The Australian humpback dolphin (''Sousa sahulensis'') is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of humpback dolphin and the fourth recognized humpback dolphin species chronologically. The specific name ''sahulensis'' is derived from the

Sahul Shelf Geologically, the Sahul Shelf () is a part of the continental shelf of the Australian continent, lying off the northwest coast of mainland Australia. Etymology The name "Sahull" or "Sahoel" appeared on 17th century Dutch maps applied to a ...

, located between northern Australia and southern New Guinea, where the Australian humpback dolphins occur. The species was

scientifically described A species description is a formal description of a newly discovered species, usually in the form of a scientific paper. Its purpose is to give a clear description of a new species of organism and explain how it differs from species that have be ...

on 31 July 2014 in the journal ''

Marine Mammal Science ''Marine Mammal Science'' is a quarterly peer-reviewed scientific journal covering all topics about or related to marine mammals. It is published by Wiley-Blackwell on behalf of The Society for Marine Mammalogy. According to the ''Journal Citation ...

''. As of August 2014, there is no population estimate for the Australian humpback dolphin, but based on available sighting data it is put to "a few thousand".

Appearance

Australian humpback dolphins are slightly different from the other three humpback dolphin species in overall length, number of teeth, vertebrae and geographic distribution. The

dorsal fin A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through c ...

of the Australian humpback dolphin is lower and more wide-based than those of the Atlantic humpback dolphin and the Indian Ocean humpback dolphin, and its coloration is dark gray, while its closest humpback relative, the Chinese white dolphin, has distinctly white (often with a pink tinge) coloration. The Australian humpback dolphin also has a distinctive dark dorsal feature, resembling a cape. Known size for Australian humpback dolphins range from 31/2 – 9 ft (1-2.7m). The dorsal fin is short, triangular in shape, and lacks the dorsal “Hump” typical of Atlantic and Indian humpback dolphins. The body is mainly dark gray in color, with flanks shading to the light gray. A diagonal cape line extending from just above the eye and neck down to the urogenital area separates the dark back and lighter belly. White scarring and dark flecking on the head, back, dorsal fin, and tail stock are common in adult animals. Birth weight is between 88-110 lb (40–50 kg) and adult weight is between 507-550 lb (230–250 kg).Berta, Annalisa, editor. Whales, Dolphins & Porpoises: A Natural History and Species Guide. University of Chicago Press, 2015.

Life history

Mating and calving occurs year-round. The gestation period lasts 10–12 months, lactation may last more than 2 years and a 3-year calving interval is likely. Individuals may live for at least 30 years. Scientists studied the dolphins for 17 years before finally coming to the conclusion that ''S. sahulensis'' was a separate species within the ''Sousa'' genus. It was DNA that proved most useful to determining its classification. Genetic analyses found 7 unique mitochondrial DNA bases and a single nuclear DNA base supporting it status as a new species.

Food and foraging

These dolphins are known to be opportunistic, generalist feeders, eating a wide variety of coastal-estuarine and inshore reef fish. Feeding may occur in a variety of habitats (mangroves, sandy-bottom estuaries,

seagrass meadow A seagrass meadow or seagrass bed is an underwater ecosystem formed by seagrasses. Seagrasses are marine (saltwater) plants found in shallow coastal waters and in the brackish waters of estuaries. Seagrasses are flowering plants with stems and ...

s, and inshore coral reefs) and involve animals dispersed over wide areas or tight groups targeting localized prey. These marine mammals are occasionally seen chasing fish into shallows and beaching themselves to catch their prey.

Conservation and management

There is no global population estimate but subpopulation estimates are in the low hundreds. Due to their coastal distribution, Australian humpback dolphins are vulnerable to a variety of threats including incidental captures in gill nets and shark nets set for bather protection, habitat loss and degradation, vessel strikes, pollution, and climate change. With an official species name, the new Aussie dolphin will have a greater chance of receiving special conservation treatment.

Behaviour

Australian humpback dolphins have been observed strand-feeding. They are generally shy and elusive and tend to keep their distance from boats. Humpback dolphins have been observed to display mating courtship between

Australian snubfin dolphin The Australian snubfin dolphin (''Orcaella heinsohni'') is a dolphin found off the northern coasts of Australia. It closely resembles the Irrawaddy dolphin (of the same genus, ''Orcaella'') and was not described as a separate species until 2005 ...

s.Annalisa Berta, 2015
Whales, Dolphins, and Porpoises - A Natural History and Species Guide

References

External links

{{Taxonbar, from=Q17476198 Australian humpback dolphin Cetaceans of the Pacific Ocean Marine fauna of Oceania Mammals of Papua New Guinea Fauna of the Northern Territory Australian humpback dolphin