Potential impacts of climate change on brook trout (Salvelinus fontinalis) populations in streams draining the Laurel Hill in Pennsylvania

Abstract

To establish a baseline for assessment of climate change effects on populations of brook trout (Salvelinus fontinalis) in southwestern Pennsylvania, we surveyed a collective of headwater streams for fish population status and the development of annual air and stream temperature profiles. The 20 streams selected, 10 located on each facing slope of an anticlinal fold on the Appalachian Plateau, Laurel Hill, historically supported self-sustaining brook trout populations. In these watersheds, anthropogenic activity was minimal and riparian canopy intact. Three, from each facing slope along with the cool-water receiving stream for the respective tributary network, received riparian air and in-stream temperature data loggers. Data loggers were retrieved after one calendar year and temperature profiles for all eight streams downloaded. From these, we analyzed the air/stream temperature relationship for the calendar year and during the growing season for each headwater stream. Wild brook trout were present in all streams along with mottled sculpins (Cottus bairdi) and occasional representatives of six other species. Streams varied in the number of days experiencing thermal stress for brook trout (>18°C) ranging from a minimum of 0 to a maximum of 67, and the slope of each individual air/in-stream temperature relationship correlated with temporal stress. Local differences in riparian cover and groundwater inputs appear to be responsible for the deviation from climate model predictions and suggest resiliency in these headwater ecosystems. Of more immediate concern is the potential for the interruption of connectivity among tributary networks. Thermal profiles of the cool-water receiving streams revealed air temperature as a strong correlate of in-stream temperature. A warming climate may progressively constrict these avenues of gene flow among resident brook trout tributary populations leading eventually to their genetic isolation.