Ranking Site Vulnerability to Increasing Temperatures in Southern Appalachian Brook Trout Streams in Virginia: An Exposure-Sensitivity Approach

Models based on simple air temperature–water temperature relationships have been useful in highlighting potential threats to coldwater-dependent species such as Brook Trout Salvelinus fontinalis by predicting major losses of habitat and substantial reductions in geographic distribution. However, spatial variability in the relationship between changes in air temperature to changes in water temperature complicates predictions. We directly measured paired summer air and water temperatures over 2 years in a stratified representative sample of watersheds (<1–274 km2) supporting wild Brook Trout throughout Virginia near the southern edge of the species distribution. We used the temperature data to rank streams in terms of two important components of habitat vulnerability: sensitivity (predicted change in water temperature per unit increase in air temperature) and exposure (predicted frequency, magnitude, and duration of threshold water temperatures). Across all sites, sensitivity was substantially lower (median sensitivity = 0.35◦C) than the 0.80◦C assumed in some previous models. Median sensitivity across all sites did not differ between the 2 years *Corresponding author: [email protected] 1Present address: U.S. Geological Survey, 12201 Sunrise Valley Drive, Reston, Virginia 20192, USA. Color versions of one or more of the figures in this article can be found online at www.tandfonline.com/utaf. Received September 2, 2011; accepted August 9, 2013