Ecology and social structure of southern Australian bottlenose dolphins (Tursiops sp.) along Adelaide’s metropolitan coast

Author: Nikki Zanardo

Zanardo, Nikki, 2018 Ecology and social structure of southern Australian bottlenose dolphins (Tursiops sp.) along Adelaide’s metropolitan coast, Flinders University, College of Science and Engineering

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Little is known about the ecology and behaviour of southern Australian bottlenose dolphins (Tursiops sp.), which hinders informed decision-making concerning their conservation and management. This is particularly important considering their coastal distribution, which puts them under threat from a range of anthropogenic activities (Chapter 1). Here, I used boat surveys, photo identification methods and biopsy sampling to investigate the (1) site fidelity, residency and abundance (Chapter 2), (2) habitat use and distribution (Chapter 3), and (3) socio-genetic structure (Chapter 4) of southern Australian bottlenose dolphins in coastal waters of Adelaide, South Australia. Systematic boat-based surveys were conducted between December 2012 and August 2014, following predetermined zig-zag line transects. Surveys covered a total of 40 km of coastline and extended up to 7 km offshore, covering approximately 195 km2 of Adelaide’s metropolitan coastal waters. A total of 83 survey days were completed, with 244 distinctly marked individuals identified: 69 individuals (28%) were sighted only once and 175 (72%) were sighted on more than one occasion. In addition, 70 biopsy samples were obtained from individual animals. In Chapter two, I used the photo-identification data collected to estimate site fidelity, residency and abundance using agglomerative hierarchical clustering, lagged identification rates and capture-recapture models. Sighting rates and agglomerative hierarchical cluster analysis categorized individuals into specific groups of site fidelity, with 119 occasional visitors, 96 seasonal residents and 29 year-round residents. Lagged identification rates indicated that these dolphins used the study area regularly from year to year following a model of emigration and re-immigration. Abundance estimates obtained from multi-sample closed capture-recapture models ranged from 95 individuals (S.E. ± 45.20) in winter 2013 to 239 (S.E. ± 54.91) in summer 2014. In Chapter three, I identified areas of high probability of occurrence in relation eco-geographical variables using an ensemble modelling approach that combined results from three modelling techniques (generalised linear models, generalised additive models, and maximum entropy). Seasonal variation in habitat use along the metropolitan coast appears to be influenced by water depth and benthic habitat. Further, core feeding areas of dolphins overlapped considerably with areas of high probability of occurrence. Thus, I suggest that prey availability is an important driver influencing the seasonal variation in dolphin distribution along Adelaide’s metropolitan coast. In Chapter four, I use generalized affiliation indices and social network analysis to investigate social cohesion, intrapopulation community structure and potential drivers of associations between individuals. I demonstrate that individuals are subdivided into two socially and spatially segregated communities, comprising a northern shallow-water community and a southern deep-water community. Community membership also appears to be influenced by genetic relatedness, but patterns differed between females and males. While females had a significantly greater genetic relatedness within communities than between communities, this was not the case for the males and suggests that other factors may be of more importance for them. Altogether these findings suggest that southern Australian bottlenose dolphins along Adelaide’s metropolitan coast exhibit fission-fusion social traits similar to other coastal bottlenose dolphin populations. I then discuss how this information can be used to inform the conservation and management of bottlenose dolphins along the coastal waters of Adelaide (Chapter 5). The varying levels of site fidelity, residency, and identification of dolphin ‘hotspots’, highlights the importance of Adelaide’s metropolitan coast as a habitat for these dolphins. Management strategies should be implemented, to restrict frequent interactions with recreational fishing, boating and other water activities. As these bottlenose dolphins also appear to spend considerable time outside the study area, future research, conservation and management efforts of this population must take into account anthropogenic activities within Adelaide’s metropolitan coast and its adjacencies in Gulf St Vincent.

Keywords: Gulf St Vincent, Conservation planning, Coastal dolphins, Marine mammals

Subject: Biological Sciences thesis

Thesis type: Doctor of Philosophy
Completed: 2018
School: College of Science and Engineering
Supervisor: Luciana Moller