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

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dc.contributor.authorTowner, Alison Ven_ZA
dc.contributor.authorUnderhill, Les Gen_ZA
dc.contributor.authorJewell, Oliver J Den_ZA
dc.contributor.authorSmale, Malcolm Jen_ZA
dc.date.accessioned2015-11-10T14:47:32Z
dc.date.available2015-11-10T14:47:32Z
dc.date.issued2013en_ZA
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 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.en_ZA
dc.identifier.apacitationTowner, A. V., Underhill, L. G., Jewell, O. J. D., & Smale, M. J. (2013). Environmental influences on the abundance and sexual composition of white sharks Carcharodon carcharias in Gansbaai, South Africa. <i>PLoS One</i>, http://hdl.handle.net/11427/14829en_ZA
dc.identifier.chicagocitationTowner, Alison V, Les G Underhill, Oliver J D Jewell, and Malcolm J Smale "Environmental influences on the abundance and sexual composition of white sharks Carcharodon carcharias in Gansbaai, South Africa." <i>PLoS One</i> (2013) http://hdl.handle.net/11427/14829en_ZA
dc.identifier.citationTowner, A. V., Underhill, L. G., Jewell, O. J., & Smale, M. J. (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_ZA
dc.identifier.ris TY - Journal Article AU - Towner, Alison V AU - Underhill, Les G AU - Jewell, Oliver J D AU - Smale, Malcolm J AB - 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. DA - 2013 DB - OpenUCT DO - 10.1371/journal.pone.0071197 DP - University of Cape Town J1 - PLoS One LK - https://open.uct.ac.za PB - University of Cape Town PY - 2013 T1 - Environmental influences on the abundance and sexual composition of white sharks Carcharodon carcharias in Gansbaai, South Africa TI - Environmental influences on the abundance and sexual composition of white sharks Carcharodon carcharias in Gansbaai, South Africa UR - http://hdl.handle.net/11427/14829 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/14829
dc.identifier.urihttp://dx.doi.org/10.1371/journal.pone.0071197
dc.identifier.vancouvercitationTowner AV, Underhill LG, Jewell OJD, Smale MJ. Environmental influences on the abundance and sexual composition of white sharks Carcharodon carcharias in Gansbaai, South Africa. PLoS One. 2013; http://hdl.handle.net/11427/14829.en_ZA
dc.language.isoengen_ZA
dc.publisherPublic Library of Scienceen_ZA
dc.publisher.departmentAnimal Demography Unit (ADU)en_ZA
dc.publisher.facultyFaculty of Scienceen_ZA
dc.publisher.institutionUniversity of Cape Town
dc.rightsThis is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.en_ZA
dc.rights.holder© 2013 Towner et alen_ZA
dc.rights.urihttp://creativecommons.org/licenses/by/4.0en_ZA
dc.sourcePLoS Oneen_ZA
dc.source.urihttp://journals.plos.org/plosoneen_ZA
dc.subject.otherSharksen_ZA
dc.subject.otherEl Niño-Southern Oscillationen_ZA
dc.subject.otherSurface temperatureen_ZA
dc.subject.otherPredationen_ZA
dc.subject.otherGeneralized linear modelen_ZA
dc.subject.otherMarine fishen_ZA
dc.subject.otherSea wateren_ZA
dc.subject.otherSeasonsen_ZA
dc.titleEnvironmental influences on the abundance and sexual composition of white sharks Carcharodon carcharias in Gansbaai, South Africaen_ZA
dc.typeJournal Articleen_ZA
uct.type.filetypeText
uct.type.filetypeImage
uct.type.publicationResearchen_ZA
uct.type.resourceArticleen_ZA
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