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Conservation biology of bottlenose dolphins (Tursiops sp.) in Perth metropolitan waters

Finn, Hugh (2005) Conservation biology of bottlenose dolphins (Tursiops sp.) in Perth metropolitan waters. PhD thesis, Murdoch University.

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      Abstract

      This thesis examines two potential conservation problems for a residential sub-population of ~75 bottlenose dolphins (Tursiops sp.) in Cockburn Sound, a small embayment within the southern metropolitan waters of Perth, Western Australia: (1) human-induced habitat change and (2) illegal feeding (i.e. unregulated provisioning) of dolphins. The work is important because Cockburn Sound is the most intensively utilised marine environment in Western Australia and industrial, commercial, and recreational uses of the area will intensify in coming decades. These considerations, coupled with the demographic and ecological vulnerability of residential populations of small cetaceans, suggested a risk of population decline without a more informed scientific basis for management. This study (2000 - 2003) complemented an earlier study of the Cockburn Sound dolphins (1993 - 1997) to provide a decade-long longitudinal study of the population. The original contributions of this study relate to: (a) the foraging ecology of dolphins;(b) the effects and mechanisms of human-dolphin interaction, particularly interactions based on unregulated provisioning; and (c) an integration of previous research and other information.

      Studies of the foraging ecology of dolphins within Cockburn Sound were undertaken between 2000-2 to determine the areas used by dolphins and their feeding behaviours so that the implications of human-induced habitat change could be assessed. These studies used belt transect sampling and event-specific sampling of foraging aggregations of dolphins to quantify the foraging habitat use of dolphins within the Sound and to characterise spatial and temporal patterns in aggregations of foraging dolphins. The results showed that the density of foraging dolphins varied significantly across habitats and that foraging aggregations consistently occur in an area known as the Kwinana Shelf during the austral autumn-spring period. The studies also suggested that the foraging ecology of dolphins in Cockburn Sound reflects the consistent utilisation of both: (a) low-density prey species (i.e. individual or weakly-schooling prey) and (b) high-density prey species (i.e. schooling species such as forage fish). These findings indicate that ecosystem-based conservations of the population should consider the conservation requirements of dolphin prey species and the ecological integrity of key foraging habitats like the Kwinana Shelf.

      Human-dolphin interactions based on the illegal feeding of dolphins in Cockburn Sound escalated between 1993 and 2003. By 2003, a total of 14 individuals exhibited behaviours indicative of conditioning to human interaction by food reinforcement, including some individuals that engaged in provisioning interactions on a chronic (i.e. long-term) basis. Observations of the effects of unregulated provisioning indicated that: (a) provisioned dolphins sustained increased higher rates of human-induced injury than non-provisioned dolphins and (b) provisioning was associated with substantial and enduring behavioural changes including changes in ranging and association patterns. Other observations of human-induced injury in Cockburn Sound included seven instances of calf entanglement. These findings indicate that the effects of illegal feeding and other forms of direct human-dolphin interaction (e.g. entanglement) could achieve biological significance for the population.

      The possible contribution of (a) human influences, (b) social learning, and (c) behavioural propensities (e.g. age and sex) on the acquisition of an attraction response to human provisioning was examined through logistic regression analysis using age, sex, use of high-boat density areas, and the number of close associates that were previously provisioned as predictor variables and the acquisition of an attraction response as the dependent variable. This analysis was supplemented by behavioural observations of interactions between provisioned and naive individuals during provisioning interactions. The results supported three findings: (1) a relatively high level of exposure to human provisioners was a significant predictor for the acquisition of an attraction response by dolphins; (2) social learning contributed to the acquisition of an attraction response in those individuals that more frequently utilised high-boat density areas; and (3) the potential contribution of behavioural propensities relating to age and sex was uncertain. These conclusions suggest that the acquisition of an attraction response to human provisioning can best be understood as the outcome of a complex of interacting factors.

      The findings also indicate: (a) the management value of individual-specific and longitudinal data for the management of harmful human-wildlife interactions and (b) the potential for social learning to contribute to the development and persistence of these interactions. The findings of this study indicate that population decline in Cockburn Sound could be induced by: (1) a reduction in the Sound?s environmental carrying capacity or (2) mortality, injury, and behavioural changes resulting from interactions with humans. The potential for such a decline and evidence demonstrating the harmful effects of human activities on dolphins supports the application of preventative approach to the management of illegal feeding and entanglement and a precautionary approach to environmental impact assessments of proposed developments. Mitigation of direct human-dolphins like illegal feeding requires an enforcement and education program to encourage more responsible human attitudes towards interactions with dolphins. Research on the ecology and composition of finfish assemblages and the trophic structure of the Kwinana shelf would assist efforts to mitigate the impact of human-induced habitat change.

      Publication Type: Thesis (PhD)
      Murdoch Affiliation: School of Biological Sciences and Biotechnology
      Supervisor: Calver, Michael
      URI: http://researchrepository.murdoch.edu.au/id/eprint/49
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