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Winter Diets of Immature Green Turtles (Chelonia mydas) on a Northern Feeding Ground: Integrating Stomach Contents and Stable Isotope Analyses

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Abstract

The foraging ecology and diet of the green turtle, Chelonia mydas, remain understudied, particularly in peripheral areas of its distribution. We assessed the diet of an aggregation of juvenile green turtles at the northern edge of its range during winter months using two approaches. Stomach content analyses provide a single time sample, and stable isotope analyses integrate diet over a several-month period. We evaluated diet consistency in prey choice over time by comparing the results of these two approaches. We examined stomach contents from 43 juvenile green turtles that died during cold stunning events in St. Joseph Bay, Florida, in 2008 and 2011. Stomach contents were evaluated for volume, dry mass, percent frequency of occurrence, and index of relative importance of individual diet items. Juvenile green turtles were omnivorous, feeding primarily on seagrasses and tunicates. Diet characterizations from stomach contents differed from those based on stable isotope analyses, indicating the turtles are not feeding consistently during winter months. Evaluation of diets during warm months is needed.

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Acknowledgments

We express our sincere thanks and appreciation to H.J. Brockmann for her creative assistance, support, and advice throughout the research and writing process. We thank L. Avens, B. Stacy, A. Bolten, P. Eliazar, M. Frick, M. Lopez-Castro, M. Pajuelo, J. Pfaller, L. Soares, H. Vander Zanden, and P. Zarate for project and creative assistance. J. Curtis of the Stable Isotope Lab at the University of Florida assisted with stable isotope analyses. We thank S. Farris, M. Pajuelo, and B. Stephens for the collection of stomach contents. We also thank the many volunteers who assisted during the cold stunning events. The Sea Turtle Grants Program (funded from proceeds from the sale of the Florida sea turtle license plate), Knight Vision Foundation, and Jennings Scholarship funded this research. All research was performed under Florida Marine Turtle Permits #016 and #094. Samples were collected and processed in compliance with the Institutional Animal Care and Use Committee at the University of Florida. References to non-USGS products and services are provided for information only and do not constitute endorsement or warranty, expressed or implied, by the US Government, as to their suitability, content, usefulness, functioning, completeness, or accuracy.

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Authors and Affiliations

  1. Department of Wildlife Ecology and Conservation, University of Florida, Gainesville, FL, 32611, USA

    Natalie C. Williams & Raymond R. Carthy

  2. Archie Carr Center for Sea Turtle Research University of Florida, Gainesville, FL, 32611, USA

    Natalie C. Williams, Karen A. Bjorndal, Margaret M. Lamont & Raymond R. Carthy

  3. Department of Biology, University of Florida, Gainesville, FL, 32611, USA

    Karen A. Bjorndal

  4. Florida Cooperative Fish and Wildlife Research Unit, U.S. Geological Survey, Gainesville, FL, 32611, USA

    Margaret M. Lamont & Raymond R. Carthy

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  1. Natalie C. Williams
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  2. Karen A. Bjorndal
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  4. Raymond R. Carthy
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Correspondence to Natalie C. Williams.

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Communicated by Hilary Kennedy

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Williams, N.C., Bjorndal, K.A., Lamont, M.M. et al. Winter Diets of Immature Green Turtles (Chelonia mydas) on a Northern Feeding Ground: Integrating Stomach Contents and Stable Isotope Analyses. Estuaries and Coasts 37, 986–994 (2014). https://doi.org/10.1007/s12237-013-9741-x

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