Two little-known Australian dolphin species are vulnerable to human coastal development and could be at risk of localised extinction, the first research to consider the population structure of the two species shows.

The Australian snubfin and humpback dolphins are found throughout the tropical waters of the WA north coast and are remote from human populations, making them difficult to study.

While both are listed as "near threatened" by the International Union for Conservation of Nature, a lack of information about them has prevented a comprehensive assessment of their conservation status.



Researchers from Australian and international universities collected small tissue samples with a dart from two populations of each species: snubfin dolphins from Roebuck Bay and Cygnet Bay in the Kimberley region and humpback dolphins from the North West Cape and the Dampier Archipelago in the Pilbara.



This allowed them to compare genetic characteristics between the groups.



The snubfin dolphin. Photograph: Jenny Smith/Murdoch University Photograph: Jenny Smith/Murdoch University

Lead researcher and marine scientist from the Cetacean Research Unit at Murdoch University, Alex Brown, said they found the species existed in small, isolated populations up to 300km apart with not much mixing between the groups, resulting in limited gene flow.



It meant they could be particularly susceptible to coastal modification by humans through dredging, construction and increased shipping because it further isolate the populations from each other.

It could also lead to some of the small groups becoming susceptible to localised extinction if they could not travel for breeding or to increase genetic diversity within groups, the researchers say.

They are urging management agencies to preserve corridors for travel between populations.



“We would urge management authorities to look at the research and think about it when assessing the environmental impact of projects and dredging,” he said.



“Although they may not find a lot of these dolphins in the immediate location of where there are plans to build a coastal development or port, they need to consider that the area may be an important migration route.”



Estimates state there are fewer than 10,000 mature individuals in each species.



The findings published on Thursday in the journal, PLOS ONE, also documented the first recorded hybrid between a humpback and snubfin dolphin.



Genetic analysis revealed it to be the female offspring of a snubfin dolphin mother and humpback dolphin father.



The humpback-snubfin dolphin hybrid. Photograph: Dominic Clarke/Murdoch University Photograph: Dominic Clarke/Murdoch University

“Snubfin and humpback dolphins are often found in the same locations and aggressive and sexual interactions have been recorded previously between the two species,” Brown said.

“This might be a result of living in small, isolated populations and a consequent lack of same-species breeding opportunities.

“It really highlights how little we know about these animals.”

The age of the hybrid dolphin and whether or not it is fertile was unknown, he said.