Temperature directly and indirectly controls biophysical, biochemical, and bioenergetic processes and is the primary abiotic factor that influences ectotherms via their spatial distributions and daily and long-term survival. Here we examine temperature effects on the survival of multiple life stages of Chinook salmon (Oncorhynchus tshawytscha), a species of high economic importance. Habitat degradation and alteration, hydropower development, and climate change have resulted in recent changes to thermal regimes in salmonid freshwater habitat and corresponding declines in many populations. We implement a framework that provides a quantitative approach for assessing incremental changes in temperature on survival across runs and life stages using the best thermal performance models currently available for Chinook. These temperature-dependent models were combined with local spatial distribution and phenology data to translate spatial-temporal stream temperature data into maps of life stage-specific physiological performance in space and time. Specifically, we convert temperature-dependent performance (i.e. energy used by adults during holding, mortality of eggs during incubation, and juvenile growth rate) into a common currency that measures survival in order to compare thermal effects across life stages.
Results/Conclusions
Preliminary results based on two years of temperature data for three managed rivers in the Central Valley, California, revealed that temperature-dependent mortality during holding was more limiting than embryonic mortality or juvenile mortality prior to smolting. We also found that threatened Central Valley spring-run Chinook were more thermally vulnerable than fall-run. To increase Chinook population sizes, especially for the threatened and declining spring-run, our results indicate that adults may need more cold-water holding habitat than currently available in order to reduce pre-spawning mortality stemming from high temperatures. Future work includes expanding our analyses to include additional years as well as more rivers hosting other populations. To conclude, our framework is an effective way to calculate thermal impacts on multiple salmonid runs and life stages within a river over time, providing local managers the information to minimize negative thermal impacts on salmonid populations, particularly important during years when cold-water resources are scarce.