Demographic differences in resource use are key components of population and species ecology across the animal kingdom. White sharks (Carcharodon carcharias) are migratory, apex predators, which have undergone significant population declines across their range. Understanding their ecology is key to ensuring that management strategies are effective. Here, we carry out the first stable isotope analyses of free-swimming white sharks in South Africa. Biopsies were collected in Gansbaai (34.5805°S, 19.3518°E) between February and July 2015. We used Stable Isotope Bayesian Ellipsis in R and traditional statistical analyses to quantify and compare isotopic niches of male and female sharks of two size classes, and analyse relationships between isotopic values and shark length. Our results reveal cryptic trophic differences between the sexes and life stages. Males, but not females, were inferred to feed in more offshore or westerly habitats as they grow larger, and only males exhibited evidence of an ontogenetic niche shift. Lack of relationship between δ13C, δ15N and female shark length may be caused by females exhibiting multiple migration and foraging strategies, and a greater propensity to travel further north. Sharks < 3 m had much wider, and more diverse niches than sharks > 3 m, drivers of which may include individual dietary specialisation and temporal factors. The differences in migratory and foraging behaviour between sexes, life stages, and individuals will affect their exposure to anthropogenic threats, and should be considered in management strategies.

中文翻译：

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性别、大小和同位素：顶级捕食者大白鲨 Carcharodon carcharias 的隐秘营养生态学

资源利用的人口差异是整个动物界种群和物种生态的关键组成部分。白鲨（Carcharodon carcharias）是迁徙性的顶级掠食者，其分布范围内的种群数量已大幅下降。了解其生态是确保管理策略有效的关键。在这里，我们对南非自由游动的白鲨进行了首次稳定同位素分析。2015 年 2 月至 7 月期间，在干斯拜（南纬 34.5805°，东经 19.3518°）采集活检。我们使用 R 中的稳定同位素贝叶斯省略和传统统计分析来量化和比较两种体型的雄性和雌性鲨鱼的同位素生态位，并分析同位素值与鲨鱼长度之间的关系。我们的结果揭示了性别和生命阶段之间隐秘的营养差异。据推断，随着体型的增大，雄性（而不是雌性）会在更多的近海或西风栖息地觅食，并且只有雄性表现出个体发育生态位转移的证据。δ13​​C、δ15N 与雌性鲨鱼长度之间缺乏关系可能是由于雌性鲨鱼表现出多种迁徙和觅食策略，并且更倾向于向北移动。< 3 m 的鲨鱼比 > 3 m 的鲨鱼拥有更宽、更多样化的生态位，其驱动因素可能包括个体饮食专门化和时间因素。性别、生命阶段和个体之间的迁徙和觅食行为的差异将影响它们对人为威胁的暴露程度，应在管理策略中予以考虑。