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Marine Ecology Progress Series

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MEPS 453:213-226 (2012)  -  DOI:

Site specialists, diet generalists? Isotopic variation, site fidelity, and foraging by loggerhead turtles in Shark Bay, Western Australia

Jordan A. Thomson1,*, Michael R. Heithaus1, Derek A. Burkholder1, Jeremy J. Vaudo1, Aaron J. Wirsing2, Lawrence M. Dill3

1Florida International University, School of Environment, Arts and Society, Marine Sciences Program, North Miami, Florida 33181, USA
2School of Environmental and Forest Sciences, University of Washington, Box 352100, Seattle, Washington 98195, USA
3Evolutionary and Behavioural Ecology Research Group, Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada

ABSTRACT: Stable isotope data are useful for inferring foraging and niche variation in marine taxa but can be difficult to interpret, in part because different foraging patterns may result in similar isotopic values. Here, we integrate stable isotope analysis (δ13C and δ15N) with behavioral data to investigate the foraging ecology of loggerhead turtles Caretta caretta on a feeding ground in Shark Bay, Western Australia. Large loggerhead turtles showed little among-individual isotopic variance in skin samples, suggesting similar foraging or habitat use patterns over several months or more. Analysis of loggerhead foraging in video data, and comparison with isotopic variance for sympatric green turtles Chelonia mydas, suggest that low isotopic variance among large loggerheads reflects a similar, highly generalized diet within individuals. Higher isotopic variance among smaller turtles may reflect variation in diet, timing of recruitment to neritic habitat or use of food webs varying along other isotopic gradients. Loggerheads showed strong fidelity to the study site over many years, and individuals recaptured frequently showed remarkable affinity for very small geographic areas, often <5 km2. Thus, a substantial proportion of the Shark Bay loggerhead population comprises site specialists, with larger adults appearing to be diet generalists. Our results also suggest that among-individual isotopic variation found at some loggerhead nesting locations may reflect the isotopic characteristics of preferred migratory or foraging grounds owing to long-term site fidelity and less likely reflects prey specialization by individuals within specific feeding areas.

KEY WORDS: Stable isotopes · Foraging ecology · Animal-borne video · Individual specialization · Marine turtle

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Cite this article as: Thomson JA, Heithaus MR, Burkholder DA, Vaudo JJ, Wirsing AJ, Dill LM (2012) Site specialists, diet generalists? Isotopic variation, site fidelity, and foraging by loggerhead turtles in Shark Bay, Western Australia. Mar Ecol Prog Ser 453:213-226.

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