Game fish response to dredging of a eutrophic urban lake in Minnesota

Abstract Mundahl ND, Hoisington J. 2020. Game fish response to dredging of a eutrophic urban lake in Minnesota. Lake Reserv Manage. 37:170–185. We compared relative abundances, average weights, and growth rates of 6 game fish species before and after the 1999–2001 partial dredging of Lake Winona, a eutrophic, urban lake in Minnesota, to determine whether lake dredging sustainably changed fish population structure to the benefit of anglers. Relative catch rates (trap nets, gill nets, electrofishing) and growth rates were obtained from various fish population assessments and lake surveys conducted by the Minnesota Department of Natural Resources (MN DNR) from 1980 to 2016 for both Lake Winona and Lake Oscar, an ecologically similar lake that has not been dredged. Before-after control-impact (BACI) analyses revealed that compared to Lake Oscar, relative catch rates in Lake Winona after dredging declined significantly for bluegill (Lepomis macrochirus), black crappie (Pomoxis nigromaculatus), and northern pike (Esox lucius), and increased significantly for walleye (Sander vitreus) and largemouth bass (Micropterus salmoides). Average weights of yellow perch (Perca flavescens) and pike increased significantly after dredging. Only black crappie displayed improved growth after dredging. Largemouth bass catch rates for quality- and preferred-size fish increased in postdredging surveys. Although predredging data are lacking, population size structures and relative weights of bluegill, crappie, and bass post dredging were within ranges that meet MN DNR management objectives. Overall, dredging of Lake Winona was followed by improved quality and structure of game fish populations in this system, something that decades of previous biomanipulation and macrophyte management had not accomplished.