PhD completion by Dr. Delphine Chabanne: Indo-Pacific bottlenose dolphins in Perth metropolitan waters

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Congratulations to Dr. Delphine Chabanne for the completion of her PhD: “Distribution, abundance, social and genetic structures of Indo-Pacific bottlenose dolphins (Tursiops aduncus) in Perth metropolitan waters, Western Australia”.

Supervisors: Prof. Lars Bejder, Dr Hugh Finn, Prof. William B. Sherwin.

Delphine graduated last week, following formal conferral of her degree.

Her PhD focused on providing the scientific basis for decision-making around ‘units to conserve’ for bottlenose dolphins in the Perth region. There were multiple imperatives for this research, including the concerns raised by the unusual mortality event in 2009, rapid human population growth in the region, and proposed coastal developments.

This research involved four years of fieldwork, and much credit goes to the many hard-working field assistants who made such data collection possible.

Abstract

In heterogeneous coastal and estuarine environments, dolphins are exposed to varying levels of human activities. Consequently, it is important to identify and characterise fine-scale population structuring based on ecological, social, spatial and genetic data to develop appropriate conservation and management strategies. This thesis focused on identifying subpopulations of Indo-Pacific bottlenose dolphins (Tursiops aduncus) inhabiting Perth waters, Western Australia (WA). Using spatial and social data collected over four years of boat-based photo-identification surveys, I: i) estimated abundances, survival and movement rates using a Multistate Closed Robust Design approach; and ii) examined the social structure and home range using social association and network analyses. I used microsatellite loci and mtDNA markers to investigate the genetic population structure of dolphins at metropolitan (Perth) and regional (c. 1000 km of coastline) scales. High capture probabilities, high survival and constant abundances described a subpopulation with high fidelity in an estuary. In contrast, low captures, emigration and fluctuating abundances suggested transient use and low fidelity in an open coastline region. Overall, dolphins formed four socially and geographically distinct, mixed-sex subpopulations that varied in association strength, site fidelity and residency patterns. Curiously, home range overlap and genetic relatedness did not affect the association patterns. In Perth metropolitan waters, a source-sink relationship was suggested between a subpopulation inhabiting a semi-enclosed embayment and three other subpopulations, including the estuarine subpopulation. On a broader scale, the Perth metapopulation was genetically distinct from other populations along the WA southwestern coastline, with little to no migration from and into other populations. The subpopulations present in Perth waters should each be regarded as a distinct management unit, with a particular focus on protecting the estuarine subpopulation, which is small, has limited connection with adjacent subpopulations and is more vulnerable because of the intensity and diversity of anthropogenic threats present in the estuary.

The full thesis can be accessed through Murdoch University’s research repository here.

Fieldwork tasks: Photo-identification (left); Biopsy sampling (centre); Retrieving a skin/blubber sample freshly collected (right).

Publications arising from this work:

A further publication from this thesis is currently in prep, which will present the genetic differentiation between socially and spatially subpopulations of dolphins in Perth region.

This research was primarily funded by the Swan River Trust and multiple donations made by the Fremantle Ports. Delphine was supported by an Australian Postgraduate Award (APA) with Murdoch University Strategic Top-up. We are grateful to the Sailing Club in Fremantle for access to the boat ramp. Special thanks go to Prof. Ken Pollock for his assistance and guidance since the start of this project in 2011.

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