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

dc.contributor.authorTowner, Alison V.
dc.contributor.authorUnderhill, Les G.
dc.contributor.authorJewell, Oliver Joseph David
dc.contributor.authorSmale, Malcolm J.
dc.date.accessioned2013-10-08T06:42:08Z
dc.date.available2013-10-08T06:42:08Z
dc.date.issued2013-08-12
dc.description.abstractThe 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 Nin˜ o/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 humanwhite shark interactions.en_US
dc.description.librarianam2013en_US
dc.description.sponsorshipAVT acknowledges support from the Dyer Island Conservation Trust. LGU acknowledges support from the University of Cape Town Research Committee and the Oppenheimer Memorial Trust. OJDJ was supported by the Dyer Island Conservation Trust. MJS was supported by Bayworld museum.en_US
dc.description.urihttp://www.plosone.orgen_US
dc.identifier.citationTowner AV, Underhill LG, Jewell OJD, Smale MJ (2013) Environmental Influences on the Abundance and Sexual Composition of White Sharks Carcharodon carcharias in Gansbaai, South Africa. PLoS ONE 8(8): e71197. DOI: 10.1371/journal.pone.0071197en_US
dc.identifier.issn1932-6203
dc.identifier.other10.1371/journal.pone.0071197
dc.identifier.urihttp://hdl.handle.net/2263/31940
dc.language.isoenen_US
dc.publisherPublic Library of Scienceen_US
dc.rights© 2013 Towner et al. This is an open-access article distributed under the terms of the Creative Commons Attribution Licenseen_US
dc.subjectGansbaai, South Africaen_US
dc.subjectWhite shark (Carcharodon carcharias)en_US
dc.subjectEnvironmental influencesen_US
dc.titleEnvironmental influences on the abundance and sexual composition of white sharks Carcharodon carcharias in Gansbaai, South Africaen_US
dc.typeArticleen_US

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