UC Marine Council
UC Office of the President
Title:
Dolphin sympatric ecology
Author:
Bearzi, Maddalena
Publication Date:
04-01-2005
Series:
Coastal Environmental Quality Initiative
Publication Info:
Coastal Environmental Quality Initiative, UC Marine Council, UC Office of the President
Permalink:
http://escholarship.org/uc/item/64f711gc
Additional Info:
To read final report of associated research supported by the California Coastal Environmental
Quality Initiative,follow this link: http://repositories.cdlib.org/ucmarine/ceqi/031/
Keywords:
Marine Mammal/Vertebrate Biology
Abstract:
Interspecific associations between two or more species of the family Delphinidae have been
reported by many scientists, but the sympatric ecology of such dolphin associations has not
been studied in great detail. A few field investigations have been conducted on this subject in
different parts of the world on species such as bottlenose dolphins (Tursiops spp.), short-beaked
common dolphins (Delphinus delphis ), and killer whales Orcinus orca ). Sympatric dolphins
seem to use different strategies to co-exist when resources appear to be limited, including dietary
divergence (different prey preference, slightly diverse diet,different feeding time) and/or different
habitat use shallow versus deep waters, flat areas versus submarine canyons and escarpments,
different travel routes). This paper presents a review of some well-studied dolphin species found
in sympatry and discusses the nature of habitat and resource partitioning as well as studies on
aggressive behaviour displayed by species living in the same habitat.
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Marine Biology Research, 2005; 1: 165 /175
REVIEW
Dolphin sympatric ecology
MADDALENA BEARZI
Department of Organismic Biology, Ecology and Evolution, University of California, Los Angeles, CA 90095-1606, USA
Abstract
Interspecific associations between two or more species of the family Delphinidae have been reported by many scientists, but
the sympatric ecology of such dolphin associations has not been studied in great detail. A few field investigations have been
conducted on this subject in different parts of the world on species such as bottlenose dolphins (Tursiops spp.), short-beaked
common dolphins (Delphinus delphis ), and killer whales (Orcinus orca ). Sympatric dolphins seem to use different strategies
to co-exist when resources appear to be limited, including dietary divergence (different prey preference, slightly diverse diet,
different feeding time) and/or different habitat use (shallow versus deep waters, flat areas versus submarine canyons and
escarpments, different travel routes). This paper presents a review of some well-studied dolphin species found in sympatry
and discusses the nature of habitat and resource partitioning as well as studies on aggressive behaviour displayed by species
living in the same habitat.
Key words: Dolphins, habitat partitioning, resource partitioning, sympatry
Introduction
The literature contains numerous accounts of associations and interactions between different species of
the family Delphinidae world-wide (Table I). Only a
few sympatric populations of small odontocetes,
however, have been well investigated in the field
(common bottlenose dolphins, Tursiops truncatus /
hereinafter bottlenose dolphin / and Indo-Pacific
bottlenose dolphins, Tursiops aduncus: Hale et al.
2000; Wang et al. 2000; short-beaked common
dolphins, Delphinus delphis , and bottlenose dolphins:
Politi et al. 1998; Bearzi et al. 2005; short-beaked
common dolphins, long-beaked common dolphins,
Delphinus capensis, and bottlenose dolphins: Bearzi
2003; short-beaked common dolphins and striped
dolphins, Stenella coeruleoalba : Frantzis & Herzing
2002; transient and resident killer whales, Orcinus
orca : Bigg et al. 1987, 1990; Baird et al. 1992; Baird
1994; Ford et al. 1998; Saulitis et al. 2000). In this
paper, sympatry is defined as the co-occurrence of
two or more dolphin species in the same immediate
habitat, which might be called direct sympatry, where
broad sympatry simply means two or more species
occurring over the same wider geographical area.
Interspecific associations between dolphins may
be beneficial for at least one species for several
reasons, particularly in offshore waters (e.g. increased feeding, decreased predation rates; Norris
& Dohl 1980; Baraff & Asmutis-Silvia 1998; Scott &
Cattanach 1998; Wilson 2000; Gygax 2001). The
goal of this paper is to review the present literature
on the sympatric ecology of some well-studied
dolphin species and discuss the different strategies
employed by these species to co-exist, reducing the
possible occurrence of direct competition for food
resources (Roughgarden 1976).
Sympatric ecology of some well-studied species
of Delphinidae
Field studies on dolphin sympatric associations have
been mentioned in the literature (Table II). This
paper presents a review of well-studied species found
in sympatry.
Bottlenose dolphins and Indo-Pacific bottlenose dolphins
Populations of bottlenose dolphins are known to
inhabit pelagic waters as well as coastal areas
(Leatherwood et al. 1983), showing morphological,
Correspondence: M. Bearzi, Department of Organismic Biology, Ecology and Evolution, University of California, Los Angeles, 621
Charles E. Young Drive South, Box 951606, Los Angeles, CA 90095-1606, USA. E-mail: mbearzi@earthlink.net
Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory,
University of Copenhagen, Denmark
(Accepted 7 April 2005; Printed 14 July 2005)
ISSN 1745-1000 print/ISSN 1745-1019 online # 2005 Taylor & Francis
DOI: 10.1080/17451000510019132
166
M. Bearzi
Table I. Accounts of associations and interactions between different species of the family Delphinidae observed in the field. For extensive
lists of cetaceans found in associations in the eastern Pacific Ocean and the Gulf of California, also see Hill & Barlow (1992), Carretta &
Forney (1993), Mangels & Gerrodette (1994), Carretta et al. (1995), Frantzis & Herzing (2002).
Species
Globicephala macrorhynchus , Tursiops truncatus ,
Lagenorhynchus obscurus , Orcinus orcas
Stenella attenuata , Stenella longirostris
Tursiops aduncus , Sousa chinensis
Stenella coeruleoalba , Delphinus delphis
L. obscurus , Grampus griseus
Globicephala melas , O. orcas
D. delphis , Delphinus capensis
Lagenorhynchus acutus , D. delphis , G. melas
T. truncatus , S. chinensis
O. orcas , other Delphinidae
Globicephala sp., D. delphis
D. delphis , T. truncatus
G. macrorhynchus , G. griseus
G. griseus , Lagenorhynchus obliquidens , Lagenorhynchus hosei ,
Lagenorhynchus borealis , Phocoenoides dalli
T. truncatus , Phocoena phocoena
G. macrorynchus , D. capensis
G. macrorynchus , Peponocephala electra
Stenella frontalis , T. truncatus
G. melas , L. acutus
S. coeruleoalba , D. delphis , G. griseus
osteological, and molecular differentiations (Walker
1981; LeDuc & Curry 1998; Rossbach & Herzing
1999). The frequent presence of bottlenose dolphins
along the coastline has made this dolphin one of the
best-known cetaceans (e.g. Shark Bay, western Australia: Connor & Smolker 1985; Connor et al. 1998;
the Firth of Tay, Scotland: Wilson et al. 1993; Wilson
1995; Sarasota Bay, Florida: Scott et al. 1990; Wells
1991; Argentine Bay: Würsig 1978; Croatia, Mediterranean Sea: Bearzi et al. 1997, 1999; and in
southern California: Weaver 1987; Hansen 1990;
Weller 1991; Defran et al. 1999). Coastal populations
usually live in small groups (five to 25 individuals)
within 1 km of the shore and often reside in a specific
area, whereas pelagic populations are found in larger
schools (25/150 individuals) in the open ocean
(Bearzi et al. 1999; Defran & Weller 1999).
Sympatric species of the genus Tursiops have been
described by a few investigators. For instance, bottlenose dolphins and Indo-Pacific bottlenose dolphins appeared to be in direct sympatry around the
Chinese waters of the Penghu archipelago and were
Reference
Norris & Prescott 1961
Perrin et al. 1973
Norris & Dohl 1980
Norris et al. 1994
Ballance & Pitman 1998
Saayman & Tayler 1973
Au et al. 1979
Au & Perryman 1985
Polacheck 1987
Forcada et al. 1994
Das et al. 2000
Garcı́a et al. 2000
Würsig & Würsig 1980
Bloch & Lockyer 1988
Leatherwood et al. 1988
Hill & Barlow 1992
Bearzi 2003
Selzer & Payne 1988
Gowans & Whitehead 1995
Corkeron 1990
Jefferson et al. 1991
Overholtz & Waring 1991
Bearzi 1997
Bruno et al. 2004
Shane 1995
Shelden et al. 1995
Ross & Wilson 1996
Weller et al. 1996
Migura & Meadows 2002
Herzing & Johnson 1997
Baraff & Asmutis-Silvia 1998
Frantzis & Herzing 2002
observed in mixed schools that frequently included
other dolphin species as well (Yang 1976; Zhou &
Qian 1985). These two species, however, differed
ecologically: bottlenose dolphins preferred the coastal
and shallow waters of the continental shelf, feeding
upon benthic or reef-dwelling fish and cephalopods,
whereas Indo-Pacific bottlenose dolphins favoured
offshore waters, feeding mostly on schooling epipelagic and mesopelagic species (Wang et al. 2000).
In the Indian and western Pacific Oceans, Hale et
al. (2000) recorded different preferences in habitat
choice for the same species, with bottlenose dolphins
frequenting both shallow waters and offshore reefs
and Indo-Pacific bottlenose dolphins inhabiting
estuaries and coastal waters. This study showed
that some areas were occupied exclusively by one
species, with coastal regions of sympatry in their
distribution.
Sympatric bottlenose dolphins and Indo-Pacific
bottlenose dolphins also seemed to exist in south
African waters (Wang et al. 2000), although Ross
(1977) described these species as being typically
A review of well-studied sympatric dolphins
167
Table II. Field studies of sympatric associations of the family Delphinidae.
Species
Site
O. orca (transient and resident)
Eastern North Pacific
Reference
Baird 1994
Baird et al. 1992
British Columbia
Baird & Dill 1995, 1996
Vancouver Island
Bigg 1982
Baird & Whitehead 2000
British Columbia and Alaska
Barrett-Lennard et al. 1996
British Columbia and Washington State
Bigg et al. 1987, 1990
Coastal British Columbia and adjacent waters
Ford et al. 1998
British Columbia
Guinet 1990
Morton 1990
Prince William Sound (Alaska)
Saulitis et al. 2000
T. truncatus and T. aduncus
Indian and western Pacific oceans
Hale et al. 2000
Taiwan and south-central China (Chinese waters) Wang et al. 2000
D. delphis and D. capensis
Santa Monica Bay (California)
Bearzi 2003
Southern California Bight (eastern north Pacific) Banks & Brownell 1969
Evans 1975
Heyning & Perrin 1994
Rosel et al. 1994
California coast
Hill & Barlow 1992
Eastern north Pacific and adjacent waters
Leatherwood et al. 1988
Eastern Pacific
Perrin et al. 1985
L. acutus and D. delphis
Scotian shelf (Nova Scotia)
Gowans & Whitehead 1995
L. acutus , D. delphis , and G. melas
Northeastern USA
Selzer & Payne 1988
S. coeruleoalba and D. delphis
Eastern tropical Pacific
Au et al. 1979
Au & Perryman 1985
Polacheck 1987
Biscay Bay (northeast Atlantic)
Das et al. 2000
Southeastern coast of Spain
Sagarminaga & Cañadas 1995, 1998
S. coeruleoalba , D. delphis , and G. griseus
Gulf of Corinth (Greece, Mediterranean Sea)
Frantzis & Herzing 2002
S. longirostris and S. attenuata
Hawaii (eastern tropical Pacific)
Norris & Dohl 1980
Norris et al. 1994
Perrin et al. 1973
Psarakos et al. 2003
Western tropical Indian Ocean
Ballance & Pitman 1998
S. longirostris , S. attenuata , and T. truncatus Hawaii
Baird et al. 2001
S. longirostris and Lagenodelphis hosei
Central Philippines
Dolar 1999
S. attenuata and T. truncatus
Bahamas waters
Herzing & Johnson 1997
G. macrorhynchus and D. delphis
Eastern tropical Pacific
Polacheck 1987
G. macrorhynchus and T. truncatus
Northeastern Pacific
Norris & Prescott 1961
G. macrorhynchus and G. griseus
Santa Catalina Island (California)
Shane 1995
T. truncatus and D. delphis
Kalamos Island (Greece)
Ferretti et al. 1998
Politi 1998
Politi et al. 1998
Bruno et al. 2004
T. truncatus , D. delphis ,
S. coeruleoalba and Sousa sp.
Cape coast of south Africa
Saayman et al. 1972
allopatric. Ross (1977) noted different prey in the
stomachs of bottlenose dolphins and Indo-Pacific
bottlenose dolphins, with the former species exploiting deep reefs located offshore and the latter
preferring shallow inshore waters.
Short-beaked common dolphins in associations with longbeaked common dolphins, bottlenose dolphins, and
striped dolphins
Inshore populations of the genus Delphinus have
been described for different areas world-wide, including the Southern California Bight, California
(Evans 1975; Bearzi 2003), South Africa (Young &
Cockroft 1994), Bay of Plenty, New Zealand (Neumann 2001a,b) and the Mediterranean Sea (Bruno
et al. 2004; Bearzi et al. 2005), whereas the ecology
of offshore communities remains largely unknown
(Evans 1994). Several populations of common
dolphins stay in large schools that can reach thousands of individuals, but often separate into smaller
basic social units of about 30 individuals (Evans
1994; Bearzi et al. 2003).
There is no known gene flow between shortbeaked common dolphins and long-beaked common
dolphins, and they occur sympatrically in tropical
168
M. Bearzi
and temperate waters (Heyning & Perrin 1994; Rice
1998).
In Santa Monica Bay, California, the direct
sympatric ecology of short-beaked common dolphins and long-beaked common dolphins was investigated (Bearzi 2003). The two species were both
observed year-round mostly offshore (/500 m from
shore), generally near submarine escarpments and
canyons. Short-beaked common dolphins and longbeaked common dolphins were sympatric in the bay,
but they were never seen in mixed schools (Bearzi
2003). The co-existence of these species is probably
explained by an abundance of anchovies (Engraulis
mordax ), among their favourite food, and other prey
in areas of local upwelling such as submarine
canyons and escarpments, as also reported by other
authors (Mais 1974; Evans 1975; Hui 1979). These
sympatric species had a similar diet (Fitch &
Brownell 1968). However, slight differences in their
prey were observed (Schwartz et al. 1992). This
difference in diet might indicate how partitioning of
ecological niches may have reduced the occurrence
of competition for food resources when the dolphins
were in direct sympatry (Bearzi 2003).
In the same bay, the broad sympatric ecology of
bottlenose dolphins, short-beaked common dolphins
and long-beaked common dolphins was also investigated (Bearzi 2003). High abundance and yearround occurrence of the three species appeared to
be correlated to prey abundance and, consequently,
to the oceanography of this region (Bearzi 2003), as
also reported for other small odontocetes in different
locations (Cockcroft & Peddemors 1990; Gowans &
Whitehead 1995; Defran et al. 1999). Eighty per cent
of the sightings of bottlenose dolphins (n /157) were
found in shallow waters (B/500 m from shore), and
they were generally separated from the distribution of
the two species of common dolphins showing spatial
habitat partitioning (Bearzi 2003). A few sightings of
feeding bottlenose dolphins, however, were recorded
near the deepest submarine canyons, in similar
feeding locations of the two species of common
dolphins. Considering that bottlenose dolphins and
the two species of common dolphins generally fed on
different prey (for a review of preys consumed by the
three Delphinidae : Bearzi 2003), these species were
likely to have co-occurred at these locations without
competition for resources (Bearzi 2003).
Das et al. (2000) also reported slightly different
dietary preferences for sympatric striped dolphins
and short-beaked common dolphins in the northeast
Atlantic (Bay of Biscay). In this area, both species
were quite opportunistic feeders, taking advantage of
seasonally or locally abundant preys. However,
striped dolphins were observed displaying more
opportunistic trophic habits compared with common dolphins.
Habitat partitioning and direct sympatry have
been observed for short-beaked common dolphins
and other delphinids by Gowans & Whitehead
(1995). These authors examined the summer distribution of short-beaked common dolphins, Atlantic white-sided dolphins (Lagenorhyncus acutus ), and
long-finned pilot whales (Globicephala melas ) in the
highly productive waters in and near a submarine
canyon of the Scotian Shelf called the Gully. Their
results demonstrated that: (1) these species were
much more abundant inside the Gully than outside,
and (2) they used some areas of the Gully slightly
differently, showing spatial partitioning of habitat.
Atlantic white-sided dolphins and short-beaked
common dolphins divided the Gully temporally but
not geographically, whereas pilot whales ranged
widely over the entire study site, preferring locations
with flat relief.
Habitat partitioning and direct sympatry were also
observed for short-beaked common dolphins and
bottlenose dolphins in the eastern Ionian Sea near
the island of Kalamos, where a small group of
bottlenose dolphins shared the same inshore waters
of the archipelago with about 100 short-beaked
common dolphins (Politi et al. 1998; Bruno et al.
2004). These two sympatric species had adopted
different foraging strategies, with common dolphins
feeding in the water column or near the surface and
bottlenose dolphins focusing on bottom prey (Ferretti et al. 1998). In spite of such sympatry, the two
species rarely mixed and showed no direct interactions (Bearzi et al. 2005). These results suggested a
separation of niches that may have reduced direct
competition for food resources (Bruno et al. 2004).
Sympatric short-beaked common dolphins and
striped dolphins have been observed in three different areas of the Mediterranean: Alborean Sea
(Garcia et al. 2000), south Tyrrhenian Sea (Mussi
et al. in press) and Gulf of Corinth (Frantzis &
Herzing 2002). Frantzis & Herzing (2002) also
observed striped dolphins and short-beaked common dolphins in mixed-species associations with
Risso’s dolphins (Grampus griseus ). In all mixedspecies sightings, Risso’s dolphins and common
dolphins were always the minority species present
and interspecific rake marks on Risso’s dolphins
indicated potentially complex and regular interspecific interactions among these species. Among the
accountable factors for mixed-species associations in
the Mediterranean Sea there were: (1) the relative
abundance of each species, and (2) the potential
dependence of common dolphins on striped
dolphins when the former could not form singlespecies groups (Frantzis & Herzing 2002).
A review of well-studied sympatric dolphins
Transient and resident killer whales
In the eastern north Pacific, two forms of killer
whales, resident and transient, are distinguished
(Bigg 1982; Baird & Dill 1995). These whales
concentrate in cold regions of high productivity in
which pods occupy very large ranges (Baird 2000).
Groups of this species generally occur in small pods,
usually with less than 40 individuals (Dahlheim &
Heyning 1999), and resident pods are typically larger
than transient pods (Bigg et al. 1987; Morton 1990;
Baird 1994). Residents and transients show differences in acoustics, morphology, pigmentation patterns, and genetics (Barrett-Lennard et al. 1996; Ford
et al. 1998; Baird 2000). Besides significant differences, these populations are well known to live
sympatrically (Table II).
In British Columbian and Washington waters, two
communities of northern and southern resident killer
whales live in broad sympatry with transient killer
whales while displaying remarkable differences in
feeding behaviour (Baird 2000; Saulitis et al. 2000).
Resident populations feed primarily on fish, while
transient whales prey on marine mammals, mainly
pinnipeds (Bigg et al. 1990; Ford et al. 1998; Saulitis
et al. 2000). Bigg et al. (1990) and Ford et al. (1998)
observed that resident killer whales of British Columbia, Washington and Alaska, eat mostly salmonids, of which 50% were chinook (Oncorhynchus
tshawytscha ), the largest and most energy-rich species
present year-round in these areas. Similarly, resident
killer whales in Prince William Sound, Alaska, fed
primarily on coho salmon (Oncorhynchus kisutch ),
while transient killer whales fed on harbour seals
(Phoca vitulina ) and Dall’s porpoises (Phocoenoides
dalli ; Saulitis et al. 2000).
In the various study areas, transients travel and
forage more than residents (88.5 /94.5 versus 58 /
72% of the time), whereas residents socialize and
rest more than transients (Morton 1990; Felleman et
al. 1991; Baird 1994; Saulitis et al. 2000). Saulitis et
al. (2000) also reported that different prey choices
among populations of killer whales were accompanied by different foraging strategies. Residents, for
instance, foraged in co-ordinated pods swimming at
high speed, lunging, encircling and chasing fish at the
surface (Similä & Ugarte 1993; Barrett-Lennard et al.
1996); mammal-eating transients either swam along
shorelines or in dispersed formation across open areas
(Barrett-Lennard et al. 1996; Saulitis et al. 2000).
Baird & Dill (1995) found high variability in
habitat use between resident and transient whales,
with transient animals spending far more time in
shallow waters. Dissimilarities also existed in diving
patterns of these populations, with resident animals
spending most of their time in the top 20 m of the
169
water column and feeding on salmonids, with transient animals displaying longer mean dive durations
between 20 and 60 m (Bigg et al. 1990; Baird 1994,
2000).
Associations between transient and resident killer
whales have rarely been seen (Morton 1990; Baird &
Dill 1995; Barrett-Lennard et al. 1996). Observations in Prince William Sound and coastal British
Columbia show that these populations do not
associate, probably because of their strikingly different diet (Ford et al. 1998; Saulitis et al. 2000).
Ecological separation within sympatric dolphin
communities
When species that require similar resources occur in
the same habitat they tend to partition the available
resources, thus reducing competition (Roughgarden
1976). Two or more competing species usually
divide the resources by occupying different physical
locations or by feeding on different prey (Roughgarden 1976; Pianka 1978). These strategies have
been observed for a large number of taxa, including
primates (Jones & Sabater-Pi 1971; Tutin & Fernandez 1984; Kuroda et al. 1996; Yamagiwa et al.
1996; Stanford & Nkurunungi 2003) and carnivores
(Wu 1999; Fedriani et al. 2000; Wang & Fuller
2001). In-depth field investigations of habitat partitioning and resource use for small odontocetes are
complicated due to the difficulties of observing these
animals in the open ocean, but comparative inferences can be formulated based on existing studies.
Strategies adopted by sympatric species to co-exist
Investigations on a few sympatric species of the
family Delphinidae conducted world-wide illustrate
how these animals seem to adopt similar strategies to
co-exist (Table III) and show that ecological separation between sympatric species is based primarily on
diet and habitat use.
Dietary divergence within habitat. When food is
abundant, different dolphin species with overlapping
diets may be found together in the same habitat
(Selzer & Payne 1988; Gowans & Whitehead 1995).
The prey may come in schools large enough to
accommodate mixed-species aggregations of predators and complete dietary overlap at certain times,
but such large prey patches are not consistent
enough to support these overlaps all the time
(Tarasevich 1957; Bearzi 2003). In situations where
diets frequently overlap but food cannot support
competing predators, it appears that sympatric
species tend to exhibit different prey preferences
(Gowans & Whitehead 1995). Many species of small
170
M. Bearzi
Table III. Ecological separation within sympatric dolphin communities.
Trait
Dietary divergence within habitat
Different prey preference
Species and location
O. orca (transients and residents),
British Columbia, Alaska, and
Washington State
D. delphis , T. truncatus ,
Kalamos Island (Greece)
Diet overlap/slightly different diet
Diet overlap/different seasons or time
Tursiops sp.,
various areas around the world
D. delphis , S. coeruleoalba ,
Northeast Atlantic
D. delphis, D. capensis ,
Santa Monica Bay (California)
L. acutus , D. delphis ,
Globicephala melas ,
Scotian shelf (Nova Scotia)
L. acutus , D. delphis , Continental shelf
of the northeastern USA
L. acutus, D. delphis , G. melas,
Scotian shelf (Nova Scotia)
S. longirostris , S. attenuata ,
Hawaii (eastern tropical Pacific)
S. longirostris , S. attenuata ,
Eastern tropical Pacific
Different habitat use
Shallow versus deep waters, and/or
inshore versus offshore populations
Flat areas versus steeper areas
Reference
Bigg et al. 1990
Felleman et al. 1991
Baird 2000
Saulitis et al. 2000
Ferretti et al. 1998
Politi et al. 1998
Hale et al. 2000
Das et al. 2000
Bearzi 2003
Gowans & Whitehead 1995
Selzer & Payne 1988
Gowans & Whitehead 1995
Norris & Dohl 1980
Norris et al. 1994
Perrin et al. 1973
O. orca (transients and residents),
British Columbia and Washington State Baird & Dill 1995
Baird 1994, 2000
D. delphis , D. capensis and
T. truncatus ,
Santa Monica Bay (California)
Bearzi 2003
D. delphis , T. truncatus ,
Kalamos Island (Greece)
Ferretti et al. 1998
Politi et al. 1998
Bruno et al. 2004
T. truncatus and T. aduncus ,
Chinese waters
Wang et al. 2000
T. truncatus , Sousa sp., and
S. coeruleoalba ,
southeastern Cape coast of South Africa Saayman et al. 1972
S. longirostris , S. attenuata ,
Hawaii (eastern tropical Pacific)
Perrin et al. 1973
Norris & Dohl 1980
Norris et al. 1994
S. longirostris , S. attenuata ,
T. truncatus , Hawaii
Baird et al. 2001
S. longirostris , Lagenodelphis hosei ,
Central Philippines
Dolar 1999
Dolar et al. 2003
S. coeruleoalba , D. delphis ,
southeastern coast of Spain
Sagarminaga & Cañadas 1995
L. acutus, D. delphis , G. melas ,
Scotian shelf (Nova Scotia)
Gowans & Whitehead 1995
Different travel routes related to bottom
topography
O. orca (transients and residents),
British Columbia and Washington State Morton 1990
Felleman et al. 1991
Baird 2000
A review of well-studied sympatric dolphins
odontocetes, such as short-beaked common dolphins and bottlenose dolphins, are well known to
be opportunistic feeders that can vary their diet
according to the availability of the most abundant
and catchable prey (Evans 1975, 1994; Klinowska
1991). A small difference in prey preference may be
enough to support the feeding requirements of more
than one species, allowing sympatric dolphins to coexist (Hoelzel 1998).
Slightly different diets for sympatric striped dolphins and short-beaked common dolphins were
observed by Das et al. (2000) in the northeast
Atlantic (Bay of Biscay). Ross (1977) reported
more striking differences in prey preferences for
sympatric bottlenose dolphins for the Indian and
western Pacific Ocean. However, sympatric species
of the family Delphinidae can also show a completely
different diet, as illustrated for resident and transient
killer whales (Bigg et al. 1990; Baird 2000).
In addition to differences in prey preferences,
sympatric dolphin species can show dietary separation in times of day and/or during different times of
year (Table III). This behaviour was observed for
Atlantic white-sided dolphins and short-beaked
common dolphins in the Gully (differences in times
of year as well as prey depth and species: Gowans &
Whitehead 1995) and for spotted dolphins (Stenella
attenuata ) and spinner dolphins (Stenella longirostris )
in the eastern tropical Pacific (differences in times of
day as well as prey depth, size and species: Perrin et
al. 1973).
Different habitat use. Sympatric dolphins may also
use the same microhabitat in a different way, such as
exploiting resources found at different depths (Table
III). A separation of niches based on depth was
proposed in the eastern Ionian Sea for bottlenose
and short-beaked common dolphins (Ferretti et al.
1998; Politi et al. 1998).
Sympatric species can also display ecological
separation utilizing inshore and offshore waters, as
observed by Wang et al. (2000) for bottlenose
171
dolphins living in Chinese waters, Dolar (1999) for
spinner dolphins and Fraser’s dolphin (Lagenodelphis
hosei ) in the Sulu Sea, Bearzi (2003) for bottlenose
dolphins in sympatry with short-beaked common
dolphins in Californian waters, and Baird & Dill
(1995) for transient and resident killer whales in
British Columbia and Washington State. Resident
and transient killer whales also used the same habitat
but with different travel routes, sometimes related to
the bottom topography (Morton 1990; Felleman et
al. 1991; Baird 2000).
Aggressive behaviour and competition between sympatric
species
Direct competition and aggressive behaviour between sympatric species of the family Delphinidae
have only occasionally been observed (Table IV).
Ross & Wilson (1996) witnessed four violent
dolphin/porpoise interactions in the Moray Firth,
Scotland, but these authors did not discuss possible
reasons for these interactions. In the same study
area, Patterson et al. (1998) recorded aggressive
behaviour by sympatric bottlenose dolphins towards
harbour porpoises, suggesting that infanticide may
be a factor responsible for this type of behaviour.
Baird (1998) also reported aggressive behaviour by a
Pacific white-sided dolphin on a neonatal harbour
porpoise in Washington State. His study showed that
aggression was more the result of an object-oriented
play than aggressive behaviour displayed by one
species competing for food, mate, or space. In the
western edge of Great Bahama Bank, Herzing et al.
(2003) observed interspecific interactions between
Atlantic spotted dolphins (Stenella frontalis ) and
bottlenose dolphins, with male spotted dolphins
displaying dominant mounting behaviour towards
bottlenose dolphin males. In Hawaiian waters,
Psarakos et al. (2003) also observed aggressive
behaviour between sympatric spinner and spotted
dolphins. This type of interaction was accompanied
by interspecific copulation.
Table IV. Aggressive behaviour between sympatric dolphins.
Aggressive behavioura
Aggressors
Location
References
Victims
T. truncatus
P. phocoena
Moray Firth (Scotland)
L. obliquidens
S. frontalis
S. longirostris
G. griseus
P. phocoena
T. truncatus
S. attenuata
S. coeruleoalba
D. delphis
G. melaena
San Juan Island (Washington State)
Great Bahama Bank, Bahamas
Hawaii (eastern tropical Pacific)
Gulf of Corinth, Greece
Ross & Wilson 1996
Patterson et al. 1998
Baird 1998
Herzing et al. 2003
Psarakos et al. 2003
Frantzis & Herzing 2002
Santa Catalina Island, California
Shane 1995
G. griseus
a
This list does not include predatory /prey mixed-species interactions observed for transient killer whales feeding on small cetaceans.
172
M. Bearzi
It is clear that by contrasting these infrequent
examples of interactions, the majority of the investigations conducted world-wide to date show that
dolphins tend, whenever possible, to avoid direct
competition by using behavioural, dietary and physiological habitat specializations (Table II).
Future research: do sympatric associations
among dolphins reflect social complexity?
Species such as bottlenose dolphins and short-beaked
common dolphins exhibit a fission /fusion grouping
pattern (Connor et al. 2000; Bruno et al. 2004) in
which proximate changes in group size and composition appear to reflect proximate availability and distribution of food resources. The key factor that may
account for this grouping in dolphins is usually prey,
the occurrence of which is ephemeral and patchy,
particularly in offshore waters (Clapham 1993).
Dolphins also exhibit high levels of encephalization, having the largest brain-to-body size ratio
among the cetaceans (Reiss et al. 1997; Marino
1998; Marino et al. 2000). Such encephalization
may enable these animals to forage for widely
dispersed, frequently changing food sources, and to
cope with the complexities of group life that follow
from such a fluid foraging pattern (Würsig 1978;
Würsig & Würsig 1980). If fission /fusion grouping is
a response to a complex foraging environment and
has placed intelligence and social complexity at a
premium in these animals, how may it have affected
sympatric associations? Ecological information about
sympatric dolphins is scarce in comparison with other
large brained species such as great apes (Bearzi 2003).
Because dolphins’ ecological problem-solving needs
and abilities parallel those of great apes (Marino
1996, 1998; Reiss et al. 1997) it is possible that
similar strategies that rely on cognition and memory
have facilitated divergence of foraging strategies when
in sympatry with other cetacean species.
Acknowledgements
The manuscript was improved through review by
W. Hamner, J. Heyning, G. Grether, G. Bearzi,
B. Schlinger, C. Saylan, and C. Stanford. This study
was conducted under the Coastal Environmental
Quality Graduate Fellowship. Special thanks to the
Los Angeles Dolphin Project volunteers.
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