Abstract
Prey availability is a driving force in the distribution, behavior, and movement patterns of predators. Relative abundance, concentration, and energy content of prey all influence predator choice in space use. Bottlenose dolphin (Tursiops aduncus) abundance in the nearshore waters of Bunbury, Western Australia is found to be higher during the summer months (Smith et al, in prep). It was therefore hypothesized that the seasonal movement patterns of dolphins is influenced by higher quantity or quality of available prey during the same temporal period. To ascertain the potential influence of prey availability (quantity and diversity) and quality (calorific content) on the seasonal movement patterns of dolphins, the relative abundance and diversity of fish were sampled in three near shore habitats (coastal ocean, bay and estuary) using three fishing techniques: z-traps, beach seines, and gillnets, which targeted different prey species. Sampling was conducted in three summer and two winter seasons between 2008-2010. Three replicate samples were taken at each of the three sampling sites per season. Seasonal, annual, and regional comparisons in fish assemblage, abundance and calorific content were made. Seasonal trends in fish abundance (numbers and biomass of fish caught) and available calories vary depending on the species in question. Overall, there appears to be higher biomass and higher density values of calories available to the dolphins in the winter months. It appears that dolphin abundance is influenced more by social or physiological factors such as predator avoidance or breeding opportunities in summer (when the majority of breeding occurs (Smith et al. in prep)) and prey availability in winter. Understanding relationships between the dolphins and local fish populations is critical in managing the substantial fisheries of the region, as well as managing other factors, such as coastal development, that could affect dolphin and fish behavior.