• Open Access

State-dependent life history models in a changing (and regulated) environment: steelhead in the California Central Valley

Authors

  • William. H. Satterthwaite,

    1.  Center for Stock Assessment Research, Department of Applied Mathematics and Statistics, University of California Santa Cruz, Santa Cruz, CA, USA
    2.  MRAG Americas, Capitola, CA, USA
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  • Michael P. Beakes,

    1.  Center for Stock Assessment Research, Department of Applied Mathematics and Statistics, University of California Santa Cruz, Santa Cruz, CA, USA
    2.  National Marine Fisheries Service, Santa Cruz, CA, USA
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  • Erin M. Collins,

    1.  California Department of Fish and Game, Sacramento, CA, USA
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  • David R. Swank,

    1.  Center for Stock Assessment Research, Department of Applied Mathematics and Statistics, University of California Santa Cruz, Santa Cruz, CA, USA
    2.  National Marine Fisheries Service, Santa Cruz, CA, USA
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  • Joseph E. Merz,

    1.  Cramer Fish Sciences, Auburn, CA, USA
    2.  Institute of Marine Sciences, University of California Santa Cruz, Santa Cruz, CA, USA
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  • Robert G. Titus,

    1.  California Department of Fish and Game, Sacramento, CA, USA
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  • Susan M. Sogard,

    1.  National Marine Fisheries Service, Santa Cruz, CA, USA
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  • Marc Mangel

    1.  Center for Stock Assessment Research, Department of Applied Mathematics and Statistics, University of California Santa Cruz, Santa Cruz, CA, USA
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William H. Satterthwaite, Center for Stock Assessment Research, Department of Applied Mathematics and Statistics, University of California Santa Cruz, Santa Cruz, CA 95064, USA. Tel.: +1 831 430 6343; fax: +1 831 459 4482; e-mail: satterth@darwin.ucsc.edu

Abstract

We use a state dependent life history model to predict the life history strategies of female steelhead trout (Oncorhynchus mykiss) in altered environments. As a case study of a broadly applicable approach, we applied this model to the American and Mokelumne Rivers in central California, where steelhead are listed as threatened. Both rivers have been drastically altered, with highly regulated flows and translocations that may have diluted local adaptation. Nevertheless, evolutionary optimization models could successfully predict the life history displayed by fish on the American River (all anadromous, with young smolts) and on the Mokelumne River (a mix of anadromy and residency). The similar fitness of the two strategies for the Mokelumne suggested that a mixed strategy could be favored in a variable environment. We advance the management utility of this framework by explicitly modeling growth as a function of environmental conditions and using sensitivity analyses to predict likely evolutionary endpoints under changed environments. We conclude that the greatest management concern with respect to preserving anadromy is reduced survival of emigrating smolts, although large changes in freshwater survival or growth rates are potentially also important. We also demonstrate the importance of considering asymptotic size along with maximum growth rate.

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