Interactive Effects of Water Diversion and Climate Change for Juvenile Chinook Salmon in the Lemhi River Basin (U.S.A.)

The combined effects of water diversion and climate change are a major conservation challenge for freshwater ecosystems. In the Lemhi Basin, Idaho (U.S.A.), water diversion causes changes in streamflow, and climate change will further affect streamflow and temperature. Shifts in streamflow and temperature regimes can affect juvenile salmon growth, movement, and survival. We examined the potential effects of water diversion and climate change on juvenile Chinook salmon (Oncorhynchus tshawytscha), a species listed as threatened under the U.S. Endangered Species Act (ESA). To examine the effects for juvenile survival, we created a model relating 19 years of juvenile survival data to streamflow and temperature and found spring streamflow and summer temperature were good predictors of juvenile survival. We used these models to project juvenile survival for 15 diversion and climate‐change scenarios. Projected survival was 42–58% lower when streamflows were diverted than when streamflows were undiverted. For diverted streamflows, 2040 climate‐change scenarios (ECHO‐G and CGCM3.1 T47) resulted in an additional 11–39% decrease in survival. We also created models relating habitat carrying capacity to streamflow and made projections for diversion and climate‐change scenarios. Habitat carrying capacity estimated for diverted streamflows was 17–58% lower than for undiverted streamflows. Climate‐change scenarios resulted in additional decreases in carrying capacity for the dry (ECHO‐G) climate model. Our results indicate climate change will likely pose an additional stressor that should be considered when evaluating the effects of anthropogenic actions on salmon population status. Thus, this type of analysis will be especially important for evaluating effects of specific actions on a particular species. Efectos Interactivos de la Desviación del Agua y el Cambio Climático en Individuos Juveniles de Salmón Chinook en la Cuenca del Río Lemhi (E.U.A.)