AbstractsBiology & Animal Science

Despite their prominence as species of great interest and conservation significance, currently our understanding of shark movement patterns and their ecological role as predators on small Odontocete populations is far from complete. The first component of my research investigated the movement patterns of the four main commercial species (sandbar, Carcharhinus plumbeus; dusky, Carcharhinus obscurus; whiskery, Furgaleus macki; gummy, Mustelus antarcticus) and several species occasionally caught off the coast of Western Australia (Chapter 2). I analysed long-term (1994 to 2013), conventional tagging data collected by the Department of Fisheries, Western Australia to provide a detailed account of observed movement patterns. The second component of my research investigated the predatory role of sharks on bottlenose dolphins (Tursiops aduncus) off Bunbury, Western Australia (Chapter 3). I examined the prevalence of shark bites on systematically photographed dolphins over an eight year period (2007 to 2014). I also attempted to identify the shark species responsible for the attacks by seeking the expert opinions of three independent reviewers on the bite marks. The analyses of movement patterns from the long-term tagging data (Chapter 2) found mean displacements of < 250 km for the four main commercial species. However, occasional displacements of more than 2,000 km were also observed for all four species. Displacement was positively correlated with time at liberty, size (fork length) and release condition. The swimming speed varied significantly between species, with faster movements observed for larger Carcharhinid sharks. Furthermore, significant differences in sex ratios at release and recapture were observed for gummy and whiskery sharks. A significantly higher proportion of females were released and recaptured for both species. Although, fork length was found to significantly vary for non-recaptured and recaptured sandbar and dusky sharks, results from the analyses were disregarded due to bias gear-selectivity and inaccurate measurements reported by fishermen. The highest recapture frequency for all other species occasionally caught was less than ten. Maximum displacements ranged from 0.70 to 1,143 km, these displacements were observed by wobbegongs (Orectolobus sp.) and copper whaler (Carcharhinus brachyurus) sharks, respectively. Maximum time at liberty ranged from 4 to 5,245 days for nervous (Carcharhinus cautus) and tiger (Galeocerdo cuvier) sharks, respectively. The estimated maximum swimming speed for occasionally caught species peaked at 0.42 km/hr for copper whaler (Carcharhinus brachyurus) sharks. Swimming speeds for all other species were less than 0.03 km/hr. No statistical analyses were completed for these species. Analyses of the prevalence of external injuries believed to have been inflicted by sharks (Chapter 3) found that the total bite mark frequencies of systematically photographed dolphins varied significantly among age classes (calves, juveniles, adults) with the highest frequency of…