Instream Flow Issues and Climate Change Impacts for Juvenile Chinook Salmon

Managing fish populations in the face of escalating human water demand and climate change is a major challenge for the 21^st century. Water diversion is causing shifts in the quantity and timing of streamflow, and climate change may further impact temperature and flow regimes. Historically, the Lemhi River subbasin in Idaho had a large Chinook salmon population, but the population has experienced substantial declines and is currently listed as threatened. The Lemhi River experiences large-scale water diversion for irrigation and the impacts of this for spring Chinook salmon are not fully understood. We used 15 years of data to model the relationship of flow, temperature, and density on juvenile salmon survival. Spring flow and summer temperature were found to be good predictors of juvenile survival with higher flow and lower temperatures associated with increased survival. We used these models to compare survival between diverted and undiverted scenarios for both current and predicted future conditions under climate change. Water diversion substantially decreased survival due to lowered flow, while climate change scenarios led to further decreases in survival, primarily due to increased temperatures.