French G C A, Rizzuto S, Stürup M, Inger R, Barker S, van Wyk J H, Towner A V, Hughes W O H
1School of Life Sciences, University of Sussex, Brighton, BN1 9QG UK.
2Department of Botany and Zoology, Stellenbosch University, Merriam Avenue, Stellenbosch, 7600 South Africa.
Mar Biol. 2018;165(6):102. doi: 10.1007/s00227-018-3343-x. Epub 2018 May 17.
Demographic differences in resource use are key components of population and species ecology across the animal kingdom. White sharks () 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 δC, δN 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.
资源利用方面的人口统计学差异是整个动物界种群和物种生态学的关键组成部分。大白鲨（）是洄游性的顶级掠食者，其种群数量在整个分布范围内都经历了显著下降。了解它们的生态对于确保管理策略的有效性至关重要。在此，我们对南非自由游动的大白鲨进行了首次稳定同位素分析。2015年2月至7月期间在甘斯拜（南纬34.5805°，东经19.3518°）采集了活检样本。我们使用R语言中的稳定同位素贝叶斯椭圆法和传统统计分析来量化和比较两个大小类别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。随着体型增大，雄性（而非雌性）被推断在更靠近海洋或偏西的栖息地觅食，并且只有雄性表现出个体发育生态位转移的证据。δC、δN与雌性鲨鱼长度之间缺乏相关性可能是由于雌性表现出多种洄游和觅食策略，以及更倾向于向北更远的地方游动。体长小于3米的鲨鱼比体长大于3米 的鲨鱼具有更广泛、更多样化的生态位，其驱动因素可能包括个体饮食特化和时间因素。性别、生命阶段和个体之间在洄游和觅食行为上的差异将影响它们面临人为威胁的程度，在管理策略中应予以考虑。
