Genetic study reveals vulnerability of north-west dolphins

July 3, 2014

There are little-known dolphins inhabiting Western Australia’s north coast, and a new study has highlighted the vulnerability of local populations.

Australian snubfin (Orcaella heinsohni) and humpback dolphins (Sousa sp.) occur throughout tropical coastal waters of northern Australia, but little is known of their abundance or life history characteristics because much of their range is remote from human population centres.

Researchers from Murdoch University’s Cetacean Research Unit have worked with a number of collaborators to produce the first estimates of population genetic structure of two coastal dolphin species of north-western Australia.

The study, led by Murdoch PhD student Alex Brown and Dr. Anna Kopps (University of Groningen, Netherlands) and funded by the Australian Marine Mammal Centre, was published in the international journal PLOS ONE this week.

“Both snubfin and humpback dolphins are listed as ‘near threatened’ by the IUCN, but the lack of information about them has prevented a comprehensive assessment of their conservation status,” Alex said. “The few studies conducted to date suggest that they occur in small populations that are dependent on the coastal environment and are, therefore, sensitive to coastal habitat modification.”

“Large-scale industrial development is occurring across north-western Australia, resulting in modification to coastal habitats through dredging, construction and increased shipping.

“With so little data on coastal dolphins in this region, the potential impact of these developments remains unknown.

“We set out to establish whether these species represent large, genetically mixed populations or a collection of smaller, isolated populations,” explained Alex. “Gaining an understanding of these species’ population structure is crucial to assessing their vulnerability to a changing environment and informing management agencies in order to apply appropriate conservation measures.

Using small tissue samples collected with a dart, the researchers compared the genetic characteristics of 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.

“Results showed that there wasn’t much mixing between the populations,” Alex said. “They are fairly isolated, with low levels of gene flow between populations separated by about 300 km of coastline”.

“Existing as a series of small populations with limited gene flow, they are more vulnerable to environmental change and localised extinctions compared to a single, larger population,” explained senior author Dr Celine Frère of the University of the Sunshine Coast.

The researchers are urging management agencies to treat the dolphin populations as small, discrete fragments and to preserve corridors for individuals to travel between populations.

In another first, Alex documented the first recorded hybrid between a humpback and snubfin dolphin.

“We were at first puzzled by this unusual looking dolphin,” said Alex.

“At first glance it resembles a humpback dolphin, but a closer look reveals a small beak – shorter than a humpback or bottlenose dolphin, but very different from the rounded, porpoise-like head of a snubfin,” he described.

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

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

The full open access article is available at the PLOS ONE website.

Further information about the study and coastal dolphins in the north-west of Australia is available here.

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