Population demographics and spatial ecology of Indo-Pacific bottlenose dolphins (Tursiops aduncus) inhabiting coastal waters at the North West Cape, Western Australia

Author: Rebecca Haughey

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Haughey, Rebecca, 2021 Population demographics and spatial ecology of Indo-Pacific bottlenose dolphins (Tursiops aduncus) inhabiting coastal waters at the North West Cape, Western Australia, Flinders University, College of Science and Engineering

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Abstract

Increasing human presence in coastal areas is threatening these important nearshore ecosystems and their associated fauna. Due to their coastal distribution and slow life history, inshore dolphins are vulnerable to anthropogenic activities associated with coastal areas. This is particularly the case in north-western Australia, a rapidly changing region with limited information on the status of the Near Threatened Indo-Pacific (IP) bottlenose dolphin (Tursiops aduncus) inhabiting its coastal waters. The North West Cape (NWC) in Western Australia (WA) is a diverse environment with mixed levels of protection including waters within and outside the Ningaloo Marine Park (NMP). Preliminary evidence indicated that the NWC is of importance to IP bottlenose dolphins, but information about their ecology is lacking. In this study, I used boat-based surveys, photo-identification, behavioural observations and population and species distribution modelling techniques to investigate IP bottlenose dolphin abundance, site fidelity, distribution, and habitat use. This study provides the first demographic assessment of IP bottlenose dolphins at the NWC, identifies areas of high probability of dolphin occurrence, and reveals key areas for foraging, resting, and travelling. Overall, the results from my study improve the understanding of IP bottlenose dolphin ecology and provide the basic knowledge required to enhance their conservation and management in this region.

Capture-recapture modelling and site fidelity indexes revealed that a large IP bottlenose dolphin population (311 – 370 individuals) inhabits these coastal waters (Chapter 2). The population is composed of a large proportion of dolphins that use the area occasionally (non-residents, 58%), and a smaller proportion of dolphins that use the area regularly (residents, 42%) (Chapter 2). The large number of both resident and non-resident bottlenose dolphins found throughout the coastal waters off the NWC suggest this area, as well as neighbouring waters outside my study area, are of high importance to this species. Species distribution modelling of IP bottlenose dolphins revealed a strong preference for shallow waters (7 – 13 m deep), less than 2000 m from the coast and up to 7000 m from boat launch sites (Chapter 3). Areas of high probability of occurrence for dolphins varied seasonally but generally extended from the tip of the NWC, down the eastern side, overlapping with designated Sanctuary Zones as well as occurring in waters beyond the boundaries of the NMP (Chapter 3). The spatial distribution patterns of IP bottlenose dolphins at the NWC are likely the result of prey availability and predation risk, with dolphins likely choosing the safest and most productive waters. Distribution modelling incorporating behavioural data, in fact, revealed that coastal waters of the NWC are functionally important for resting, foraging and travelling behaviours (Chapter 4). Core areas for each behaviour were located both within the NMP and outside the current marine park boundaries. Resting schools of IP bottlenose dolphins showed a preference for shallow waters in designated Sanctuary Zones (Chapter 4). I hypothesise that IP bottlenose dolphins are selecting the most appropriate habitat to reduce the threat of predation in times of reduced vigilance and increased vulnerability. Foraging and travelling schools were more widespread throughout the study area. Foraging was more likely to occur 3000 – 5000 m from boat ramps in areas of moderate seabed slope (Chapter 4). The characteristics of the seascape (i.e. seabed slope and oceanographic conditions) at these locations likely leads to the aggregation of important prey species for IP bottlenose dolphins and are most conducive to the capture of prey. Travelling schools were more likely to occur 1000 – 2000 m from the coast and in water depths of 7 – 12 m, but as deep as 20 m (Chapter 4). These travelling areas represent important corridors between foraging and resting patches.

Findings from my study indicate that the study area, as well as adjacent waters in the wider NWC region, are of high importance to IP bottlenose dolphins, highlighting the potential vulnerability of this species to increasing and cumulative anthropogenic stressors associated with these areas. This study provides crucial baseline information that can be incorporated by wildlife agencies into future management plans for the NWC region. Such information is crucial for informing effective conservation strategies to mitigate impacts from repeated and cumulative anthropogenic impacts in the region. Additionally, I have provided recommendations for future research directions that should advance our knowledge of IP bottlenose dolphin ecology and enhance their conservation in the wild.

Keywords: abundance, site fidelity, Ningaloo Reef, Exmouth Gulf, Indo-Pacific bottlenose dolphins, Tursiops aduncus, species distribution modelling, Marine Protected Area, conservation, management, spatial ecology

Subject: Environmental Science thesis

Thesis type: Doctor of Philosophy
Completed: 2021
School: College of Science and Engineering
Supervisor: Guido Parra