ERI Seminar: Gretchen Hansen

Lake Fisheries Under Thermal Pressure

Freshwater lakes in the Midwestern United States are warming rapidly due to climate change, with direct consequences for fish communities that vary by species' thermal tolerances. Recent modeling integrates long-term monitoring data from natural resource agencies with physiological thresholds to forecast abundance changes for key species across diverse lake types.

Coldwater species such as cisco face the steepest projected losses, with average declines of 85% and extirpation risks averaging 46% by the end of the century under business-as-usual scenarios. Coolwater fish including walleye and northern pike are expected to decrease by 33% and 24% respectively, while warmwater species like bluegill and largemouth bass may see modest gains of 7% and 4%.

These changes carry substantial real-world impacts. Recreational fisheries, particularly walleye angling, underpin regional economies through tourism spending and related businesses. States already report localized declines in walleye recruitment linked to warmer conditions and altered food webs.

Non-obvious angles include high lake-to-lake variation: deeper, northern lakes are most vulnerable to coldwater species loss, while shallower southern ones may transition toward warmwater dominance. This creates tensions between regional averages that mask local extinctions and management priorities—restoration efforts targeting one species may conflict with emerging opportunities for others.

Data-fusion approaches using harmonized datasets and tools like web-based planners aim to guide habitat interventions, but uncertainties persist around extreme events, invasive species interactions, and model assumptions.