Continuous variation in the pattern of marine v. freshwater foraging in brown trout Salmo trutta L. from Loch Lomond, Scotland

Authors

  • E. C. Etheridge,

    1. * Scottish Centre for Ecology and the Natural Environment, Institute of Biomedical and Life Sciences, Glasgow University, Rowardennan, Glasgow G63 0AW, U.K., Department of Physiological Ecology, Max Planck Institute for Limnology, 24306 Plön, Germany and § Scottish Natural Heritage, Caspian House, Clydebank Business Park, Clydebank, Glasgow G81 2NR, U.K.
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  • C. Harrod,

    1. * Scottish Centre for Ecology and the Natural Environment, Institute of Biomedical and Life Sciences, Glasgow University, Rowardennan, Glasgow G63 0AW, U.K., Department of Physiological Ecology, Max Planck Institute for Limnology, 24306 Plön, Germany and § Scottish Natural Heritage, Caspian House, Clydebank Business Park, Clydebank, Glasgow G81 2NR, U.K.
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    • Present address: Queen’s University Belfast, School of Biological Sciences, Medical Biology Centre, 97 Lisburn Road, Belfast BT9 7BL, U.K.

  • C. Bean,

    1. * Scottish Centre for Ecology and the Natural Environment, Institute of Biomedical and Life Sciences, Glasgow University, Rowardennan, Glasgow G63 0AW, U.K., Department of Physiological Ecology, Max Planck Institute for Limnology, 24306 Plön, Germany and § Scottish Natural Heritage, Caspian House, Clydebank Business Park, Clydebank, Glasgow G81 2NR, U.K.
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  • C. E. Adams

    Corresponding author
    1. * Scottish Centre for Ecology and the Natural Environment, Institute of Biomedical and Life Sciences, Glasgow University, Rowardennan, Glasgow G63 0AW, U.K., Department of Physiological Ecology, Max Planck Institute for Limnology, 24306 Plön, Germany and § Scottish Natural Heritage, Caspian House, Clydebank Business Park, Clydebank, Glasgow G81 2NR, U.K.
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‖Tel.: +44 1360 870 271; fax: +44 1360 870 381; email: c.adams@bio.gla.ac.uk

Abstract

Carbon stable-isotope analysis showed that individual brown trout Salmo trutta in Loch Lomond adopted strategies intermediate to that of freshwater residency or anadromy, suggesting either repeated movement between freshwater and marine environments, or estuarine residency. Carbon stable-isotope (δ13C) values from Loch Lomond brown trout muscle tissue ranged from those indicative of assimilation of purely freshwater-derived carbon to those reflecting significant utilization of marine-derived carbon. A single isotope, two-source mixing model indicated that, on average, marine C made a 33% contribution to the muscle tissue C of Loch Lomond brown trout. Nitrogen stable isotope, δ15N, but not δ13C was correlated with fork length suggesting that larger fish were feeding at a higher trophic level but that marine feeding was not indicated by larger body size. These results are discussed with reference to migration patterns in other species.

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