Inshore tropical dolphin under pressure to survive

The discovery of new information about the limited population genetics of Australia’s most endangered dolphin, the Australian humpback dolphin, has been published in Biological Conservation

The research is based on genetic studies spanning a decade and shows that the endangered native species has a very low genetic diversity and gene flow.

“Our results show that Australian humpback dolphin populations along the east coast of Queensland are characterised by low levels of genetic diversity, limited gene flow, and small effective population size,” says research project leader Dr Guido Parra from Flinders University. Dr Parra leads the Cetacean Ecology, Behaviour and Evolution Laboratory (CEBEL) conservation and ecology centre at Flinders.

“Conservation efforts should focus on promoting connectivity among local populations and reducing direct causes of human related mortality. Our study has provided critical insights into their genetic population structure and demographic history that is essential for their conservation.”

Australian humpback dolphins (Sousa sahulensis) were recently described as a new species, and are endemic to coastal waters of northern Australia and southern New Guinea. They occur in small numbers and are considered Vulnerable under the International Union for Conservation of Nature (IUCN) Red List of threatened species.

Dr Daniele Cagnazzi, from the Marine Ecology Research Centre at Southern Cross University, is one of the assessors for the revised conservation status of Australian humpback dolphins under the IUCN.

He said the results of the study should “raise important conservation concerns and emphasise the vulnerability of this species to random natural and human disturbances”.

“Understanding the population genetics of threatened species is imperative for the development of appropriate conservation measures because some may be more vulnerable to natural and human disturbances than others depending on their genetic diversity and past demographic history."

Dr Cagnazzi said the project was possible thanks to the collaboration of many researchers around Australia.

"When Dr Guido Parra and myself first started collecting skin samples from Australian humpback and snubfin dolphins, it was considered an impossible task. Certainly it proved to be a major challenge which required substantial efforts from everyone involved. I am very pleased to see such hard work resulted in important outcomes for the conservation of humpback in Australia."

Finding Australian humpback dolphins in the wild is not an easy task given their low population sizes, high mobility and their inconspicuous nature. Thus, the genetic samples were collected over the past 10 years by researchers including Dr Parra and Dr Cagnazzi.

The demographic history shows signs of historical population bottlenecks and/or founder events during the late Holocene period (~1250–3750 years ago), probably associated with sea level fall and increased intensity of El Niño Southern Oscillation-climatic events.

The study was possible through funds by the the Sea World Research and Rescue Foundation,  Ocean Park Conservation Foundation, the Australian Marine Mammal Centre, Fitzroy River Basin Association, Burnett Mary Regional Group, and Queensland Parks and Wildlife Service.

The research concludes that the low effective population sizes of humpback dolphins indicate that the death of even a few mature individuals per year, for example in inshore gillnets,  shark nets or other fishing, boating or industrial activity, could have detrimental consequences on the viability of local populations.

Researchers say conservation efforts need to continue to focus on reducing direct causes of human-related mortality on humpback dolphins to prevent extinction.

Article written in conjunction with Flinders University.

‘Low genetic diversity, limited gene flow and widespread genetic bottleneck effects in a threatened dolphin species, the Australian humpback dolphin,’ by GJ Parra, D Cagnazzi, M Jedensjo, C Ackermann, C Frere, J Seddon, N Nikolic and M Krutzen, has been published in Biological Conversation (Elsevier).