Stable isotope evidence of trophic interactions between introduced brook trout Salvelinus fontinalis and native brown trout Salmo trutta in a mountain stream of south-west France

Authors

  • J. Cucherousset,

    Corresponding author
    1. EcoLab, Laboratoire d’écologie fonctionnelle, UMR 5245 (CNRS-UPS-INPT), Université Paul Sabatier, bât 4R3, 118, route de Narbonne, 31062 Toulouse Cedex 9, France
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  • J. C. Aymes,

    1. EcoLab, Laboratoire d’écologie fonctionnelle, UMR 5245 (CNRS-UPS-INPT), Université Paul Sabatier, bât 4R3, 118, route de Narbonne, 31062 Toulouse Cedex 9, France
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    • Present address: INRA, UMR Ecobiop, Quartier Ibarron, 64310 St Pée sur Nivelle, France.

  • F. Santoul,

    1. EcoLab, Laboratoire d’écologie fonctionnelle, UMR 5245 (CNRS-UPS-INPT), Université Paul Sabatier, bât 4R3, 118, route de Narbonne, 31062 Toulouse Cedex 9, France
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  • R. Céréghino

    1. EcoLab, Laboratoire d’écologie fonctionnelle, UMR 5245 (CNRS-UPS-INPT), Université Paul Sabatier, bât 4R3, 118, route de Narbonne, 31062 Toulouse Cedex 9, France
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*Tel.: +33 561 556 730; fax: +33 561 556 096; email: julien.cucherousset@cict.fr

Abstract

The potential trophic impact of introduced brook trout Salvelinus fontinalis on native brown trout Salmo trutta in a mountain stream (south-west France) was investigated using stable isotope analysis (SIA). The isotopic signatures (δ13C and δ15N) of S. fontinalis were similar regardless of the absence or presence of S. trutta, and SIA mixing models revealed that S. fontinalis diet consisted mainly of terrestrial invertebrates. Conversely, a significant shift in S. trutta isotopic signatures (depletion of 1·6‰δ13C and enrichment of 0·6‰δ15N) was observed in sympatry with S. fontinalis; this may be due to a dietary shift towards terrestrial invertebrates. Contrary to an expected dietary divergence in sympatry, an elevated level of dietary overlap was observed between the non-native and native salmonids when in co-occurrence. This dietary convergence is more likely to be due to behavioural interactions than to variations in food availability or fish displacements.

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