Assessment of Stressors on Fall-Run Chinook Salmon in Secret Ravine

Assessment of Stressors on Fall-Run Chinook Salmon in Secret Ravine (Placer County, CA)

Group Members Elizabeth Ayres, Eli Knapp, Suzanne Lieberman, Julie Love, Kirk Vodopals

Faculty Advisors Bruce Kendall, Ph.D. and Carol McAusland, Ph.D.

In this study we investigate the impact of anthropogenic stressors on the fall-run Chinook salmon (Oncorhynchus tshawytscha) in Secret Ravine, Placer County, CA through an Ecological Risk Assessment (ERA). The Central Valley fall-run species has experienced exponential decline in the last half-century, and community stakeholders are interested in understanding the causes of this decline. We use the Relative Risk Model as a guide, a specialized form of ecological risk assessment, which was developed by Dr. Wayne Landis of Western Washington University. Our study combines quantitative source analysis of land use through geographic information systems (GIS), with dose-response estimates of biological, chemical and physical stressors to the salmon. Because the Relative Risk Model was designed to rank and prioritize ecosystem effects on a regional scale, we have also created a model which may be better equipped to evaluate stressors at the watershed scale (the "Stressor-Driven Risk Model"). Both models enable use of qualitative input in the absence of complete data because they allow managers to take action based on known prioritization of risk, rather than resorting to a traditional "wait and see" approach or weighting the results strictly against economically feasible solutions.

We analyzed and quantified the risk associated with twelve sources and ten stressors. We used the top three stressors associated with the most highly contributing sources from the results in the Modified Relative Risk Model to analyze effects directly associated with the top stressors in the Stressor-Driven Risk Model. We synthesized the results of both models to be able to more comprehensively characterize the stream system and its impacts on the fish in order to make management recommendations to stakeholders. The risks facing the fall-run Chinook salmon reflect many of the risks that threaten the overall stream health of the larger watershed within Secret Ravine and the Sacramento River drainage system. Therefore, the results of the ERA should serve as a template for future management of fall-run Chinook, as well as management of similar creeks under threat of encroachment by suburbanization.