Effects of Climate Change on Thermal Habitat for Native and Nonnative Salmonids: Looking Across Multiple Scales in a Mountain-Valley Stream Network

Understanding the potential effects of climate change on stream thermal regimes has become a fundamental concern for fisheries managers and ecologists. In this study, we assessed the availability of suitable summer stream temperatures for native and nonnative salmonids in a mountain-valley stream network. Stream temperatures were surveyed with a combination of thermal infrared (TIR) imagery, continuous longitudinal temperature profiling, and stationary water temperature loggers. TIR imaging and continuous longitudinal profiling were effective methods for evaluating explicit spatial patterns in temperature data at multiple spatial scales, and fixed temperature loggers enabled an explicit evaluation of temporal variation in stream temperature. Suitable thermal habitat was patchily distributed throughout the study area, and cold-water tributaries likely provide critical cold-water thermal refugia. Present and past thermal data were incorporated into statistical stream temperature models, and future changes in thermal habitat were assessed based on regional climate change predictions. Under scenarios of increasing and more variable summer air temperatures, we predicted a significant increase in the occurrence of stream temperatures that exceed chronic and acute thermal tolerance thresholds for salmonids. Evaluating spatial patterns in predicted stream temperatures allowed us to identify areas critical to maintaining future coldwater habitat.