Life-Cycle Modeling of Columbia River Basin Salmonid Populations -Translating Restoration Actions into Population Viability Metrics

Salmon populations suffer from anthropogenic impacts throughout their life history. Accordingly, recovery plans for threatened and endangered populations typically involve mitigation actions in several life stages. This presents the challenge of assessing how multiple mitigation actions will integrate into cumulative benefits for a population. Incorporating predicted survival improvements into life-cycle models is a useful approach for translating multiple improvements into changes in population viability metrics such as probability of extinction or long-term abundance. We developed stochastic, stage-based life-cycle models of salmon and steelhead populations throughout the interior Columbia River basin. We included climate effects in the freshwater rearing and in early ocean survival and density dependent recruitment of juveniles. We used the models to predict how mitigation actions in freshwater rearing habitats and in the estuary and improvements in the hydropower system will enhance population viability. A great challenge in this type of modeling is the need to translate results from field experiments into parameters in life-cycle models, and we discuss our experiences with this issue. We also address the question of how future climate change scenarios will influence the efficacy of mitigation actions and how populations will respond differentially to climate change. Finally, because life-cycle models are only as strong as the data that support them, we discuss the need to link modeling and monitoring efforts.