Title

Site Specialists, Diet Generalists? Isotopic Variation, Site Fidelity, and Foraging by Loggerhead Turtles in Shark Bay, Western Australia

Document Type

Article

Publication Date

5-7-2012

Publication Title

Marine Ecology Progress Series

Keywords

Stable isotopes, Foraging ecology, Animal-borne video, Individual specialization, Marine turtle

ISSN

0171-8630

Volume

453

First Page

213

Last Page

226

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.

Comments

©Inter-Research 2012

Additional Comments

NSF grant #s: OCE0526065, OCE0745606

DOI

10.3354/meps09637

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Peer Reviewed

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