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Publication Details
AFRICAN RESEARCH NEXUS
SHINING A SPOTLIGHT ON AFRICAN RESEARCH
Environmental Influences on the Abundance and Sexual Composition of White Sharks Carcharodon carcharias in Gansbaai, South Africa
PLoS ONE, Volume 8, No. 8, Article e71197, Year 2013
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Description
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. © 2013 Towner et al.
Authors & Co-Authors
Towner, Alison V.
South Africa, Kleinbaai, Gansbaai
Dyer Island Conservation Trust
South Africa, Cape Town
University of Cape Town
Underhill, Leslie Gordon
South Africa, Cape Town
University of Cape Town
Jewell, Oliver J.D.
South Africa, Kleinbaai, Gansbaai
Dyer Island Conservation Trust
South Africa, Pretoria
University of Pretoria
Smale, Malcolme John
South Africa, Humewood
Port Elizabeth Museum
South Africa, Gqeberha
Nelson Mandela University
Statistics
Citations: 36
Authors: 4
Affiliations: 5
Identifiers
Doi:
10.1371/journal.pone.0071197
e-ISSN:
19326203
Research Areas
Environmental
Sexual And Reproductive Health
Study Locations
South Africa
Participants Gender
Male
Female