Juvenile Chinook salmon, Oncorhynchus tshawytscha, growth and diet in riverine habitat engineered to improve conditions for spawning

Authors

  • R. M. Utz,

    1. Bren School of Environmental Science and Management, University of California-Santa Barbara, Santa Barbara, CA, USA
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  • S. C. Zeug,

    1. Department of Ecology, Evolution and Marine Biology, University of California-Santa Barbara, Santa Barbara, CA, USA
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    • Present address: Cramer Fish Sciences, 13300 New Airport Road, Suite 102, Auburn, CA 95602, USA.

  • B. J. Cardinale

    1. Department of Ecology, Evolution and Marine Biology, University of California-Santa Barbara, Santa Barbara, CA, USA
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    • Present address: University of Michigan School of Natural Resources and Environment, 440 Church Street, Ann Arbor, MI 48109, USA.


Ryan Utz, National Ecological Observatory Network, 1685 38th Street Suite 100, Boulder, CO 80301, USA (e-mail: utz.ryan@gmail.com)

Abstract

Abstract  Many habitat enhancement techniques aimed at restoring salmonid populations have not been comprehensively assessed. The growth and diet of juvenile Chinook salmon, Oncorhynchus tshawytscha (Walbaum), rearing in a reach designed to enhance spawning were evaluated to determine how a non-target life stage fared in the engineered habitat. Prior work demonstrated differences in food web structure between restored and unenhanced reaches of the Merced River, thus juvenile salmon feeding dynamics were also hypothesised to vary. Dependent variables were compared among fish collected from within and near the upper boundary of the restored reach and in an unenhanced habitat upstream. Diets, otolith-derived growth and stable isotope-inferred trophic positions were compared. Baetidae mayflies were particularly important prey in the restored reach, while elsewhere individuals exhibited heterogeneous diets. Salmon residing at the bottom of the restored reach exhibited slightly faster growth rates relative to fish collected elsewhere, although stable isotope and diet analyses suggested that they fed at a relatively low trophic position. Specialised Baetis predation and/or abundant interstitial refugia potentially improved rearing conditions in the restored reach. Data suggest that gravel enhancement and channel realignment designed to augment adult spawning habitat may simultaneously support juvenile Chinook salmon despite low invertebrate food resources.

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