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

机译：环境影响南非甘斯拜白鲨Carcharodon carcharias的丰度和性成分

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The seasonal occurrence of white sharks visiting Gansbaai, South Africa was investigated from 2007 to 2011 using sightingsfrom white shark cage diving boats. Generalized linear models were used to investigate the number of great white sharkssighted 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 andthermocline displacement, culminating in colder water temperatures, and shark sightings of both sexes were higher duringthe autumn and winter months (March–August). MEI, an index to quantify the strength of Southern Oscillation, differed inits effect on the recorded numbers of male and female white sharks, with highly significant interannual trends. This datasuggests that water temperature and climatic phenomena influence the abundance of white sharks at this coastal site. Inthis study, more females were seen in Gansbaai overall in warmer water/positive MEI years. Conversely, the opposite trendwas observed for males. In cool water years (2010 to 2011) sightings of male sharks were significantly higher than inprevious 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 environmentalparameters into predictive models may help identify times and localities of higher risk to bathers and help mitigate humanwhiteshark interactions.
机译：2007年至2011年，使用白鲨笼潜水船的目击调查了白鲨到南非Gansbaai的季节性发生。使用广义线性模型来研究每次旅行中大白鲨的数量与性别，月份，海面温度和多元El Nino /南方涛动（ENSO）指数（MEI）相关。由于风驱动的冷水上升和温床移动，夏季的水况比冬季多变，最终导致水温降低，在秋季和冬季（3月至8月），两性鲨鱼的目击率更高。 MEI是量化南方涛动强度的指标，它对记录的雄性和雌性白鲨数量的影响有所不同，并且具有极高的年际趋势。该数据表明，水温和气候现象影响了该沿海地区白鲨的数量。在这项研究中，在温暖的水/ MEI阳性年份中，在Gansbaai总体上看到了更多的女性。相反，男性则观察到相反的趋势。在凉水年份（2010年至2011年），发现雄性鲨鱼的人数明显高于往年。讨论了环境因素在大小和性别方面对鲨鱼生理的影响。这项研究的结果可能有助于沐浴者安全计划，因为将环境参数纳入预测模型可能有助于确定对沐浴者较高风险的时间和地点。并帮助减轻人与白鲨的互动。

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