By Dr Alex Brown

WAMSI-supported researchers have been in the Cambridge Gulf and Prince Regent River working with local rangers to find out more about the distribution, abundance and population structure of the Australian snubfin (Orcaella heinsohni) and humpback (Sousa sahulensis) dolphins.

The Australian snubfin and humpback dolphins are found in coastal and estuarine waters across northern Australia and the aim of the Kimberley Marine Research Program’s dolphin project is to contribute data towards assessment of their conservation status.

The first trip saw researchers Dr. Alex Brown (Murdoch University Cetacean Research Unit) and Dr. Simon Allen collaborate with the Balanggarra Rangers to perform a two-week survey in the Cambridge Gulf and adjacent coastal waters.

The aims were to:

1. collect data on the relative abundance and genetic connectivity of coastal dolphins; and
2. provide rangers with camera equipment and training in dolphin survey techniques – part of a project funded by the Commonwealth Government and WWF-Australia to support the capacity of Indigenous rangers across northern Australia to conduct dolphin research and monitoring.

Following a day of training presentations and exercises, the research team established a base camp at Lacrosse Island, 85 km north of Wyndham, providing good access to the remote waters at the top of the Cambridge Gulf. The support of Department of Parks and Wildlife’s utility vessel Joowinyin was essential to move food, fuel and equipment to the island.

A view of Turtle Bay and our camp from ‘Telstra Hill’. (Photo Alex Brown)

 

Using the ranger boat, the team covered a 476 km area, focusing on the northwest of the Gulf between the Lynne and Helby Rivers but also covering the open coast west to the Berkeley River, north along King Shoal and Medusa Bank, and east around Cape Domett.

Balanggarra Rangers, Wesley (left) and Wayne (centre left), assist with photo-identification alongside researcher Simon Allen (right) and skipper Andy Yardley (centre right). (Photo: Alex Brown)

 

Both species were encountered throughout the area surveyed, including the river mouth habitats, which they are known to often frequent, but also along less sheltered sections of open coast and where shallow waters extended further offshore.

Snubfin dolphins were sighted 22 times, while 18 schools of humpback dolphins were observed – providing ample opportunities for the Balanggarra Rangers to develop their data collection skills.

The survey team attempted to quantify the number of dolphins in the area by taking photographs of unique markings on their dorsal fins. However, many of the animals were too shy to be approached close enough for high-quality photos (< 50 m), and only one quarter of all dolphins approached could be properly recorded.

The boat-shy behaviour, which is not uncommon in these species, also limited the team’s success in using a darting system to obtaining tissue samples for genetic analyses – a single humpback dolphin sample being the total from the trip.

Snubfin dolphins (Photo: Pete O’Connor, Dambimangari Rangers)

 

On the second trip, Dr. Brown joined Parks and Wildlife and Dambimangari Rangers on PV Worndoom for an eight-day survey in Lalang-garram / Camden Sound Marine Park, focussing on the popular Prince Regent River.

Regular sightings of snubfin and humpback dolphins suggest this to be an important habit for these species – both of which are key indicators of marine park health under the management plan.

Photo-identification techniques were more successful in this area, and biopsy darting provided an additional two snubfin dolphin genetic samples.

With this initial survey complete, an ongoing monitoring program will be developed to allow park managers to monitor the status of tropical dolphin species in key parts of the park.

Overall, these data add to our understanding of the distribution and relative abundance of tropical inshore dolphins off northwest Australia, and provide comparisons to encounter rates at other studied sites in the western Kimberley.

The genetic samples will be analysed alongside others from the region, providing a starting point for further data collection and investigations of population connectivity in the Kimberley.

 

The $30 million Kimberley Marine Research Program is funded through major investment supported by $12 million from the Western Australian government’s Kimberley Science and Conservation Strategy co-invested by the WAMSI partners and supported by the Traditional Owners of the Kimberley.

Kimberley Marine Research Program