Muskellunge Spawning Habitat: Site Preferences and Predictive Models for Management

Muskellunge spawning habitat has been identified as critical for preserving naturally reproducing populations. Spawning habitat data were collected on twenty-nine inland lakes in northern Wisconsin. Ivlev’s index of electivity was calculated for each lake, enabling comparisons of habitat preference across lake types. Muskellunge showed a preference to spawn in areas with medium to steep bathymetric slopes, mixed forest, evergreen forest, agricultural riparian land cover, minimal groundwater flow, eastern-facing shorelines, bays, and gravel substrates. Preferences for riparian mixed forest, groundwater recharge, and sandy substrates were shown to differ with the trophic state of the lake according to Carlson’s trophic state index. Two GIS-based spawning habitat models were created using Maxent to predict the locations of spawning habitat: one for eutrophic and mesotrophic lakes and another for oligotrophic lakes. Both models showed moderate performance when discriminating spawning sites from available littoral habitat. For example, when the models identified the best 30% of potential spawning habitat, that area encompassed 55% of spawning sites. The applicability of these models to novel lakes was tested using a k-fold validation procedure that withheld one lake at a time to test the model. Corresponding performance was generally moderate, but variable with lake size and lake habitat quality.