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M. L. Dicken, M. J. Smale, & A. J. Booth
We present the first quantitative study on the occurrence, size and sex of white sharks (Carcharodon carcharias) at Bird Island, in Algoa Bay. Twenty two boat trips were made to Bird Island between November 2009 and October 2011 to chum for sharks. A total of 53 sharks were observed over the study period ranging in size from 1.5 to 4. 5 m, with the majority (67.9%) being juveniles. The sex ratio of positively identified sharks was not significantly different from unity. In both study years sharks were only present in the winter months between April and November with a maximum of 1.2 sharks sighted per hour. A zero-altered model, comprising a logistic regression to model presence-absence and a log-normal generalized linear model for abundance showed that season explained the presence of sharks, peaking in mid-July, with abundance being significantly higher with higher barometric pressure. This study identified Bird Island as an important white shark aggregation site along the east coast of South Africa. These data are crucial not only to improve our understanding of white shark seasonal distribution and biology, but also for their long-term management and conservation in South Africa.
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