Stranding of Spawning Run Green Sturgeon in the Sacramento River: Post Rescue Movements, Population Level Effects, and Management Implications

            The lower portion of the Sacramento River has been highly engineered to protect low lying surrounding communities from annual flood events.   While engineered flood plains have provided adequate protection for the surrounding communities, there remain unintended consequences to migratory fish which become stranded during high flow events.   In April 2011 collaboration between U.C. Davis, state and local federal agencies resulted in the rescue of twenty four stranded ESA listed green sturgeon stranded at flood control diversions. We analyzed post-rescue movements of 24 acoustically tagged green sturgeon to determine survival and continued migration success to the spawning grounds.  Additionally, we provide a population viability analysis to show the potential population level impacts of stranding and the benefits of conducting rescues as a short term management tool.  We found that 17 of 24 individuals continued their upstream migration to the spawning grounds.  Modeling results suggest that stranding in frequencies greater than a single year, without rescue could potentially affect the long term viability of green sturgeon.  Population estimates with rescue predicted a 7% decrease below the population baseline model as opposed to 33% without rescue.   While rescue operations show promise as a short-term management strategy for reducing population level effects of stranding, major fish passage improvements to flood control diversions should be considered as a long term goal to decrease stranding risk at flood diversions in the Sacramento River.