After 17 years of painstaking research, scientists have classified the Australian humpback dolphin (Sousa sahulensis) as a fourth species of humpback dolphin.

Native to the Sahul Shelf in the waters off northern Australia, S. sahulensis likely evolved independently from other closely related species due to zoogeographical barriers such as the Wallace Line (see “Kissing Cousins”). An argument among researchers for decades, the Wallace Line — which is a recognized dividing boundary for terrestrial species — is also a barrier for marine species.

“‘[It took] ‘detective work’ going through [century-old] papers, and matching bones. Genetic analyses provided the firm answer,” said Thomas Jefferson, co-author of the taxonomic paper on the dolphins.

Australian humpback dolphins aren’t colored the pink-tinged white of their closest relative, Sousa chinensis, found off Western Australia. They’re dark gray and have a distinctive dark dorsal “cape.” More important, the new classification could help with their conservation since present siting data estimates that there are only a few thousand individuals.

“The new taxonomy should emphasize the need,” Jefferson said. “A new IUCN Red List assessment will likely be done in the next year in collaboration with our Australian colleagues.”

Three other species closely related to Sousa sahulensis:

Atlantic humpback dolphin (Sousa teuszii) - West African coast

Indo-Pacific humpback dolphin (Sousa chinensis) - Western Australia

Indian Ocean humpback dolphin (Sousa plumbea) - Coastal waters of the Indian and Pacific oceans from northern Australia and southern China in the east, through Indonesia, and around the coastal rim of the Indian Ocean to southern Africa.

The 411 on Humpback Dolphins — From the World Wildlife Fund

• The snouts of Indo-Pacific dolphins in Australian waters actually whiten with age, making them look sun-kissed with freckles.
• Coastal dolphins are among the most threatened of all the world’s cetaceans because they inhabit the most heavily fished, polluted and developed environments.
• Humpback dolphins prefer shallower waters, and even wander into coastal mangroves. Designing proper marine protected areas to conserve as much of their critical habitat areas as possible would help protect the species.