Australian snubfin dolphins in the Kimberley appear to form at least three genetic populations that require careful management, according to new research.
The snubfin and humpback dolphin are unique to shallow, coastal waters of northern Australia and southern New Guinea. Both species are found off the coast of the Kimberley, though little is known of their numbers, key habitats and movements.
Over the past three years, a Western Australian Marine Science Institution, Kimberley Marine Research Program project has been working to answer some of these questions, by surveying local populations, collecting genetic samples, and developing new tools to help monitor these elusive species.
The research team from Murdoch and Curtin universities found that both snubfin and humpback dolphins occurred at all sites surveyed, although in varying numbers.
|The team conducted different fieldwork in a number of locations across the Kimberley, and presented data on dolphin relative abundance (R), population genetic structure (G) and/or passive acoustic monitoring (A).
Humpback dolphins were observed in similarly low numbers at most sites, while snubfin dolphins appeared to occur in greater numbers at a few discrete locations.
Small local populations of snubfins were apparent at Cone Bay and the Prince Regent River; however, previous research showed the Dampier Peninsula sites of Roebuck and Cygnet Bay to support greater numbers, highlighting these sites as key habitats for snubfin dolphins.
Genetic analyses, led by Murdoch University’s Dr. Alex Brown, showed that not all snubfin dolphins in the Kimberley could be considered the same population.
|Using the biopsy darting system to collect dolphin genetic samples in Cone Bay, with assistance from Dambimangari Ranger Edmund Jungine. Photo: Alex Brown.
Evidence suggests that there is very limited movement of snubfin dolphins between Roebuck Bay and King Sound, and that animals sampled further north and east may represent a third genetic population.
Analyses of humpback dolphin genetic samples revealed a lack of gene flow between animals sampled in the Kimberley and the Pilbara regions.
“It’s important for decision makers to recognise this genetic structure in order to minimise any threats to small, isolated, local populations,” Dr. Brown said. “For both species, more genetic samples are required in the north/east of the Kimberley to better understand the connectivity of local populations.”
“However, monitoring these species can be tricky, particularly in areas where they are unfamiliar with and shy of boats,” Dr Brown said.
Several scientists in the dolphin project team have been working on this problem by exploring the use of passive acoustic monitoring to detect and monitor dolphin presence and use of particular areas.
|Acoustic data loggers, developed by Curtin University, were deployed for up to three weeks at Cygnet and Roebuck Bay, recording dolphin vocalisations and allowing the Curtin researchers to characterise the natural soundscape of the two areas. Photo: Alex Brown.
This new technology was able to pick up the whistles and clicks that dolphins make as they travel, forage and socialise, and the research team uncovered several new whistle types to add the species’ repertoire. However, more work is required before the two species can be efficiently distinguished and the number of animals present can be identified.
|An audiogram of echolocation clicks, pulsed ‘buzz’ sounds, and tonal whistles
recorded in the presence of snubfin dolphins.
A key part of this research was collaborating with local stakeholders. The research team collected data alongside Yawuru, Bardi-Jawi, Dambimangari and Balanggarra Traditional Owners, as well as regional Parks and Wildlife staff, generating valuable training opportunities.
|Murdoch University researchers work alongside Balanggarra Rangers Wesley Alberts and Wayne Moore to collect individual identification photos of humpback dolphins in the Cambridge Gulf. Photo: Alex Brown.
The data collected, along with the improved local collaboration, will help with future research and monitoring in the region.
The full research findings presentation is available on the WAMSI dolphin project webpage.
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.