Climate Driven Changes to Thermal Regimes of Mountain Lake-Stream Networks and Adfluvial Migrations of Cutthroat Trout in the Southern Rocky Mountains

Changing climatic conditions in the southern Rocky Mountains (SRM) are a significant threat to the conservation and management of cold-water fishes. These threats include modification of the physical conditions in mountain aquatic systems through altered thermal and hydrological regimes of lakes and streams. However, the specific changes in lake abiotic characteristics (e.g., surface temperature and timing of ice off) resulting from climate change and the consequences for imperiled native cutthroat trout populations in lakes of the SRM are understudied. We use a combination of field studies and modeling to examine how changes in lake surface temperature are related to life history patterns (i.e., adfluvial movement) of cutthroat trout populations. Initial modeling results from 26 SRM lakes suggest a 0.19°C·decade^-1 increase in mean annual lake surface temperature over the next 70 years. More concerning is the 4.7·decade^-1 increase in ice-free days and 0.42°C·decade^-1 increase in summer mean temperatures through the 2080s. We relate these changes in thermal regimes to continuous observations (via PIT tag technology) of adfluvial movements from two lake-stream cutthroat trout populations. These predicted changes in thermal conditions will have important implications for food-web dynamics in these systems and population dynamics of imperiled native cutthroat trout.