The St. Louis River estuary is a designated area of concern by the U.S. Environmental Protection Agency due to severe environmental degradation. The spatial ecology of Muskellunge Esox masquinongy, an indicator species, is uncertain within the estuary and the large, connected water body, Lake Superior. We collected genetic samples and used passive acoustic telemetry to track 60 adult Muskellunge in the St. Louis River estuary and southwestern Lake Superior for 15 months. Genetic analysis revealed that the river is utilized by two genetic strains-Wisconsin (WI) and Minnesota (MN)-and their hybrids. These genetic strains were previously stocked to restore a nearly extirpated population. Muskellunge tended to move upstream in the spring, downstream and into Lake Superior throughout summer, and to the middle river during fall and winter. Males and females spent significantly more time in the upper and lower portions of the river, respectively. Movements were influenced by strain in that hybrids and the WI strain spent more time in the upper and middle river, and the MN strain spent more time in Lake Superior. A random forest model indicated that Lake Superior use was related to strain (the MN strain made up 80% of individuals using Lake Superior) but not sex or body length, highlighting the importance of understanding strain behavior when stocking different strains. Future research should include investigating Muskellunge habitat use (before, during, and after restoration), tracking juvenile Muskellunge, and connecting telemetry data with mark-recapture and stable isotope data. Our results provide new insight into Muskellunge spatial ecology and genetics that can inform management and restoration efforts within and beyond the Great Lakes.

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