Environmental factors affecting sexual and size segregation, and the effect of baiting on the natural behaviours, of great white sharks, Carcharodon Carcharias, at the Neptune Islands, South Australia

Publication Type:
Thesis
Issue Date:
2006
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NO FULL TEXT AVAILABLE. Access is restricted indefinitely. ----- The behaviour of large predators in marine environments has been little studied, but is likely to have great influence on their own population dynamics and that of their prey. In this study, the ecology and behaviour of the white shark, Carcharodon carcharias, particularly in relation to patterns of sexual and size segregation and bait conditioning, were investigated at the Neptune Islands, South Australia. It was also aimed to discern which seasonal and environmental factors were acting to influence the presence or absence of individuals at certain times of the year. White sharks segregate by sex and size on a seasonal basis at the Neptune Islands. 126 different sharks were sighted at the Neptune Islands between April 2001 and February 2004. The population structure at the Neptune Islands was distinctly segregated, both in terms of sex and size of sharks present, and both forms of segregation were primarily affected by sea surface temperature. Mature females constituted only 2.4% of the total sharks observed. The abundances of females of both maturity classes were skewed towards the higher sea surface temperatures experienced. Sea surface temperature was found to have a negative linear relationship with sub-adult and mature male numbers. Hypotheses for the observed segregations, such as differing thermal tolerances, differentiation between the sexes in relation to skin thickness, differing dietary requirements, reproductive fitness and intraspecific competition, are discussed. The significance of these findings to current and future management plans for this species is considered in regards to population monitoring and reduction of incidental mortality. The results of the conditioning study should aid to rebuff ambiguities in available data conducted under baited conditions. There was little correlative evidence to suggest that conditioning ws occurring to any large degree and it was inferred that sharks under baited conditions are not significantly influenced by the presence of bait and chum to make the data unreliable. Therefore, it is contended that data collected under baited conditions are representative of natural shark behaviours. Although habituation occurred in less than 5% of individuals, suggestions to ensure minimal disturbance of the population in respect to chumming are offered.
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