Common Carp (Cyprinus carpio) Reinvasion and Population Expansion in Lake Winona: A Modified Urban Floodplain Lake in Minnesota, USA

Common or European carp (Cyprinus carpio) were eliminated from Lake Winona during a 1973 lake reclamation project. Multiple efforts to prevent their return and eliminate spawning opportunities have failed. Carp have remained in the lake for the past 50 years, but more recent observations of spawning activity in the lake suggest that their numbers have increased. We used shoreline electrofishing data from Lake Winona (2005–2021), along with carp abundance and effects models, to estimate the abundance of carp in Lake Winona, and to evaluate the need for future carp management within the lake. Carp size (mean TL = 614 mm, mean weight = 3.42 kg) did not differ between eastern and western basins, but densities were three times higher in the western basin (105 compared to 34 fish/hectare), and carp had significantly higher relative weights in the western (117%) versus the eastern (107%) basin. Carp biomass estimates for the eastern (116 kg/hectare) and western (360 kg/hectare) basins suggest that the lake may soon experience significant declines in macrophyte cover and other ecological damage associated with that loss. With an estimated adult carp population of >6900 fish and a carp biomass (23,750 kg) 1.5 times greater than the biomass of all carp killed during the 1973 reclamation, carp management activities (e.g., fish removal and spawning migration barriers) should be initiated soon to protect the Lake Winona game fish community.