Orcaella heinsohni (Beasley,
Robertson and Arnold, 2005)
English: Australian snubfin dolphin
German: Australischer Stupsflossen-Delphin
Spanish: Delfín a aleta chata de Australia
French: Dauphin à aileron retroussé d'Australie
Orcaella heinsohni © Wurtz-Artescienza (see links).
The Australian snubfin dolphin resembles the Irrawaddy dolphin
brevirostris), but, as opposed to its congener, the dorsal
groove is absent. Furthermore, its back has a gray-brown cape, the
sides are lighter and the belly is whitish. However, this colour
pattern can be much brighter, almost white on the sides and light
grey / ebony on the back. The head of the snubfin dolphin is blunt,
round and bulbous and there is no beak. The line of the mouth is
straight, and there is a distinct neck crease. Its dorsal fin is
small and rounded and set somewhat behind mid-back. The large flippers
have curved leading edges and their tips are rounded. Adult size
reaches 2.3 m in females and 2.7 m in males, and body mass reaches
130 kg (Robertson and Arnold, 2009).
This species was previously considered as a sub-population of the
Irrawaddy dolphin. However, clear and consistent differences in
coloration, morphology and genetics are consistent with species-level
differences (Beasley et al. 2005).
Snubfin dolphins are discontinuously distributed mostly in the
coastal, shallow, brackish, or fresh turbid waters at the mouths
of rivers. The species occurs in northwestern New Guinea; southern
New Guinea from the coast of Merauke east to the Gulf of Papua,
thence south to northern Australia where it ranges from Broome in
Western Australia around to the Brisbane River in Queensland. The
snubfin dolpfin occurs on the Sahul shelf of Australia and Papua
New Guinea and is separated from the Irrawaddy dolphin (Sunda shelf
of South and Southeast Asia) by the deep oceanic waters between
(Robertson and Arnold, 2009).
Distribution of Orcaella heinsohni: warm coastal
waters and rivers in Northern Australia;
Papua New Guinea and Indonesia (Reeves et al. 2008 © IUCN;
3. Population size
Very little is known about the population size of this species
(Reeves et al. 2008; Robertson and Arnold, 2009). Standard aerial
survey techniques were used to survey coastal waters adjacent to
the Northern Territory, Australia. Relatively few snubfin dolphins
were observed in waters off the north-west coast. Substantial populations
were located in the western Gulf of Carpentaria yielding a total
estimate of approximately 1,000 individuals on the surface. The
major concentration was located in Blue Mud Bay (Freeland and Bayliss,
1989). This is the largest population known in Australia (Reeves
et al. 2008), however, these data are now more than 20 years old
and requires confirmation.
More recent abundance estimates were made by Parra et al. (2006b)
who used photo-identification data collected between 1999 and 2002
in Cleveland Bay, northeast Queensland to estimate an abundance
of 76 (CV = 0.08) individuals in 2000, 64 (CV = 0.11) in 2001 and
67 (CV = =0.14) in 2002. Due to low sample size and high CV, the
authors estimated that it wouldl take six years to detect a population
change of 5% p.a., and two years to detect a 20% p.a. change. Parra
et al. (2006b) estimated that population estimates at a regional
level are likely to be in the order of thousands rather than tens
of thousands; during aerial surveys covering most of the east Queensland
Coast between 1987 and 1995, only 29 sightings of snubfin dolphins
were recorded (Corkeron et al., 1997; Parra et al., 2002) and during
boat-based line transect surveys in selected areas of northeast
Queensland there were only 22 sightings (Parra, 2005).
4. Biology and Behaviour
Habitat: In Australian waters, snubfin dolphins appear to
avoid waters less than 2.5 m and greater than 18 m deep (Freeland
and Bayliss 1989). Preference for nearshore, estuarine waters is
likely related to the productivity of these tropical coastal areas
(Parra et al. 2006a). Off Cleveland Bay there is evidence that animals
occur mainly in waters close to the coast. Most sightings of snubfin
dolphins made during aerial surveys (Corkeron et al., 1997; Parra
et al., 2002) and boat-based line transect surveys including offshore
waters (waters >10 km from the coast) of different areas along
the Queensland coast, occurred in waters within 6 km of the nearest
coastline. In summary, shallow coastal areas adjacent to river and
creek mouths and sea grass beds form the preferred habitat. Surfacing
is inconspicuous, with a low roll showing very little of the back
and small dorsal fin. Therefore the species is easily missed in
the field (Robertson and Arnold, 2009).
Schooling: Mean group size was 5.6 (Parra and Corkeron in
IWC, 2000); group sizes of up to 14 animals have been observed (Parra
et al. 2002). The species is observed to co-occur with the Indo-Pacific
humpback dolphin, towards which it shows aggressive and sexual behaviour
(Robertson and Arnold, 2009).
Food: Snubfin dolphins appear to be opportunistic-generalist
feeders, eating a wide variety of fish and cephalopods associated
with coastal-estuarine waters. Bottom-dwelling and pelagic fishes
are consumed, indicating snubfin dolphins capture fish throughout
the water column. The most important prey in numerical terms for
snubfin dolphins was the cardinal fish (Apogon sp.), followed
by the cuttlefish (Sepia sp.), the squid Uroteuthis
(Photololigo) sp. and the toothpony fish (Gazza sp.)
(Parra and Jedensjö, 2009)
Reproduction: The calving season is not well known. Gestation
may last approximately 14 months. Maturity seems to be reached at
4-6 years of age and longevity is around 30 years (Robertson and
Freeland and Bayliss (1989) reported significant seasonal changes
in distribution. Parra and Corkeron (in IWC, 2000) found that all
animals identified during 1998 in Cleveland and Bowling Green Bays
in Northern Queensland, Australia, were resighted in 1999, suggesting
some degree of residency. More recently, Parra et al. (2006b) found
that 68% of the snubfin dolphins photo-identified in Cleveland Bay
were identified in more than one calendar year.
Incidental catch: Snubfin dolphins are accidentally caught
in fishing nets and in anti-shark nets in Australia (IWC, 2000).
They occurr close to river mouths; drowning in nearshore gillnets
set across creeks, rivers, and shallow estuaries represents one
of the major threats to nearshore dolphins along the Queensland
coast (Parra et al. 2006a).
Habitat degradation: Habitat degradation is seen as an important
conservation concern (Parra et al. 2006a; Robertson and Arnold,
2009). According to Hale (1997) the habitats in Australia include
estuaries and near-shore coastal areas which are utilised for resource
extraction and recreation and have been degraded in many areas as
a result of urban, industrial and agricultural development. Conservation
problems include loss of prey from over-fishing and destruction
of fish habitat, vessel disturbance, possibly pollution and maybe
directed killing. Long-term conservation will require a mixture
of regulation, education and community involvement.
Range states (Reeves et al. 2008) : Australia; Indonesia;
Papua New Guinea
O. heinsohni is listed in appendix II of CMS. The species
is also listed in Appendix II of CITES.
IUCN categorises O. heinsohni as "Near Threatened".
It is assumed that there are fewer than 10,000 mature individuals,
that the range is limited, that densities in surveyed areas are
low and that vulnerability, especially due to by-catch, is high.
Reassessment of the species requires more extensive surveys and
the outcome may be to classify the species as Vulnerable or even
Endangered (Reeves et al. 2008).
In its report on small cetaceans (IWC, 2000) the IWC Scientific
Committee's sub-committee on small cetaceans recommended that comprehensive
surveys be conducted to assess abundance, distribution, and habitat
quality and that a review be carried out of the distribution and
habitat preferences in marine systems and to define oceanographic,
bathymetric and biological features associated with high density
areas, The sub-committee expressed concern about increases in fishing
effort, particularly with gillnets, in some parts of the range of
this species. Given the apparently small size of some populations,
some by-catches in these fisheries may be unsustainable. The sub-committee
recommended that appropriate by-catch mitigation strategies be developed
for use with this species (IWC, 2000). See also general recommendations
on small cetaceans in Southeast Asia iterated in Perrin
et al. (1996).
· Beasley I, Roberston KM, Arnold P (2005) Description of
a new dolphin, the Australian snubfin dolphin Orcaella heinsohni
sp. n. (Cetacea, Delphinidae). Mar Mamm Sci 21: 365-400.
· Corkeron PJ, Morissette NM, Porter LJ, Marsh H (1997) Distribution
and status of hump-backed dolphins, Sousa chinensis, in Australian
waters. Asian Marine Biology 14, 49-59.
· Freeland WJ, Bayliss P (1989) The Irrawaddy River dolphin
(Orcaella brevirostris) in coastal waters of the Northern
Territory, Australia: Distribution, abundance and seasonal changes.
Mammalia 53: 49-58.
· Hale P (1997) Conservation of inshore dolphins in Australia.
Asian Mar Biol 14: 83-91.
· IWC (2000) Annex K: Report of the sub-committee on small
cetaceans. Rep Int Whal Comm, Cambridge, UK.
· Parra, G.J., 2005. Behavioural ecology of Irrawaddy, Orcaella
brevirostris (Owen in Gray, 1866), and Indo-Pacific humpback
dolphins, Sousa chinensis (Osbeck, 1765), in northeast Queensland,
Australia: a comparative study. Ph.D. Thesis, James Cook University,
· Parra GJ, Azuma C, Preen AR, Corkeron PJ, Marsh H (2002)
Distribution of Irrawaddy dolphins, Orcaella brevirostris,
in Australian waters. Raffles Bulletin of Zoology Supplement 10,
· Parra GJ, Schick R, Corkeron PJ (2006a) Spatial distribution
and environmental correlates of Autralian snubfin and Indo-Pacific
humpback dolphins. Ecography 29: 396-406
· Parra GJ, Corkeron PJ, Marsh H (2006b) Population sizes,
site fildelity and residence patterns of Australian snubfin and
Indo-Pacific humpback dolphins: Implications for conservation. Biol
Conserv 129: 167-180
· Parra GJ, Jedensjö M (2009) Feeding habits of Australian
Snubfin (Orcaella heinsohni) and Indo-Pacific humpback dolphins
(Sousa chinensis). Project Report to the Great Barrier Reef
Marine Park Authority, Townsville and Reef & Rainforest Research
Centre Limited, Cairns (22pp.).
· Perrin WF, Dolar MLL, Alava MNR (1996) Report of the Workshop
on the Biology and Conservation of Small Cetaceans and Dugongs of
Southeast Asia. East Asia Seas Action Plan. UNEP(W)/EAS WG. 1/2,
Bangkok, Thailand, 101 pp.
· Reeves RR, Dalebout ML, Jefferson TA, Karczmarski L, Laidre
K, O'Corry-Crowe G, Rojas-Bracho L, Secchi ER, Slooten E, Smith
BD, Wang JY, Zhou K (2008) Orcaella heinsohni. In: IUCN 2009.
IUCN Red List of Threatened Species. Version 2009.2. <www.iucnredlist.org>.
· Robertson KM, Arnold PW (2009) Australian snubfin dolphin
Orcaella heinsohni. In: Encyclopedia of marine mammals (Perrin
WF, Würsig B, Thewissen JGM, eds.) Academic Press, Amsterdam,
© Boris Culik (2010) Odontocetes. The
toothed whales: "Orcaella heinsohni". UNEP/CMS
Secretariat, Bonn, Germany.http://www.cms.int/small-cetaceans
© Illustrations by Maurizio Würtz, Artescienza.
© Maps by IUCN.