Australian Humpback Dolphins
Species Name: Sousa sahulensis
Australian Humpback Dolphins have a lengthened, low and triangular dorsal fin and a humped back appearance. As the dolphins age, the fatty tissue causes the hump to increase and the colouring of the forehead and dorsal fin to whiten. Calves are born grey and are often 1 metre in length and can grow up to 2.7 metres.
Humpback dolphins have mounded foreheads and long beaks containing around 31 to 33 teeth. The flippers of these species are short and rounded with a large tail.
These dolphins grow between 2.6-2.7 metres. These dolphins can weigh up to between 260kg, but commonly weigh around 200kg.
Biology and Ecology
Australian Humpback Dolphins can be found commonly in the tropical waters of Northern Australia such as Moreton Bay and Gladstone, as well as Southern New Guinea. They can also be found in the tropical waters of Shark Bay, Western Australia. They prefer regions where waters are less than 20 metres deep, estuarine and coastal regions.
This species prefers a diet of fish, prawns, molluscs, crabs, squids and octopus depending on the season. They are described to be opportunistic feeders. Australian Humpback Dolphins reach sexual maturity around the age of 14. Gestation lasts between 10-12 months.
Behaviour and Social Organisation
They often hang around in groups of 31, but in Moreton Bay it has been recorded that group size is usually 2-3. They have strong mother and calf relationships, lasting up to four years.
Alpha males or sometimes alpha females lead the pod. They are leisurely swimmers and does not surf bow waves.
There is not much known about the communication of the Australian Humpback Dolphin. According to research conducted by S.M Van Parijs and P.J Corkeron at Moreton Bay found that Australian Humpback Dolphins increased the rate of whistling after the boat moved through the area less than 1.5km away, however this did not affect the rate of which dolphins produced click trains and burst pulse vocalisations, calves created fewer vocalisations. This suggests that the noise from the vessels affects group consistency. The research also suggests that mother and calf pairs exhibit a need to re-establish vocal connection.
The Australian Humpback Dolphin is listed as vulnerable in Queensland (Nature Conservation Act 1992 (Queensland): August 2015 list as Sousa sahulensis) due to habitat destruction which has been caused by development, tourism, and incidental capture from shark control programs and fisheries.
The Australian Humpback Dolphin is also listed as vulnerable under the IUCN Red List.