Spatial and trophic ecology of coastal sharks in the Anthropocene
Creators: name: Viera Niella, Yuri
Publisher: name: Macquarie University
Year: 2024
Subjects: classificationCode: 399999
subject: Other education not elsewhere classified

description: The planet has been altered severely by humanity that the current era has been declared the Anthropocene, a new epoch characterised by the overwhelming influence of humans upon nature. These impacts are driving broad ecosystemic effects including deleterious consequences for humans themselves through negative feedback loops. Of the suite of human impacts, climate change is possibly the broadest in scope and in the marine environment is demonstrably causing range shifts for many species. These changes are exacerbated by habitat alteration due to coastal urbanisation. In the marine environment, western boundary currents are warming quickly in response to climate change, of which the East Australian Current is changing the most rapidly. Large-bodied sharks are mobile predators and often closely associated with particular thermal gradients. Accordingly, large sharks are very likely to change their habitat range in response to ocean warming. Since coastal species are frequently involved in incidents with people there is particularly high interest in understanding their ecology and how this may be changing during the Anthropocene. In section one, an investigation of trophic ecology in juvenile bull sharks (<i>Carcharhinus leucas</i>) using stable isotope analyses reveals that fast turnover tissues and multiple-tracer techniques are needed to overcome the influence of maternal provisioning upon juvenile isotopic signatures. I also show that juvenile bull sharks rely on estuarine habitats which are threatened by climate change and urbanization, thereby identifying potential future ecological impacts upon the species. Section two describes the development of a new R package (Refined Shortest Paths – RSP) to analyse fine-scale acoustic telemetry data in complex aquatic environments constrained by land masses (i.e. estuaries and archipelagos). RSP takes these important barriers into account and so recreates more biologically plausible movements of tracked animals. RSP was then applied to predator-prey interactions between bull sharks and several potential prey teleosts in the most urbanized estuary in Australia (Sydney Harbour). In the following section, data from commercial fisheries, satellite and acoustic telemetry were used to investigate the environmental drivers of long-term redistribution of bull and tiger (<i>Galeocerdo cuvier</i>) sharks along the east coast of Australia and forecast responses to climate change which may influence their rates of interaction with water users. The final section is focussed on shark bite mitigation and shark ecology. An evidence-based approach is used to propose alternative strategies to government programs for mitigating risk of shark bites on Réunion Island, western Indian Ocean, and in the New South Wales Shark Meshing Program, Australia. Overall, in this thesis I identified that climate change and urbanization are impacting shark ecology, either directly through the alteration of key nursery habitats they rely upon for food, or indirectly with underwater noise affecting spatial overlap with potential prey. Climate change is leading to shark redistributions towards higher latitudes along the south-eastern coast of Australia, through alterations in water temperatures and current dynamics. The magnitude and speed of such changes may vary intra-specifically among biological classes (i.e. different sexes and age groups), and this should be accounted for to develop effective management strategies. As shark species move southwards along the south-eastern coast of Australia and remain there for longer periods increased inter and intra-specific competition are likely to occur, and this research helps to encapsulate what future scenarios might look like. Technology is a great asset in forecasting trends in animal movements (i.e. through telemetry transmitters and remote sensing) under the influence of Anthropogenic disturbance, and can help enhance coexistence between sharks and people by replacing traditional lethal shark bite mitigation strategies with non-lethal approaches (e.g. drones taking the place of shark nets).