Influence of Stream Temperature on the Spatial Distribution of Westslope Cutthroat Trout Growth Potential within the Madison River Basin, Montana

Abstract

Stream temperature is an important factor influencing habitat suitability for cutthroat trout Oncorhynchus clarkii, but temperature data from headwater habitats are difficult to obtain. We tested the ability of easily obtained landscape and meteorological data to predict the mean daily temperature measured at 79 sites in tributaries to the Madison River, Montana. We also evaluated stream habitat suitability by using temperature predictions to estimate growth potential for age-0 westslope cutthroat trout O. c. lewisi. A model using mean daily air temperature, elevation, and channel gradient explained approximately 75% of the observed variation in mean daily stream temperatures. Classifications of habitat suitability based on predicted fish growth indicated that the majority (78%) of stream habitat in Madison River tributaries provides suitable or highly suitable habitat for westslope cutthroat trout. However, these higher-quality habitats occur primarily in lower-elevation reaches where westslope cutthroat trout have been displaced by nonnative salmonids. Linking potential fish growth to stream temperature predictions will help managers prioritize conservation efforts for this declining subspecies by predicting habitat suitability at potential reintroduction or population expansion sites.