Application of a Riverscape Water Temperature Model for Conservation and Management of Threatened Salmonids in the Pacific Northwest

Water temperature is a key control on growth and survival of fishes and ultimately influences productivity and life-history expression.  Consequently, understanding the natural variation in thermal conditions across broad spatial scales has important implications for conservation and management of threatened stream fishes.  We developed a spatially and temporally explicit stream water temperature model parameterized using empirically-derived water temperature observations and remotely-sensed land surface emissivity. Based upon model-estimated mean and maximum daily water temperatures, we derived metrics to characterize thermal regimes experienced during spawning and early juvenile rearing for two threatened salmonid species: steelhead (Oncorhynchus mykiss) and bull trout (Salvelinus confluentus).  Among covariates representing aspects of the physical environment, cumulative degree days was the most important predictor of the distribution and abundance of steelhead spawning across the John Day river basin, Oregon. For bull trout, we used modeled maximum temperature estimates to delineate habitat patches and develop a habitat suitability index in the Wenatchee River basin, Washington. Subsequently, we modified thermal regimes based on output from a spatially-explicit wildfire model, and estimated potential post-fire vulnerability of critical habitats for bull trout.  These two examples highlight the utility of a continuous view of thermal regimes for stream fish conservation applications.