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. 2013 Aug 12;8(8):e71197.
doi: 10.1371/journal.pone.0071197. eCollection 2013.

Environmental influences on the abundance and sexual composition of white sharks Carcharodon carcharias in Gansbaai, South Africa

Alison V Towner  1 , Les G Underhill, Oliver J D Jewell, Malcolm J Smale
Affiliations

Environmental influences on the abundance and sexual composition of white sharks Carcharodon carcharias in Gansbaai, South Africa

Alison V Towner et al. PLoS One. .

Abstract

The seasonal occurrence of white sharks visiting Gansbaai, South Africa was investigated from 2007 to 2011 using sightings from white shark cage diving boats. Generalized linear models were used to investigate the number of great white sharks sighted per trip in relation to sex, month, sea surface temperature and Multivariate El Niño/Southern Oscillation (ENSO) Indices (MEI). Water conditions are more variable in summer than winter due to wind-driven cold water upwelling and thermocline displacement, culminating in colder water temperatures, and shark sightings of both sexes were higher during the autumn and winter months (March-August). MEI, an index to quantify the strength of Southern Oscillation, differed in its effect on the recorded numbers of male and female white sharks, with highly significant interannual trends. This data suggests that water temperature and climatic phenomena influence the abundance of white sharks at this coastal site. In this study, more females were seen in Gansbaai overall in warmer water/positive MEI years. Conversely, the opposite trend was observed for males. In cool water years (2010 to 2011) sightings of male sharks were significantly higher than in previous years. The influence of environmental factors on the physiology of sharks in terms of their size and sex is discussed. The findings of this study could contribute to bather safety programmes because the incorporation of environmental parameters into predictive models may help identify times and localities of higher risk to bathers and help mitigate human-white shark interactions.

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Conflict of interest statement

Competing Interests: This work was supported by Marine Dynamics Shark Tours (http://www.sharkwatchsa.com/en/home/) and the Dyer Island Conservation Trust (www.dict.org.za), these organisations are supported by donations from tourists and VW South Africa (www.vw.co.za). Marine Dynamics provided the platform to collect data from its shark cage diving trips and has also contributed to the study costs of AT and OJ’s Masters research. These authors continue to gain financial support from Marine Dynamics as they pursue future academic goals. This does not alter the authors' adherence to all the PLOS ONE policies on sharing data and materials.

Figures

Figure 1
Figure 1. Site Map showing the inshore and island region of Gansbaai.
This image was created by EDNA Interactive Ltd trading as EDNA: www.edna.uk.net.
Figure 2
Figure 2. Interannual variability in the mean number of male and female shark sightings per trip at Dyer Island, 2007 to 2011.
Figure 3
Figure 3. Interannual variability in the mean number of male and female shark sightings per trip at the inshore site in Gansbaai, 2007 to 2011.
Figure 4
Figure 4. Multivariate ENSO index (MEI) data 1950 to 2010 (Wolter and Timlin 2011 and NOAA).
Data sourced from www.noaa.com.
See this image and copyright information in PMC

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References

    1. Compagno LJV (2001) FAO species catalogue for fisheries purposes. No. 1. Sharks of the World: An annotated and illustrated catalogue of shark species known to date. Vol. 2. Bullhead, Mackerel and Carpet Sharks (Heterodontiformes, Lamniformes and Orectolobiformes). Food and Agricultural Organization of the United Nations (FAO) Rome, Italy, 269.
    1. Compagno LJV (1984) Sharks of the world. An annotated and illustrated catalogue of shark species known to date. Part 1 - Hexanchiformes to Lamniformes. FAO species catalogue. Vol. 4, FAO Fisheries Synopsis 125(4/1): 1–249.
    1. Carey FG, Kanwisher JW, Brazier O, Gabrielson G, Casey JG, et al. (1982) Temperature and activities of a white shark, Carcharodon carcharias . Copeia 1982: 254–260.
    1. Casey JG, Pratt HL (1985) Distribution of the white shark, Carcharodon carcharias, in the western North Atlantic. Mem Calif Acad Sci 9: 2–14.
    1. Compagno LJV (1987) Shark attack in South Africa. In: Stevens JD, editor. Sharks: An Illustrated Encyclopedic Survey by International Experts. Cape Town: Struik. 134–147.

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