Behavioural ecology of white sharks carcharodon carcharias in False Bay, South Africa: towards improved management and conservation of a threatened apex predator
Doctoral Thesis
2014
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University of Cape Town
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Abstract
The coastal waters off South Africa support a significant proportion of the global white shark population, with at least four well-established coastal aggregation sites. How critical these sites are to the southern African and hence global white shark population depends to a large extent, on their levels of residency a nd site fidelity, in relation to potential threats. Here, I attempt to provide such data by studying the annual and seasonal presence of white sharks in False Bay. From 1 April 2004 - 31 December 2007, a total of 68 (46 female, 22 male) sharks, ranging in length from 1.7 to 5 m, were tagged with acoustic transmitters and monitored on an array of 30 receivers, distributed along the Inshore region of False Bay and at Seal Island, for a maximum of 1349 days. I used generalized linear mixed effects models to investigate the effects of season, habitat type, sex, size and time of day on shark presence. Most tagged sharks were immature animals, some of which were detected in the Bay in all months and across all years. In autumn and winter, males and females aggregated around Seal Island, where they fed predominantly on young-of-the-year seals. Sharks, regardless of sex or size, over-dispersed on the South side of the Island at sunrise, where the probability of encountering predator-naïve seals was highest. Shark presence at Seal Island mirrored the spatial distribution of predation around the Island, which was highest on the South side within 400 m of the Island, and at sunrise. In spring and summer, there was marked sexual segregation in presence, with females frequenting the Inshore areas and males seldom being detected in the Bay . Within the Inshore region, female white sharks showed a preference for beach, compared to rocky, mixed and harbour habitats. The preference for beach habitat likely reflects a combination of high prey availability, in addition to an open habitat suitable for detecting and securing prey. Overall, the results confirm False Bay as a critical area for white shark conservation as both sexes, across a range of sizes, show high levels of fidelity to the Bay.
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Reference:
Kock, A. 2014. Behavioural ecology of white sharks carcharodon carcharias in False Bay, South Africa: towards improved management and conservation of a threatened apex predator. University of Cape Town.