Australian snubfin dolphin
Adult Australian snubfin dolphin off Townsville. Photo: Guido Parra
Common name: Australian snubfin dolphin
Scientific name: Orcaella heinsohni
Legislative name: Orcaella brevirostris
Family: Delphinidae
Conservation status: The Australian snubfin dolphin is listed as Near Threatened in Queensland (Nature Conservation Act 1992). This dolphin was assumed to be the Irrawaddy River dolphin (Orcaella brevirostris) until 2005 when genetic tests proved that it was a separate species. It is currently only known from Australia and its status in Queensland waters is very poorly known. It is ranked as a critical priority under the Department of Environment and Resource Management Back on Track species prioritisation framework.
Description
The Australian snubfin dolphin is a relatively small cetacean (dolphin and whale family). Adults average 2 metres in length (maximum male - 2.75 m, maximum female - 2.32 m). It has a blunt, rounded head and no beak. There are 12-19 small, conical teeth on each side of both jaws. The blowhole is left of the midline. It has an obvious, flexible, neck, and neck creases may be present.
The flippers are large and broad, with a gently curved leading edge. The dorsal (back) fin is small and triangular with a bluntly rounded tip, and barely concave rear margin. It is situated behind the midpoint of the body. The flukes (tail fins) are notched and have a shallow concave trailing edge. The colour is generally pale to dark brown with the ventral (underside) surface lighter in colour. This species is often confused with the dugong, which lacks a dorsal fin and has a more full-bodied shape.
Habitat and distribution
The Australian snubfin dolphin has been recorded across northern Australia (Qld, NT, WA) where it inhabits riverine, estuarine and coastal waters, but the distribution has been poorly documented.
Life history and behaviour
The Australian snubfin dolphin is usually seen in groups of 5 to 6 animals, but groups of up to 15 animals have been observed. When undisturbed they typically make short dives, surfacing quietly at 30-60 sec intervals. They can submerge for up to 12 minutes when disturbed. Tail-slapping and partial jumps have been observed, but they do not leap clear of the water or bow-ride. Vocalisation (sounds/language) includes broadband clicks, pulsed sounds and whistles.
Social sexual activity in Australian snubfin dolphins is seen year round with a peak during the winter months. Calves are also seen year round but tend to peak in winter months.
The Australian snubfin dolphin is a generalist feeder, taking food from the bottom and the water column. Its diet consists primarily of fish, but includes cephalopods (such as squid and octopus) and crustaceans (such as prawns and crabs).
Threatening processes
Known threats to the Australian snubfin dolphin are incidental capture from netting, especially gill nets and the nets set as part of the Queensland Shark Control Program. Suspected threats in Queensland include prey depletion due to overfishing, inshore pollution and habitat destruction arising from coastal development. Noise, interference and collisions from boat and jet ski activity may also injure these dolphins or interfere with their natural behaviour.
Recovery actions
- Implement sustainable fisheries management to ensure adequate stocks of the dolphin's prey and to minimise accidental capture;
- Take steps to limit and eventually eliminate deaths due to netting;
- Minimise the amount of pollutants and sediment output into coastal waters through appropriate catchment management;
- Establish a baseline estimate of population size and conduct regular population monitoring throughout range to detect possible change in numbers;
- Conduct further research to establish life history parameters, habitat requirements, and level of genetic interchange between populations.
What can you do to help this species?
You can help this species by:
- not approaching dolphins too closely with your boat as species such as the Australian snubfin dolphin may be sensitive to harassment and unfamiliar noise, and boats may 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.
Last updated 7 December 2011