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Sex, size and isotopes: cryptic trophic ecology of an apex predator, the white shark Carcharodon carcharias.

French, G.C.A., Rizzuto, S., Stürup, M., Inger, R., Barker, S., van Wyk, J.H., Towner, A.V. and Hughes, W.O.H., 2018. Sex, size and isotopes: cryptic trophic ecology of an apex predator, the white shark Carcharodon carcharias. Marine Biology, 165 (6), 102.

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DOI: 10.1007/s00227-018-3343-x

Abstract

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.

Item Type:Article
ISSN:0025-3162
Additional Information:Funding was provided by the National Geographic Society, the Royal Society, and University of Sussex. Samples were collected under permit from Cape Nature (Permit number 0056-AAA041-00078) and the Department of Environmental Affairs (Permit number RES2014/116). Samples were exported from South Africa under CITES Permit 144639 issued by Cape Nature and imported into the UK under CITES Permit 534011/01, issued by the Wildlife Licensing and Registration Service.
Group:Faculty of Science & Technology
ID Code:34256
Deposited By: Unnamed user with email symplectic@symplectic
Deposited On:08 Jul 2020 11:31
Last Modified:08 Jul 2020 11:31

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