Spring-run Chinook salmon (Oncorhynchus tshawytscha) are particularly vulnerable to climate change because adults hold in freshwater for the summer before spawning in autumn. Our objective was to determine the streamflow and temperature thresholds that lead to long-term losses or reductions in spring-run Chinook salmon in a California stream, and to evaluate management options to ameliorate these impacts. Hypothesis 1. Climate induced changes in flow and temperature will lead to critical reductions in the available habitat of spring-run Chinook salmon. Hypothesis 2. The loss/reduction of salmon will reduce the diversity and abundance of biota in the riparian corridor. We used WEAP21, an integrated watershed hydrology, water and irrigation management, and water quality model to simulate potential changes in flow and temperature in response to climate change for Butte Creek, California. WEAP21 outputs were used to drive SALMOD (USGS), a spatially explicit and size/stage structured population dynamics model that predicts the growth, survival, and movement of salmon in freshwater systems. We calibrated SALMOD to adult over-summer mortality and smolt out-migration. We used literature reviews, field surveys, 13C and 15N stable isotope analysis, and an expert panel to assess impacts on wildlife as a result of changes to the salmon marine-derived nutrient subsidy.

Results/Conclusions

We bias-corrected and spatially downscaled data outputs for scenarios A2 (greenhouse gas emissions continue to rise) and B1 (significant reductions in emissions) for the period 2010 – 2099 for the six global circulation models (GCMs) recommended by the California Climate Change Research Center. We ran a preliminary test using A2-GDFLCM2.1 climate data. For the periods 2009-2031, 2034-2064, and 2064-2099, WEAP21 predicted streamflow will be reduced 5, 9, and 25%, and water temperature will increase 1.6, 2.1, and 3.5^oC, respectively, relative to the historic period 1986-2005. SALMOD predicted increased summer thermal-based mortality of adults; in some years, none survived to spawn. SALMOD also predicted reduction in recruitment (out-migrating smolts), caused primarily by decreased adult summer survival, as well as increased in vivo and in vitro thermal-based egg mortality. Salmon were predicted to become extirpated in the next 20-25 years. Next we will run the additional GCM/model combinations. Field studies using motion detector cameras baited with salmon carcasses revealed that many vertebrate species consume salmon. We are currently running stable isotope analyses for selected biota that will enable us to develop a conceptual model of the relative importance of marine-derived nutrients to Butte Creek biota and potential impacts in the absence of salmon.