Australian humpback dolphin
Australian humpback dolphin (Fitzroy River, Qld). Photo: Susan Crocetti
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 of Environment and Heritage Protection 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 recently described as a separate species. Australian humpbacks lack the hump present in other species of Sousa and their dorsal fin is low and triangular. Newborn calves are about 1m in length and grow to around 2.7m. Australian humpbacks 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.
Habitat and distribution
Australian humpback dolphin (Moreton Bay, Queensland). Photo: EHP
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 the island 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, Gladstone, Port Clinton, Repulse Bay, Townsville-Hinchinbrook, Bathurst Bay, Weipa and Mornington Island.
Life history and behaviour
Australian humpback dolphins occur in groups of up to 31. In Moreton Bay, their reported average group size is 2 - 3. They are thought to be opportunistic feeders, eating mostly fish associated with estuarine and inshore waters. They have been recorded feeding in association with prawn trawlers. 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. Strong mother and calve associations may persist for up to 4 years.
Group of Australian humpback dolphins off Townsville, Queensland. Photo: EHP
Threats to the Australian humpback dolphin include habitat destruction and degradation from development, noise pollution, boating activities, illegal 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;
- Minimise the amount of pollutant and sediment output into coastal waters through appropriate catchment management;
- Provide education on the impacts of boating activities on the dolphin;
- Promote fishing practices that reduce interactions with wild dolphins;
- Undertake ongoing research and monitoring to determine more about the species' biological parameters, population size and trends, habitat requirements, and threats.
What can you do to help this species?
You can help this species by:
- not approaching too closely with your boat as species such as Australian humpback dolphins rarely ride the bows of boats and may be sensitive to harassment and unfamiliar noise, and boats may directly injure them or disturb their natural behaviour;
- remembering 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;
- not dumping your pet cat's waste into drains. Cat faeces can contain the parasite Toxoplasmosis gondii which has caused the death of inshore dolphins;
- avoid fishing near dolphins that are feeding – they may mistake your bait for food; avoid feeding dolphins with leftover bait and use corrodible hooks.
Baker, AN, 1983 Whales and dolphins of New Zealand and Australia, Victoria University Press, Wellington, New Zealand.
Bannister, JL, Kemper, CM and Warneke, RM 1996, The Action Plan for Australian Cetaceans, Wildlife Australia Endangered Species Program Project Number 380.
Jefferson TA, Rosenbaum HC 2014. Taxonomic revision of the humpback dolphins (Sousa spp.), and description of a new species from Australia. Marine Mammal Science 30:1494-1541.
Parra, GJ, Corkeron PJ and Marsh, H 2004, The Indo-Pacific humpback dolphin, Sousa chinensis, in Australian waters: a summary of current knowledge, Aquatic Mammals 30, 197-206.
Rice, DW 1998, Marine Mammals of the World: Systematics and Distribution, Special Publication Number 4, The Society for Marine Mammalogy, Lawrence, Kansas.