Resilience of Optimal Thermal Habitat to Climate Change in Wisconsin Lakes

Thermal habitat in lakes is influenced by multiple drivers including air temperature, land use, lake morphometry, and water clarity. Future availability of fish thermal habitat is expected to vary widely among lakes because of variation in these characteristics. Approaches focusing on the “average” lake, or those using air temperature as a surrogate for fish habitat, will mask among-lake variability vital for managing on the landscape scale. We developed a mechanistic model to forecast temperature and oxygen profiles for 2,500 Wisconsin lakes, and projected thermal habitat availability through 2100 for various fish species and life stages. Lakes temperatures responded differently to climate change, even when exposed to similar climactic conditions. Forecasted habitat availability also differed depending on how we defined optimal habitat. For example, lakes differed in forecasted thermal habitat for Walleye (Sander vitreus) depending on the range of temperatures defined as “optimal” (e.g., 22-23 vs. 18.2-28.2⁰ C). Due to uncertainty in the relevant thermal range for projecting future habitat suitability, we identified a subset of lakes projected to maintain Walleye habitat across multiple optimal habitat measures. These lakes are predicted to be the most resilient to future climate, and management to protect Walleye should be prioritized in these systems.