title: State-dependent life history models in a changing (and regulated) environment: steelhead in the California Central Valley.
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.
authors.affiliation: Center for Stock Assessment Research, Department of Applied Mathematics and Statistics, University of California Santa Cruz Santa Cruz, CA, USA ; MRAG Americas Capitola, CA, USA.
authors.forename: William H
authors.initials: WH
authors.lastname: Satterthwaite
authors.affiliation: Center for Stock Assessment Research, Department of Applied Mathematics and Statistics, University of California Santa Cruz Santa Cruz, CA, USA ; National Marine Fisheries Service Santa Cruz, CA, USA.
authors.forename: Michael P
authors.initials: MP
authors.lastname: Beakes
authors.affiliation: California Department of Fish and Game Sacramento, CA, USA.
authors.forename: Erin M
authors.initials: EM
authors.lastname: Collins
authors.affiliation: Center for Stock Assessment Research, Department of Applied Mathematics and Statistics, University of California Santa Cruz Santa Cruz, CA, USA ; National Marine Fisheries Service Santa Cruz, CA, USA.
authors.forename: David R
authors.initials: DR
authors.lastname: Swank
authors.affiliation: Cramer Fish Sciences Auburn, CA, USA ; Institute of Marine Sciences, University of California Santa Cruz Santa Cruz, CA, USA.
authors.forename: Joseph E
authors.initials: JE
authors.lastname: Merz
authors.affiliation: California Department of Fish and Game Sacramento, CA, USA.
authors.forename: Robert G
authors.initials: RG
authors.lastname: Titus
authors.affiliation: National Marine Fisheries Service Santa Cruz, CA, USA.
authors.forename: Susan M
authors.initials: SM
authors.lastname: Sogard
authors.affiliation: Center for Stock Assessment Research, Department of Applied Mathematics and Statistics, University of California Santa Cruz Santa Cruz, CA, USA.
authors.forename: Marc
authors.initials: M
authors.lastname: Mangel
keywords: adaptation; anadromy; life history evolution; phenotypic plasticity; state-dependent model; steelhead; water management