Fish Habitat Models Developed for the Midwest Glacial Lakes Partnership

The mission of the Midwest Glacial Lakes Partnership is to protect, rehabilitate, and enhance sustainable fish habitat in glacial lakes of the Midwest for the use and enjoyment of current and future generations.  A landscape-based assessment of fish habitat condition for all lakes of this region was conducted by Downstream Strategies to help identify appropriate actions and set conservation priorities.  Our partnership delineated lake catchment boundaries and helped to organized a suite of landscape variables, including natural and human influences, for all lakes 25 acres or greater.  Downstream Strategies developed boosted regression tree models to predict presence/absence and relative abundance of walleye, northern pike, bluegill, coldwater fishes, and concentration of summer total phosphorus.  The results of the modeling process were informative.  For both coldwater fish and walleye, the predictor variable with the largest relative influence on probability of presence was log of lake area.  For both bluegill and summer TP, the dominant predictor was local July air temperature.  For northern pike, the dominant predictor was catchment mean sulfate deposition rate.  Future refinements could examine the causative relationships associated with the strong correlations identified in the modeling.