Australian humpback dolphin
Common name: Australian humpback dolphin
Scientific name: Sousa sahulensis
Conservation status: The Australian humpback dolphin is listed as Vulnerable in Queensland (Nature Conservation Act 1992). It is ranked as a critical priority under the department's Back on Track species prioritisation framework. Local populations are considered to be vulnerable to decline because of small population sizes and low population growth rates.
The Australian humpback dolphin (Sousa sahulensis) was described as separate species in 2014. Australian humpback dolphins lack the hump present in other species of Sousa and their dorsal fin is low and triangular. Newborn calves are about 1 m in length and grow to around 2.7m and up to 280kg in weight Australian humpback dolphins are mostly grey with a lighter belly, separated by a diagonal ‘cape’ with indistinct margins. Young calves are darker than adults, and the beak, forehead and dorsal fin whiten with age. The beak is long and cylindrical, containing about 31 to 33 teeth in each row. The tail is large and the flippers are short and rounded. A hybrid between an Australian humpback dolphin and an Australian snubfin dolphin (Orcaella heinsohni) was recently discovered in Western Australia, but hybrids are considered to be rare.
Habitat and distribution
Australian humpback dolphins are found in coastal waters of northern Australia, with resident populations from Moreton Bay in Queensland to Shark Bay, Western Australia. They are also found in southern waters of New Guinea. Australian humpback dolphins are referred to as an 'inshore' species because they mostly occur in shallow nearshore waters, often at the mouths of estuaries and in tidal channels. Although humpback dolphins have been recorded up to 55km offshore on the northern Great Barrier Reef, they are primarily found within 20km of the coast. Key localities in Queensland include Moreton Bay, the Great Sandy Strait, Port Curtis, Port Alma-Keppel Bay, Shoalwater Bay, Mackay-Whitsundays, Townsville-Hinchinbrook and Bathurst Bay. The distribution of Australian humpback dolphins is poorly known in the Gulf of Carpentaria and the Cape York Peninsula, but they have been reported in waters off Weipa, Mapoon and Mornington Island.
Life history and behaviour
Australian humpback dolphins occur in groups of up to 31, but are mostly seen in smaller groups of 2–4 individuals They are thought to have a ‘fission-fusion’ society with mostly short-term social bonds, aside from strong associations between mothers and their calves which can last for up to four years. They are considered to be opportunistic feeders, eating mostly fish associated with estuarine and inshore waters. Humpback dolphins often chase prey in shallow water and are sometimes observed to strand feed, where they beach themselves deliberately in order to catch fish. They have also been recorded feeding in association with prawn trawlers. Unlike bottlenose dolphins, Australian humpback dolphins do not bow ride but they often leap clear from the water.
There have been no detailed studies on the life history of this species, what is known of the reproductive biology of humpback dolphins comes from the Chinese white dolphin, Sousa chinensis and the Indian humpback dolphin, Sousa plumbea. This suggests that sexual maturity is attained at 14–17 years, gestation lasts 10–12 months and the interval between calving is 3–4 years. Not much is known about the longevity of Australian humpback dolphins, but a dolphin called Amity was caught as a young adult in 1968 and still lives at Sea World, suggesting that they can live for over 51 years.
Threats to the Australian humpback dolphin include habitat loss and degradation from development, poor water quality, noise pollution, boating activities, unregulated feeding, incidental capture in fisheries and incidental capture by the Shark Control Program. Entanglement and ingestion of recreational fishing gear (hooks and line) or marine debris may also pose a threat. Humpback dolphins are exposed to pollution that is amplified up the food chain, and may cause them to be more susceptible to disease.
- Implement sustainable fisheries management to ensure adequate stocks of the dolphin's prey and to minimise incidental capture in nets.
- Improve water quality on the Great Barrier Reef through the Reef Water Quality Protection Plan.
- Protect significant Australian humpback dolphin habitat through marine parks.
- Promote fishing practices that reduce interactions with wild dolphins.
- Provide education on the impacts of boating activities and unregulated feeding.
- Undertake ongoing research and monitoring to determine more about the species' life history parameters, distribution, movement patterns and population sizes.
- Monitor dolphin mortality along the Queensland coast via StrandNet, the marine wildlife stranding and mortality database.
What can you do to help this species?
- Report injured, sick, entangled, stranded or dead dolphins to the RSPCA hotline on 1300 ANIMAL (1300 264 625).
- Do not approach too closely with your boat as species as Australian humpback dolphins are sensitive to harassment and unfamiliar noise, and boats may directly injure them or disturb their natural behaviour.
- Avoid fishing near dolphins that are feeding – they may mistake your bait for food; avoid feeding dolphins with leftover bait and use corrodible hooks.
- Do not feed wild dolphins. Special management provisions are in place for feeding a small number of wild humpback dolphins in Tin Can Bay. Unregulated feeding of wild dolphins can introduce disease and cause behavioural changes (such as dolphins learning to approach fishers or boats).
- Remember that rubbish you throw away, or chemicals you discard, may find their way into drainage systems that run into the ocean. Such pollutants can affect the health of coastal mammals directly, or indirectly through accumulation of poisonous substances in their prey.
- Do not dump your pet cat's waste into drains. Cat faeces can contain the parasite Toxoplasmosis gondii which has caused the death of inshore dolphins.
Bannister, JL, Kemper, CM and Warneke, RM 1996, The Action Plan for Australian Cetaceans, Wildlife Australia Endangered Species Program Project Number 380.
Brown, A.M., Kopps, A.M., Allen, S.J., Bejder, L., Littleford-Colquhoun, B., Parra, G.J., Cagnazzi, D., Thiele, D., Palmer, C. and Frere, C.H. (2014) Population differentiation and hybridisation of Australian snubfin (Orcaella heinsohni) and Indo-Pacific humpback (Sousa chinensis) dolphins in north-western Australia. PLoS ONE 9, e101427.
Jefferson TA, Rosenbaum HC 2014. Taxonomic revision of the humpback dolphins (Sousa spp.), and description of a new species from Australia. Marine Mammal Science 30:1494-
Meager J.J. and Limpus, C. (2014) Mortality of inshore marine mammals in eastern Australia is predicted by freshwater discharge and air temperature. PLoS ONE 9, e94849.
Parra, G.J. and Cagnazzi, D. (2015) Conservation status of the Australian humpback dolphin (Sousa sahulensis) using the IUCN Red List Criteria. Advances in Marine Biology 73, 157–192.
Weijs, L., Vijayasarathy, S., Villa, C.A., Neugebauer, F., Meager, J.J. and Gaus, C. (2016) Screening of organic and metal contaminants in Australian humpback dolphins (Sousa sahulensis) inhabiting an urbanised embayment. Chemosphere 151, 253–262.