A conditional strategy model accounts for spatiotemporal life-history variation in Snake River fall Chinook salmon

Alex Perkins, University of California, Davis

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This study advances a hypothesis for the mechanism by which juvenile fall Chinook salmon in the Snake River adopt one of two life histories, and it formalizes that hypothesis with a simulation model we used to explain observed patterns of spatial and temporal life-history variation. The model integrated published information about temperature-based growth and survival with daily temperature means to simulate individual growth trajectories commencing on a known distribution of spawning dates. Simulated growth trajectories and daily temperature data allowed us to evaluate a range of threshold trait values to determine which values produced simulated yearling proportions most consistent with those observed by Connor et al. (2002, N. Am. J. Fish. Manag. 22:703). Indeed, best-fit threshold parameters produced simulated proportions consistent with both observation and known temperature differences among river sections and observation years. Furthermore, we determined that best-fit threshold parameters are robust to uncertainty in yearling over-winter survival. This study indicates important directions for future empirical research, and the model offers those interested in the management and conservation of Snake River fall Chinook salmon a useful tool to account for life history variation in population viability analyses.

Abstract Author(s): T. Alex Perkins, Henriette I. Jager, James A. Chandler, Phillip A. Groves