A newly discovered species of dolphin has been found swimming off the northern Australian coast.

Scientists say the as yet unnamed dolphin is part of the humpback family, which already contains three other species.

The Atlantic humpback (Sousa teuzii) is found in the eastern Atlantic off western Africa, while there are two other Indo-Pacific humpbacks: the Sousa plumbea, found in the central to western Indian Ocean, and the Sousa chinensis, seen in the eastern Indian and western Pacific oceans.

Scientists say the new species is part of the Indo-Pacific variety.

They reached their conclusion after examining 180 skulls and 235 tissue samples from other humpback dolphins and analysing the DNA for variations, the Wildlife Conservation Society (WCS) said.

"Based on the findings of our combined morphological and genetic analyses, we can suggest that the humpback dolphin genus includes at least four member species," Martin Mendez of the WCS said in a statement.

"This discovery helps our understanding of the evolutionary history of this group and informs conservation policies to help safeguard each of the species."

Humpback dolphins, named for a hump below their dorsal fin, grow up to 2.5 metres in length and their colouring ranges from dark grey to pink or even white, the WCS said.

"New information about distinct species across the entire range of humpback dolphins will increase the number of recognised species, and provides the needed scientific evidence for management decisions aimed at protecting their unique genetic diversity and associated important habitats," WCS Ocean Giants program director Howard Rosenbaum was reported as saying.

The findings have been published in the journal Molecular Ecology.

ABC/Reuters