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

 

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dc.contributor.author Towner, Alison V en_ZA
dc.contributor.author Underhill, Les G en_ZA
dc.contributor.author Jewell, Oliver J D en_ZA
dc.contributor.author Smale, Malcolm J en_ZA
dc.date.accessioned 2015-11-10T14:47:32Z
dc.date.available 2015-11-10T14:47:32Z
dc.date.issued 2013 en_ZA
dc.identifier.citation Towner, 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.0071197 en_ZA
dc.identifier.uri http://hdl.handle.net/11427/14829
dc.identifier.uri http://dx.doi.org/10.1371/journal.pone.0071197
dc.description.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. en_ZA
dc.language.iso eng en_ZA
dc.publisher Public Library of Science en_ZA
dc.rights This 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.uri http://creativecommons.org/licenses/by/4.0 en_ZA
dc.source PLoS One en_ZA
dc.source.uri http://journals.plos.org/plosone en_ZA
dc.subject.other Sharks en_ZA
dc.subject.other El Niño-Southern Oscillation en_ZA
dc.subject.other Surface temperature en_ZA
dc.subject.other Predation en_ZA
dc.subject.other Generalized linear model en_ZA
dc.subject.other Marine fish en_ZA
dc.subject.other Sea water en_ZA
dc.subject.other Seasons en_ZA
dc.title Environmental influences on the abundance and sexual composition of white sharks Carcharodon carcharias in Gansbaai, South Africa en_ZA
dc.type Journal Article en_ZA
dc.rights.holder © 2013 Towner et al en_ZA
uct.type.publication Research en_ZA
uct.type.resource Article en_ZA
dc.publisher.institution University of Cape Town
dc.publisher.faculty Faculty of Science en_ZA
dc.publisher.department Animal Demography Unit (ADU) en_ZA
uct.type.filetype Text
uct.type.filetype Image
dc.identifier.apacitation Towner, 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/11427/14829 en_ZA
dc.identifier.chicagocitation Towner, 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/11427/14829 en_ZA
dc.identifier.vancouvercitation Towner 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.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


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This 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. Except where otherwise noted, this item's license is described as This 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.