-take zones, buffer zones around reserves, or local reduction of fishing quotas, seem necessary to increase food availability for penguins around their colonies. The collapse of Africa’s only breeding penguin species adds urgency to the wider implementation of such measures.
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Seabirds respond to environmental changes by adjusting their breeding and foraging strategies, but this behavioural flexibility has limits. Cape Gannets Morus capensis breeding in the southern Benguela on Malgas Island off South Africa’s... more
Seabirds respond to environmental changes by adjusting their breeding and foraging strategies, but this behavioural flexibility has limits. Cape Gannets Morus capensis breeding in the southern Benguela on Malgas Island off South Africa’s west coast have experienced large fluctuations in natural prey availability over the past decade, linked to environmental change and localised overfishing. When small pelagic fish are unavailable, breeding gannets increase their consumption of low-quality fishery discards (primarily hake Merluccius spp.). To investigate the limits of foraging flexibility of breeding gannets facing variable prey availability, foraging behaviour, nest attendance, adult body condition and chick growth were monitored between 2002 and 2012, along with diet composition and annual hydroacoustic assessments of prey abundance during the birds’ breeding season. The combined biomass of sardine Sardinops sagax and anchovy Engraulis encrasicolus within the Malgas gannet colony’s foraging range varied tenfold across the study period and was positively correlated with the proportion of these high quality fish in the gannets’ diet (17-90%). Foraging effort increased and nest attendance decreased with decreasing sardine/anchovy consumption. Adult body condition was negatively impacted by increases in hake in the diet. Chick growth was lowest when low sardine and anchovy composition was coupled with an increase in adult foraging effort, suggesting a limit to behavioural compensation for food shortages. This long-term study demonstrates the consequences of variable prey levels for Cape Gannet behaviour and fitness. It highlights the need for detailed investigations of seabird-fishery interactions, and the necessity to limit fishing within Cape Gannet foraging ranges during years of low natural prey abundance.
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Sex-biased mortality can increase the risk of extinction of threatened populations. Numbers of the Endangered African penguins Spheniscus demersus are decreasing rapidly and the smaller size of females associated with their higher... more
Sex-biased mortality can increase the risk of extinction of threatened populations. Numbers of the Endangered African penguins Spheniscus demersus are decreasing rapidly and the smaller size of females associated with their higher foraging effort during the breeding season may put them more at risk than males. Using records from 2004-2012 from a rehabilitation centre in South Africa, we investigated the sex ratio of African penguins that died at the centre within age-classes (adult, juvenile and chick) and causes of death (starvation, injury or oiling). The large majority of adult and juvenile birds at the centre died following starvation, rather than from injuries or oiling, and most of them (>60%) were females, while mortality of sexes was similar among chicks. Oiled birds received at the centre had high survival and release rates, hence sex-biased mortality could not be tested for oiled birds. Female-biased mortality in African penguins could skew adult sex ratio, which may further accelerate the rapid rate of decline of this endangered species.
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The number of African penguins Spheniscus demersus breeding in South Africa collapsed from about 56 000 pairs in 2001 to some 21 000 pairs in 2009, a loss of 35 000 pairs (> 60%) in eight years. This reduced the global population to 26... more
The number of African penguins Spheniscus demersus breeding in South Africa collapsed from about 56 000 pairs in 2001 to some 21 000 pairs in 2009, a loss of 35 000 pairs (> 60%) in eight years. This reduced the global population to 26 000 pairs, when including Namibian breeders, and led to classification of the species as Endangered. In South Africa, penguins breed in two regions, the Western Cape and Algoa Bay (Eastern Cape), their breeding localities in these regions being separated by ca. 600 km. Their main food is anchovy Engraulis encrasicolus and sardine Sardinops sagax, which are also the target of purse-seine fisheries. In Algoa Bay, numbers of African penguins halved from 21 000 pairs in 2001 to 10 000 pairs in 2003. In the Western Cape, numbers decreased from a mean of 35 000 pairs in 2001−2005 to 11 000 pairs in 2009. At Dassen Island, the annual survival rate of adult penguins decreased from 0.70 in 2002/03 to 0.46 in 2006/07; at Robben Island it decreased from 0.77 to 0.55 in the same period. In both the Western and Eastern Cape Provinces long-term trends in numbers of penguins breeding were significantly related to the combined biomass of anchovy and sardine off South Africa. However, recent decreases in the Western Cape were greater than expected given a continuing high abundance of anchovy. In the this province there was a southeast displacement of prey around 2000 and, after 2004, most trends in numbers breeding at localities generally matched those expected to follow this altered distribution, which led to a mismatch in the distributions of prey and some breeding localities of penguins.
In the southern Benguela upwelling ecosystem off the west coast of South Africa, seabird populations are decreasing dramatically because of reduced availability of pelagic fish. We tested the hypothesis that the west coast fishing... more
In the southern Benguela upwelling ecosystem off the west coast of South Africa, seabird populations are decreasing dramatically because of reduced availability of pelagic fish. We tested the hypothesis that the west coast fishing industry is competing for the remaining stocks of anchovy and sardine with the largest colony of Vulnerable Cape Gannets (Morus capensis) along the Atlantic coast. Using GPS-tracking of the birds, echo-sounding of pelagic fish, and vessel log books, we located overlap areas between bird foraging ranges, pelagic fish distribution, and fishing activities. We then compared fish catches by gannets and vessels within their joint foraging zones. In October 2007, purse-seine fishing grounds and gannet foraging areas overlapped by only 13%. However, for a 1-month period, the amount of fish removed from this area by purse-seine boats amounted to 41% of the food requirements of the 72,000 gannets breeding on Malgas Island (25% of the world population). The fishery’s catch in this area is significant in terms of its potential impact on gannets, but comprises only 3.6% of total fishery catch. Based on this finding, the rapidly decreasing size of the gannet colony and the stated objectives of South Africa’s Marine Living Resources Act of 1998, the case for considering and experimenting with at-sea ‘no-take’ areas for the purse-seine fishery is strong. Efforts to establish whether ‘no-take’ fishing zones increase food availability for top predators is an important next step in conservation of the Southern Benguela Ecosystem.
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Norwegian Northern Gannet Morus bassanus populations exhibit contrasted trends at a regional scale and several colony extinctions occurred in recent decades. In an attempt to understand the ecological drivers of such variability, we... more
Norwegian Northern Gannet Morus bassanus populations exhibit contrasted trends at a regional scale and several colony extinctions occurred in recent decades. In an attempt to understand the ecological drivers of such variability, we tested whether resource availability is a factor limiting the current development of gannetries in the Lofoten/Vesterålen area. Between 2007 and 2010, we recorded arrival and departure times of breeding gannets from two colonies from regions showing contrasting population growth rates during the past two previous decades. We also recorded the duration of joint attendances by gannet parents at the nest, performed opportunistic diet sampling and counted numbers of occupied nests. Finally, we compiled ring recoveries over a 30-year period to assess inter-colony movements. Norwegian gannet parents spent more time attending their chick together, with shorter foraging trips than those in growing British and French colonies of similar size, and their foraging effort was relatively low, despite some annual variations. Diet samples mainly constituted fish of high energetic value, such as large herring Clupea harengus and mackerel Scomber scombrus, and saithe Pollachius virens, prey that are relatively abundant within the study area. Ring data revealed, however, a northward movement of adults ringed as breeding birds and chicks from extinct Lofoten colonies, that established in a growing colony close to the North Cape. Recorded foraging features (trip duration, joint attendance and prey quality) during our study does not design food availability as a limiting factor explaining successive extinctions and re-colonisations of breeding sites in Lofoten/Vesterålen. White-tailed eagles Haliaeetus albicilla are known to predate opportunistically on Northern Gannet adult or chicks and their populations are growing in the Lofoten area. Their potential impact on the Norwegian Northern Gannet population dynamics should be further investigated.
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This account presents the first known observations of Cape Gannet Morus capensis fledgling mortalities as a result of aggressive nest defence behaviour by African Penguins Spheniscus demersus. Observations were conducted in 2013 on Bird... more
This account presents the first known observations of Cape Gannet Morus capensis fledgling mortalities as a result of aggressive nest defence behaviour by African Penguins Spheniscus demersus. Observations were conducted in 2013 on Bird Island, Algoa Bay, South Africa – the world’s largest breeding colony of Cape Gannets. Twenty-eight attacks were witnessed between 21 March and 18 May 2013 of which 16 resulted in mortality. The absence of previous observations of this phenomenon may be due to an unusually high proportion of African Penguin chicks being present relatively early on in the breeding season, associated with a potential for increased nest defence at this stage, and a larger number of gannet fledglings that year compared to previous years over the same period.
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World-wide fisheries generate large volumes of fisheries waste and it is often assumed that this additional food is beneficial for populations of marine top-predators. We challenge this concept via a detailed study of foraging Cape... more
World-wide fisheries generate large volumes of fisheries waste and it is often assumed that this additional food is beneficial for populations of marine top-predators. We challenge this concept via a detailed study of foraging Cape gannets Morus capensis and of their feeding environment in the Benguela upwelling zone. The natural prey of Cape gannets (pelagic fish) is depleted and birds now feed extensively on fishery wastes. These are beneficial for non-breeding birds, which show reduced feeding effort and high survival. In contrast breeding gannets double their diving effort in an attempt to provision their chicks predominantly with high-quality, live pelagic fish. Due to a scarcity of this resource they fail and most chicks die. Our study supports the Junk-food Hypothesis for Cape gannets since it shows that non-breeding birds can survive when complementing their diet with fishery wastes, but that they struggle to reproduce if live prey is scarce. This is due to the negative impact of low-quality fishery waste on the growth patterns of seabird chicks. Marine management policies should not assume that fishery waste is generally beneficial to scavenging seabirds, and that an abundance of this artificial resource will automatically inflate their populations.
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Oceanic structures such as mesoscale fronts may become hotspots of biological activity through concentration and enrichment processes. These fronts generally attract fish and may therefore be targeted by marine top-predators. In the... more
Oceanic structures such as mesoscale fronts may become hotspots of biological activity through concentration and enrichment processes. These fronts generally attract fish and may therefore be targeted by marine top-predators. In the southern Benguela upwelling system, such fronts might be used as environmental cues by foraging seabirds. In this study we analyzed high-frequency foraging tracks (GPS, 1 s sampling) of Cape gannets Morus capensis from two colonies located on the west and east coast of South Africa in relation to mesoscale fronts detected on daily high-resolution chlorophyll-a maps (MODIS, 1 km). We tested the association of (i) searching behavior and (ii) diving activity of foraging birds with mesoscale fronts. We found that Cape gannets shift from a transiting mode to an area-restricted search mode (ARS) at approximately 6.7 km (2-11 km) from fronts. This suggests that Cape gannets may be able to sense fronts (smell or vision) or other predators, and that such detection triggers an intensified investigation of their surroundings (i.e. ARS). Also we found that diving probability increases near fronts in 11 out of 20 tracks investigated (55%), suggesting that Cape gannets substantially use fronts for feeding; in the remaining cases, birds may have used other cues for feeding including fishing vessels, particularly for gannets breeding on the west coast. We thereby demonstrated that oceanographic structures such as mesoscale fronts are important environmental cues used by a foraging seabird within the rich waters of an upwelling system. There is now need for further investigations on how Cape gannets actually detect these fronts.
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Industrial-scale fisheries are often thought to reduce food availability for top predators. Estimating the spatial and temporal overlap over a fine scale between fisheries and predators during their breeding season, when their energy... more
Industrial-scale fisheries are often thought to reduce food availability for top predators. Estimating the spatial and temporal overlap over a fine scale between fisheries and predators during their breeding season, when their energy demand is greatest and when they are most spatially constrained is essential to understand and manage this potential impact on their populations. In the Benguela upwelling region, two endemic vulnerable seabirds, Cape gannets (Morus capensis) and African penguins (Spheniscus demersus) mainly eat anchovy (Engraulis encrasicolus) and sardine (Sardinops sagax), both of which are exploited by the purse-seine fishery. A recent eastward displacement of small pelagic fish off the South African coast has reduced fish availability for both birds and fisheries along the west coast. Using GPS-recorders, we studied the foraging dispersal of birds from eight colonies containing 95% of the global Cape gannet and 60% of the global African penguin populations to assess their overlap with fish catches. Despite the fact that bird data were gathered at very fine spatial and temporal scales (meters/hours), and fisheries data were recorded at much coarser spatial and temporal scales (20km/months), there was clear overlap in areas used. The main foraging areas of both species were located where purse-seine fisheries caught most fish, with most catches occurring during the birds’ breeding season. As birds and fisheries also overlap in the size of the targeted prey and the depth of exploitation, our study suggests the potential for intense competition between purse-seine fisheries and decreasing seabird populations in the southern Benguela. Long-term protection of these seabird species requires the inclusion of a suitable ecological buffer when setting fishery quotas, and implementing marine protected areas closed to fishing around key breeding sites and foraging hotspots may improve their breeding success.
Research Interests:
1. Climate change and overfishing impact marine ecosystems, potentially modifying the availability of small pelagic fish to marine top predators. Some seabirds that primarily rely upon these resources have switched to feeding on fishery... more
1. Climate change and overfishing impact marine ecosystems, potentially modifying the availability of small pelagic fish to marine top predators. Some seabirds that primarily rely upon these resources have switched to feeding on fishery wastes. It has therefore been argued that seabirds might become dependant upon this artificial resource.
2. To test this hypothesis we studied the foraging behaviour of Cape gannets (Morus capensis) breeding off South Africa using high resolution GPS tracking, in relation to the availability of pelagic fish assessed by acoustic at-sea surveys and fishing effort by the two main south African fisheries (purse seiners competiting with seabirds for pelagic fish, and trawlers producing fish wastes) tracked with Vessel Monitoring Systems. Conjoint seabird, fish and fisheries information were analysed at meso-(~100km) and sub-mesoscales (~10km) for years of high (2002), medium (2009) and low (2005) pelagic fish biomass within Cape gannet foraging range.
3. We found great inter-annual variability in spatial use by breeding Cape gannets, which was driven primarily by pelagic fish availability. At the mesoscale, birds and purse-seiners exploited similar marine areas, but no fine scale interactions were detected between birds and purse-seiners. Crucially, fine scale interactions between gannets and trawlers producing fishery wastes were only detected in 2005, when pelagic fish biomass was lowest, indicating a direct effect of trawlers on Cape gannet foraging behaviour in the absence of natural prey.
4. Further overlap analyses of gannet and trawler foraging areas during 2002-2010 confirmed that breeding birds only seek trawlers when pelagic fish availability is low, strongly suggesting reversible seabird dependency upon fishery waste.
5. Synthesis and applications. Our study demonstrates that seabirds such as Cape gannets depend on fishery wastes when their natural prey is scarce, but revert to feeding on natural resources whenever available, showing highly flexible foraging behaviour. These results have important implications in the context of the anticipated legislation banning at-sea disposal of fishery wastes in different regions, including European seas, highlighting the necessity to concomitantly increase natural prey availability for seabirds.
2. To test this hypothesis we studied the foraging behaviour of Cape gannets (Morus capensis) breeding off South Africa using high resolution GPS tracking, in relation to the availability of pelagic fish assessed by acoustic at-sea surveys and fishing effort by the two main south African fisheries (purse seiners competiting with seabirds for pelagic fish, and trawlers producing fish wastes) tracked with Vessel Monitoring Systems. Conjoint seabird, fish and fisheries information were analysed at meso-(~100km) and sub-mesoscales (~10km) for years of high (2002), medium (2009) and low (2005) pelagic fish biomass within Cape gannet foraging range.
3. We found great inter-annual variability in spatial use by breeding Cape gannets, which was driven primarily by pelagic fish availability. At the mesoscale, birds and purse-seiners exploited similar marine areas, but no fine scale interactions were detected between birds and purse-seiners. Crucially, fine scale interactions between gannets and trawlers producing fishery wastes were only detected in 2005, when pelagic fish biomass was lowest, indicating a direct effect of trawlers on Cape gannet foraging behaviour in the absence of natural prey.
4. Further overlap analyses of gannet and trawler foraging areas during 2002-2010 confirmed that breeding birds only seek trawlers when pelagic fish availability is low, strongly suggesting reversible seabird dependency upon fishery waste.
5. Synthesis and applications. Our study demonstrates that seabirds such as Cape gannets depend on fishery wastes when their natural prey is scarce, but revert to feeding on natural resources whenever available, showing highly flexible foraging behaviour. These results have important implications in the context of the anticipated legislation banning at-sea disposal of fishery wastes in different regions, including European seas, highlighting the necessity to concomitantly increase natural prey availability for seabirds.
Research Interests:
We compared the foraging ecology of Cape gannets (Morus capensis) attending two colonies of equivalent size, yet with contrasting diet and population trends. One colony, on the west coast of South Africa, is decreasing in size and its... more
We compared the foraging ecology of Cape gannets (Morus capensis) attending two colonies of equivalent size, yet with contrasting diet and population trends. One colony, on the west coast of South Africa, is decreasing in size and its occupants feed mainly on fishery wastes, whereas the other colony on the south coast of South Africa is growing and its occupants feed exclusively on natural prey (pelagic fish). In October and November 2005 we examined the diet, at-sea behaviour and energy requirements of breeding gannets using direct observations, miniaturised GPS loggers and time-depth recorders attached to foraging adults. Concurrent hydro-acoustic surveys allowed us to assess the distribution and abundance of their preferred prey (sardines Sardinops sagax and anchovies Engraulis encrasicolus). Birds from the declining, west coast colony foraged in areas containing very low abundances of pelagic fish. They fed primarily on low-energy fishery discards. They increased their foraging effort and exploited a greater area than birds from the growing colony, which took advantage of abundant pelagic fish stocks in their foraging range. A marked eastward shift of pelagic fish initiated in the late-1990s has resulted in the shortage of natural prey to Cape gannets on the west coast, strongly suggesting that the local population trend is driven by food availability during the breeding season. A bioenergetic model showed that enhanced availability of low-energy fishery waste does not seem to compensate for the absence of natural prey. Added to the predation pressure by Cape fur seals (Arctocephalus pusillus) and great white pelicans (Pelecanus onocrotalus), those threats weigh heavily on a vulnerable seabird population.
Research Interests:
Cameras fitted to marine top predators have already proved useful in exploring the mysteries of their lives offshore, in particular their diving behavior and group dynamics. Our pilot study – based on a limited number of individuals –... more
Cameras fitted to marine top predators have already proved useful in exploring the mysteries of their lives offshore, in particular their diving behavior and group dynamics. Our pilot study – based on a limited number of individuals – demonstrates that, in the context of managing global fisheries, cameras affixed to seabirds can be used to monitor seabird surroundings at sea, and potentially identify interactions between these threatened species and fishing vessels. In areas where “pirate” (illegal) fisheries occur, this technology may even allow remote identification and positioning of illegal fishing vessels
Research Interests:
We report co-operative group foraging in the African Penguin Spheniscus demersus. Groups of approximately 25 - 165 African Penguins were observed circling schools of pelagic fish, sometimes forcing them to the surface. During this... more
We report co-operative group foraging in the African Penguin Spheniscus demersus. Groups of approximately 25 - 165 African Penguins were observed circling schools of pelagic fish, sometimes forcing them to the surface. During this behaviour 66 - 75% of penguins were underwater at any given time. Smaller numbers of African Penguins also joined foraging groups of Cape Gannets Morus capensis and Cape Cormorants Phalacrocorax capensis, but did not appear to corral fish schools when outnumbered by these species. African Penguins are listed as Endangered due to ongoing rapid population decreases. If group foraging confers an advantage to African Penguins, their dwindling populations may suffer from an Allee effect as colonies become too small to support sufficient densities of birds for foraging groups to form.
Research Interests:
Breeding Spheniscus penguins are central place foragers that feed primarily on schooling pelagic fish. They are visual hunters, but it is unclear how they locate prey patches at a coarse scale. Many petrels and storm petrels... more
Breeding Spheniscus penguins are central place foragers that feed primarily on schooling pelagic fish. They are visual hunters, but it is unclear how they locate prey patches at a coarse scale. Many petrels and storm petrels (Procellariiformes), the penguins’ closest relatives, use olfactory cues to locate prey concentrations at sea, but this has not been demonstrated for penguins. Procellariiforms are attracted to a variety of olfactory cues, including dimethyl sulphide (DMS), an organosulphur compound released when phytoplankton is grazed, as well as fish odorants such as cod liver oil. A recent study found that African penguins Sphensicus demersus react to DMS on land. We confirm this result and show that African penguins also are attracted by DMS at sea. DMS-scented oil slicks attracted 2-3 times more penguins than control slicks, whereas penguins showed no response to slicks containing cod liver oil. Numbers of penguins attracted to DMS increased for at least 30 minutes, suggesting they could travel up to 2 km to reach scent cues. Repeats of land-based trials confirmed previous results showing DMS sensitivity for penguins on land. Our results also support the hypothesis that African penguins use DMS as an olfactory cue to locate prey patches at sea from a distance, which is particularly important given their slow commuting speed relative to flying seabirds.
Research Interests:
In variable environments, organisms are bound to track environmental changes if they are to survive. Most marine mammals and seabirds are colonial, central-place foragers with long-term breeding-site fidelity. When confronted with... more
In variable environments, organisms are bound to track environmental changes if they are to survive. Most marine mammals and seabirds are colonial, central-place foragers with long-term breeding-site fidelity. When confronted with environmental change, such species are potentially constrained in their ability to respond to these changes. For example, if environmental conditions deteriorate within their limited foraging range, long-lived species favour adult survival and abandon their current breeding effort, which ultimately influences population dynamics. Should poor conditions persist over several seasons, breeding-site fidelity may force animals to continue breeding in low-quality habitats instead of emigrating towards more profitable grounds. We assessed the behavioural response of a site-faithful central-place forager, the Cape gannet Morus capensis, endemic to the Benguela upwelling system, to a rapid shift in the distribution and abundance of its preferred prey, small pelagic shoaling fish. We studied the distribution and abundance of prey species, and the diet, foraging distribution, foraging effort, energy requirements, and breeding success of gannets at Malgas Island (South Africa) over four consecutive breeding seasons. Facing a rapid depletion of preferred food within their foraging range, Cape gannets initially increased their foraging effort in search of their natural prey. However, as pelagic fish became progressively scarcer, breeding birds resorted to scavenging readily available discards from a nearby demersal fishery. Their chicks cannot survive on such a diet, and during our four-year study, numbers of breeding birds at the colony decreased by 40% and breeding success of the remaining birds was very low. Such behavioural inflexibility caused numbers of Cape gannets breeding in Namibia to crash by 95% following over-fishing of pelagic fish in the 1970s. In the context of rapid environmental changes, breeding-site fidelity of long-lived species may increase the risk of local or even global extinction, rendering these species particularly vulnerable to global change.
Research Interests:
"Using a multi-disciplinary approach, we evaluated the potential consequences of long-term contrasting prey availability on the condition Cape gannets Morus capensis. We compared breeding adults from a decreasing colony on Malgas Island... more
"Using a multi-disciplinary approach, we evaluated the potential consequences of long-term contrasting prey availability on the condition Cape gannets Morus capensis. We compared breeding adults from a decreasing colony on Malgas Island off the west coast of South Africa, where the abundance of small pelagic fish has decreased, with an increasing colony on Bird Island off the south coast, where pelagic fish are more abundant. We investigated (1) pelagic fish density using data from a hydro-acoustic survey, (2) gannet diet (stomach content analyses, fatty acid and stable isotope analyses), (3) gannet foraging effort and at-sea feeding areas (nest attendance patterns, GPS-tracking and blood haematocrit), (4) chick growth rates, and (5) adult
body condition (morphometric measurements and breast muscle thickness). Our data confirmed contrasting prey availability between colonies, although pelagic fish were more abundant on the west coast than in previous years. Gannets exhibit dietary plasticity, feeding on pelagic fish and trawler discards, but favour natural prey when available. Stomach content samples showed that gannets from both islands mainly ate natural prey in 2009, but there were differences in their stable isotope and fatty acid signatures, supporting evidence of long-term diet differences. Nevertheless, chick growth rates and adult body condition were similar at both colonies, which was surprising for breeding adults from the west coast colony that had been feeding extensively on energy-poor fishery waste for several years. Breeding gannets' behavioural flexibility seems to have succeeded in maintaining body condition. However, this might have long-term costs, as adult survival at Malgas Island has decreased in recent years. Population decreases at this colony are exacerbated by low juvenile survival and perhaps differential recruitment to Bird Island. Higher foraging effort by adult breeding on the large colony of Bird Island compared to birds from the west coast, despite greater pelagic fish abundance on the south coast, probably suggests a greater intra-specific competition there. Monitoring of population
trends, population health indices and foraging behaviour, as well as prey availability is necessary to better understand the mechanisms underlying the population trends."
body condition (morphometric measurements and breast muscle thickness). Our data confirmed contrasting prey availability between colonies, although pelagic fish were more abundant on the west coast than in previous years. Gannets exhibit dietary plasticity, feeding on pelagic fish and trawler discards, but favour natural prey when available. Stomach content samples showed that gannets from both islands mainly ate natural prey in 2009, but there were differences in their stable isotope and fatty acid signatures, supporting evidence of long-term diet differences. Nevertheless, chick growth rates and adult body condition were similar at both colonies, which was surprising for breeding adults from the west coast colony that had been feeding extensively on energy-poor fishery waste for several years. Breeding gannets' behavioural flexibility seems to have succeeded in maintaining body condition. However, this might have long-term costs, as adult survival at Malgas Island has decreased in recent years. Population decreases at this colony are exacerbated by low juvenile survival and perhaps differential recruitment to Bird Island. Higher foraging effort by adult breeding on the large colony of Bird Island compared to birds from the west coast, despite greater pelagic fish abundance on the south coast, probably suggests a greater intra-specific competition there. Monitoring of population
trends, population health indices and foraging behaviour, as well as prey availability is necessary to better understand the mechanisms underlying the population trends."
Knowledge on how divers exploit the water column vertically in relation to water depth is crucial to our understanding of their ecology and to their subsequent conservation. However, information is still lacking for the smaller-bodied... more
Knowledge on how divers exploit the water column vertically in relation to water depth is crucial to our understanding of their ecology and to their subsequent conservation. However, information is still lacking for the smaller-bodied species, due mostly to size constraints of data-loggers. Here, we report the diving behaviour of a flying diving seabird, the Cape Cormorant Phalacrocorax capensis, weighing 1.0–1.4 kg. Results were obtained by simultaneously deploying small, high resolution and high sampling frequency GPS and time-depth loggers on birds breeding on islands off Western South Africa (34S, 18E) in 2008. In all, dive category was assigned to all dives performed by 29 birds. Pelagic dives occurred almost as frequently as benthic dives. Pelagic dives were shallow (mean: 5 m) and took place over seafloors 5–100 m deep. Benthic dives were deeper, occurring on seafloors mainly 10–30 m deep. Dive shape was linked to dive category in only 60% of dives, while the descent rate, ascent rate and bottom duration/dive duration ratio of a dive best explained its dive category. This shows that only the concomitant use of tracking and depth tags can adequately classify diving strategies in a diver like the Cape Cormorant. Diet was mainly Cape Anchovy Engraulis encrasicolis, suggesting that birds probably displayed two contrasted strategies for capturing the same prey. Flexible foraging techniques represent an important key to survival inside the highly productive but heterogeneous Benguela upwelling ecosystem.
Research Interests:
The Cape Cormorant Phalacrocorax capensis is unusual among cormorants in using aerial searching to locate patchily distributed pelagic schooling fish. It feeds up to 80 km offshore, often roosts at sea during the day, and retains more air... more
The Cape Cormorant Phalacrocorax capensis is unusual among cormorants in using aerial searching to locate patchily distributed pelagic schooling fish. It feeds up to 80 km offshore, often roosts at sea during the day, and retains more air in its plumage and is more buoyant than most other cormorants. Despite these adaptations to its pelagic lifestyle, little is known of its foraging ecology. We measured the activity budget and diving ecology of breeding Cape Cormorants. All foraging took place during the day, with 3.6±1.3 foraging trips per day, each lasting 85±60 min and comprising 61±53 dives. Dives lasted 21.2±13.9 s (max 70 s), attaining an average depth of 10.2±6.7 m (max 34 m), but variability in dive depth both within and between foraging trips was great. Within-bout variation in dive depth was greater when making shallow dives, suggesting that pelagic prey were targeted mainly when diving to <10 m. Diving ecology and total foraging time were similar to other cormorants, but the time spent flying (122±51 min.d-1, 14% of daylight) was greater and more variable than other species. Searching flights lasted up to 1 hour, and birds made numerous short flights during foraging bouts, presumably following fast-moving schools of pelagic prey. Compared to the other main seabird predators of pelagic fish in the Benguela region, Cape Gannets Morus capensis and African Penguins Spheniscus demersus, Cape Cormorants made shorter, more frequent foraging trips. Their foraging range while feeding small chicks was 7±6 km (max 40 km), similar to penguins (10-20 km) but less than gannets (50-200 km). Successful breeding by large colonies depends on the reliable occurrence of pelagic fish schools within this foraging range.
Research Interests:
African penguins (Spheniscus demersus) have experienced a 60% population decline in the past 30 years due to an eastward shift in the relative abundance of their main food source, anchovy (Engraulis encrasicolus) and sardine (Sardinops... more
African penguins (Spheniscus demersus) have experienced a 60% population decline in the past 30 years due to an eastward shift in the relative abundance of their main food source, anchovy (Engraulis encrasicolus) and sardine (Sardinops sagax). This shift may be exacerbated by pressure from the small-pelagic fishery targeting these species. A lack of knowledge regarding foraging areas when not breeding has been identified as a deficiency in
management planning for African penguins. Satellite transmitters were deployed on 20 adults during the pre-moult foraging period from colonies on the west coast (Dassen Island, n=10) and south coast (Bird Island, Algoa Bay, n=10) of South Africa. Kernel density analyses were produced using nightly locations to create foraging range maps, which were compared to catches made by the small-pelagic fishery during September-December 2012.
Birds from the two colonies differed in their foraging strategies. Compared to penguins from Bird Island, those from Dassen Island spent more than six times the number of nights beyond the foraging range used during the breeding season (40 km from their colony). Birds from Dassen Island typically made long, looping trips more than 300 km away from the colony, and travelled further and at higher daily rates to foraging areas than individuals from Bird Island, feeding outside areas where fishing activity was highest. Kernel density analysis showed the foraging range of Dassen Island penguins was between Cape Columbine and the
central Agulhas Bank. Individuals from Bird Island continued to central place forage,
typically staying within 35 km of the colony. Penguins from Dassen Island that remained on
the west coast had to compete with higher levels of fishing pressure than penguins from Bird
Island. More than 70% of the fleet-wide, 2012 purse-seine catch occurred within the area where Dassen Island penguins spent 50% of their time. These colony-specific characteristics
suggest that management plans for African penguins need to be regionally targeted and incorporate larger foraging ranges during the pre-moult period for birds from western colonies. The larger foraging ranges and effort demonstrated by birds from the west coast suggest that a combination of the low relative fish abundance and higher commercial fishing pressure may force pre-moulting birds to seek food sources farther from the colony, putting them at higher risk of not surviving the annual moult. This project requires more years of data to ensure these foraging patterns are representative, and to more accurately provide
management suggestions directed to alleviate stress on African penguins for long-term protection of this endangered seabird.
management planning for African penguins. Satellite transmitters were deployed on 20 adults during the pre-moult foraging period from colonies on the west coast (Dassen Island, n=10) and south coast (Bird Island, Algoa Bay, n=10) of South Africa. Kernel density analyses were produced using nightly locations to create foraging range maps, which were compared to catches made by the small-pelagic fishery during September-December 2012.
Birds from the two colonies differed in their foraging strategies. Compared to penguins from Bird Island, those from Dassen Island spent more than six times the number of nights beyond the foraging range used during the breeding season (40 km from their colony). Birds from Dassen Island typically made long, looping trips more than 300 km away from the colony, and travelled further and at higher daily rates to foraging areas than individuals from Bird Island, feeding outside areas where fishing activity was highest. Kernel density analysis showed the foraging range of Dassen Island penguins was between Cape Columbine and the
central Agulhas Bank. Individuals from Bird Island continued to central place forage,
typically staying within 35 km of the colony. Penguins from Dassen Island that remained on
the west coast had to compete with higher levels of fishing pressure than penguins from Bird
Island. More than 70% of the fleet-wide, 2012 purse-seine catch occurred within the area where Dassen Island penguins spent 50% of their time. These colony-specific characteristics
suggest that management plans for African penguins need to be regionally targeted and incorporate larger foraging ranges during the pre-moult period for birds from western colonies. The larger foraging ranges and effort demonstrated by birds from the west coast suggest that a combination of the low relative fish abundance and higher commercial fishing pressure may force pre-moulting birds to seek food sources farther from the colony, putting them at higher risk of not surviving the annual moult. This project requires more years of data to ensure these foraging patterns are representative, and to more accurately provide
management suggestions directed to alleviate stress on African penguins for long-term protection of this endangered seabird.
Seabirds respond to various forms of environmental change by adjusting breeding and foraging strategies, but these forms of behavioural flexibility have limits. Cape Gannets Morus capensis breeding on Malgas Island off the west coast of... more
Seabirds respond to various forms of environmental change by adjusting breeding and foraging strategies, but these forms of behavioural flexibility have limits. Cape Gannets Morus capensis breeding on Malgas Island off the west coast of South Africa and foraging in the surrounding waters of the southern Benguela have been subjected to large fluctuations in natural prey availability over the past decade. The distributions and abundances of pelagic fish in their foraging range have changed due to climate change, overfishing and/or natural variability. When their preferred prey (sardine Sardinops sagax and anchovy Engraulis encrasicolus) is unavailable, gannets consume other food items, including low-quality discards from the hake (Merluccius spp.) fishery. In order to determine the limits of flexibility in foraging effort of breeding gannets under contrasting environmental conditions, chick growth, nest attendance, adult body condition and foraging behaviour (trip duration, path length, and maximum distance foraged) were measured over the past decade, along with diet composition and hydroacoustic assessments of prey abundance and distribution. Pelagic fish biomass varied tenfold across the study period and was positively correlated with the proportion of sardine and anchovy in the gannets‟ diet, which ranged from 17-90%. All measures of foraging effort increased significantly with decreasing sardine and anchovy in the gannets‟ diet, while patterns of nest attendance (e.g. duration when both parents attended chicks, regularity of attendance bouts) improved significantly with increasing proportions of sardine and anchovy in the diet. Adult body condition was negatively impacted by increasing proportions of hake in the diet, while chick growth rates improved as the proportion of sardine and anchovy in the diet increased. Chick growth was dependent on a combination of diet composition, adult foraging effort (indicated by trip duration, which influences provisioning rates), and the regularity of parental shifts at the nest. Crucially, chick growth was lowest in years when gannet diet comprised < 50% sardine and anchovy and adults were forced to increase their foraging effort (likely due to the location and abundance of the fish), suggesting a limit to behavioural compensation for food shortages. This long-term study across varying environmental conditions has improved our knowledge of the responses of Cape Gannets to a changing oceanic environment. Such information can help predict potential population changes and better inform management strategies, such as the implementation of no-take fishing zones during years when gannet prey abundance is low. Furthermore, an understanding of the sensitivity of various life history traits to the severity of environmental conditions enhances the value of seabirds as indicators of ecosystem health.
Research Interests:
""Marine top predators play a pivotal role in stabilizing marine food webs. Their presence is also a good bio-indicator of the state of our oceans making them invaluable tools for detecting changes in the marine environment. However, it... more
""Marine top predators play a pivotal role in stabilizing marine food webs. Their presence is also a good bio-indicator of the state of our oceans making them invaluable tools for detecting changes in the marine environment. However, it is important to grasp a fundamental understanding of how predators integrate with their environment if we are to fully understand the link between top predators and lower trophic levels. Seabirds are top predators facing substantial threats from fisheries and climate change, thus understanding their ecology is of growing importance. Their life histories such as long life spans and late maturation have evolved as a means to cope with the heterogeneous ocean landscape and scarce prey availability. These birds have also evolved a suite of strategies to increase the probability of locating these scarce and patchy prey distributions. For instance, many seabirds, especially long ranged birds such as albatrosses and larger penguins, are hypothesized to utilize temperature gradients to locate meso-scale (100-1000 km) ocean physical features such as eddies, fronts and upwelling zones where nutrients are advected to the euphotic zone from deeper cool bottom waters. This nutrient injection drives productivity in the ocean making these features ideal feeding grounds for top predators. Seabirds are also capable of using olfactory cues and currents to locate these features. However on a fine to coarse scale (1-100 km) it is less understood how these predators locate patchy prey distributions where cues such as temperature may be ephemeral.
African Penguins have short foraging ranges (10-50 km), and forage in dynamic coastal environments making them an ideal model for understanding how short-ranged top predators locate their prey. By modeling the sea-surface thermal habitat preferences, and the dive behavior in relation to thermoclines of African Penguins I assess how these short-ranged birds use ocean physical processes to increase the probability of locating their small pelagic prey. African Penguins breeding on Bird Island, Algoa Bay, were capable of utilizing temperature as a potential cue to foraging in three-dimensions. Penguins commuted east and south of their colony likely predicting the occurrence of cool nutrient rich waters from a periodic upwelling cell. Penguins departed in the early morning travelling towards these areas, maximizing the time they foraged during the day in cooler waters with a higher probability of containing prey patches. Penguins used a correlated random search strategy during foraging suggesting that these birds were continuously searching for prey, and it is therefore likely that penguins are limited by the patchy distribution of prey rather than a heterogeneous marine environment. When diving, penguins’ utilized thermoclines as either a potential cue to prey or by association, as their prey may be scattered around thermoclines. Penguins dived deeper foraging below the thermocline when the thermocline depth increased and also responded in their dive behaviour under different thermocline structures. For instance, when thermoclines were a diffuse barrier to nutrients and less likely to concentrate prey, birds dived deeper towards the benthos. Warm water intrusions into the bay from the Agulhas Current resulted in birds diving deeper in search of cooler bottom waters.
This research also demonstrates the dual utility of bio-loggers as a method for generating accurate, high-resolution oceanographic data. These data can be used in future studies, generating a cross disciplinary platform for research. This thesis augments our knowledge base of the African Penguin. African Penguins show flexibility in their foraging behaviour by adjusting their dive behaviour to subsurface thermal structures. Penguins also demonstrated foraging optimization by using temperature cues and behavioral switching to maximize the probability of locating prey patches on a fine temporal and spatial scale. ""
African Penguins have short foraging ranges (10-50 km), and forage in dynamic coastal environments making them an ideal model for understanding how short-ranged top predators locate their prey. By modeling the sea-surface thermal habitat preferences, and the dive behavior in relation to thermoclines of African Penguins I assess how these short-ranged birds use ocean physical processes to increase the probability of locating their small pelagic prey. African Penguins breeding on Bird Island, Algoa Bay, were capable of utilizing temperature as a potential cue to foraging in three-dimensions. Penguins commuted east and south of their colony likely predicting the occurrence of cool nutrient rich waters from a periodic upwelling cell. Penguins departed in the early morning travelling towards these areas, maximizing the time they foraged during the day in cooler waters with a higher probability of containing prey patches. Penguins used a correlated random search strategy during foraging suggesting that these birds were continuously searching for prey, and it is therefore likely that penguins are limited by the patchy distribution of prey rather than a heterogeneous marine environment. When diving, penguins’ utilized thermoclines as either a potential cue to prey or by association, as their prey may be scattered around thermoclines. Penguins dived deeper foraging below the thermocline when the thermocline depth increased and also responded in their dive behaviour under different thermocline structures. For instance, when thermoclines were a diffuse barrier to nutrients and less likely to concentrate prey, birds dived deeper towards the benthos. Warm water intrusions into the bay from the Agulhas Current resulted in birds diving deeper in search of cooler bottom waters.
This research also demonstrates the dual utility of bio-loggers as a method for generating accurate, high-resolution oceanographic data. These data can be used in future studies, generating a cross disciplinary platform for research. This thesis augments our knowledge base of the African Penguin. African Penguins show flexibility in their foraging behaviour by adjusting their dive behaviour to subsurface thermal structures. Penguins also demonstrated foraging optimization by using temperature cues and behavioral switching to maximize the probability of locating prey patches on a fine temporal and spatial scale. ""