Cramer Fish Sciences: Yakima O. mykiss Life-History Response Modeling

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CONTACT INFO Ian Courter Cramer Fish Sciences 600 NW Fariss Rd. Gresham, OR 97030 (503) 491-9577 PHONE (503) 465-1940 FAX Header photo courtesy Frank Thrower		PROJECT DESCRIPTION Rainbow-Steelhead Population Viability: Anadromous and Resident Life-History Response in Oncorhynchus mykiss In most Oncorhynchus mykiss populations, the resident (rainbow trout) and anadromous (steelhead) adults interbreed and are capable of producing offspring of the alternate ecotype. Cramer Fish Sciences (CFS) is currently working to model drivers of anadromous and non-anadromous O. mykiss abundance in the Yakima Basin. The goal is to synthesize recent, rapidly advancing research related to life-history variability in partially migratory fish populations, and apply this new body of knowledge to O. mykiss. Results from the project will be used to refine a method of quantifying steelhead viability. Leading up to this modeling effort, CFS conducted a status review of Middle Columbia River (MCR) Steelhead on behalf of the Yakima Basin Joint Board (irrigation districts). Analyses developed by CFS on Yakima steelhead populations were later used by the Bureau of Reclamation to assemble the MCR Steelhead Effects Analysis portion of the Yakima Basin Biological Assessment (BA). Findings from the current modeling project will be used to update the BA. CFS assembled a stochastic population model similar to the analytical tool used by NOAA Fisheries' Technical Recovery Teams to estimate extinction risk probability of endangered and threatened salmon and steelhead populations. The primary difference between the NOAA and CFS approaches is that CFS has incorporated an option to estimate the recruitment exchange between resident and anadromous O. mykiss spawners. The precise magnitude of exchange between the two ecotypes is unknown, but sensitivity analysis revealed the importance of accounting for anadromous recruits derived from resident spawners when calculating extinction risk probability (Figure 1). To refine the stochastic population model parameters, CFS is working together with scientists from NOAA Fisheries, the Yakama Nation, The Joint Board, the Bureau of Reclamation, and the Washington Department of Fish and Wildlife to construct a mechanistic model that will track population response to genetic selection and influence of the environment on abundance of anadromous and resident O. mykiss in the Yakima Basin. Both the population model and the mechanistic model will be applicable to other basins, and available for use as ESA consultation and restoration planning tools throughout California, Oregon, Washington and Idaho.