It’s official: Australia has its own species of humpback dolphin, Sousa sahulensis.
Humpback dolphins of the genus Sousa are found along the coasts of Africa, Asia and Australia. Scientists had originally divvied them up into three species. One swam on the west coast of Africa. The second inhabited the east coast and the waters of the Middle East and India. And the third stretched from the northeast coast of India into the rest of the coastal areas of Asia and northern Australia.
But researchers have been gathering evidence for years that the third group was really two species. Last year, for instance, Science News reported that scientists had used DNA sequencing and skull morphology to identify the Australian animals as a distinct species.
A species doesn’t become official, however, until it gets a name, which happened with a July 31 report in Marine Mammal Science. Thomas Jefferson of Clymene Enterprises in Lakeside, Calif., and Howard C. Rosenbaum of the Wildlife Conservation Society in New York City examined and reviewed all the Sousa dolphins, naming the new species S. sahulensis, after the Sahul Shelf, which sits between Australia and New Guinea.
That shelf turns out to be important in explaining why S. sahulensis is separate from the species to the north, S. chinensis. The waters on the shelf are shallow, perfect for humpback dolphins. But then the ocean gets deep and the animals can’t cross.
That’s actually a problem for lots of animals, both terrestrial and marine. Scientists have recognized the barrier created by this deep region and named it Wallace’s Line, after naturalist Alfred Russel Wallace. The ancestor of today’s humpback dolphins would only have been able to cross that line long in the past when the oceans were much shallower than today. When sea levels rose, the Australian population was cut off and evolved into a separate species.
The Australian humpbacks have a similar shape to S. chinensis, but they have fewer teeth and different coloring. Instead of pinky white, these dolphins are dark gray, sometimes with white spots.
Their conservation status is unknown, but it’s unlikely that there are more than a few thousand of these dolphins overall, the researchers say.
“Australian humpback dolphins throughout their range are threatened by coastal zone development, fisheries interactions, vessel impacts and pollution,” notes Guido Parra, who studies dolphins at Flinders University in Adelaide, Australia. One big worry for the Australian humpbacks is the development of port facilities for oil, gas and mining operations in northwest Australia, which could degrade or destroy habitat for a small and vulnerable population of the animals.
But the first step to conserving the new species has already been taken. “Successful wildlife conservation and management requires baseline information on species identity and distribution,” says Parra. After all, it’s pretty difficult to save something if you don’t know anything about it.