Q: Once a lake gets winterkill, how do the fish repopulate? Will they repopulate without DNR stocking?
A: Winterkill is a natural process that happens with some regularity in the southern part of the state due to the type of lakes in the area. From the southern Minnesota lakes perspective, winterkill would be more appropriately termed “partial winterkill.” The Windom fisheries office has rarely seen a complete winterkill, meaning that all fish are dead in a lake. Often, a partial winterkill reduces a large portion of the population, but it varies greatly on the year, lake and fish community.
Black bullhead is a species of fish that has a tendency to survive most winterkill scenarios. Many times the general public sees large numbers of dead common carp and would describe the lake as “dead.” But ice out netting the spring after these winterkill events often reveals many species of fish are alive and well. In spite of the reduction of some of the fish populations, those surviving fish become the brood stock for the population to rebuild. In southern Minnesota, fish can quickly repopulate a lake following a winterkill naturally due to other connected bodies of water that haven’t experienced winterkill.
If a body of water does experience winterkill, then DNR fisheries can do an ice out netting survey to identify species that are present or absent. If the lake is managed for yellow perch and ice out netting reveals an absence of yellow perch and the lake has limited connected sources, DNR fisheries can stock pre-spawn adult yellow perch to reintroduce that species. Those fish then reproduce in the lake naturally.
In southern Minnesota, winter aeration is sometimes used in an effort to prevent partial winterkills but results with that strategy can vary.
-Ryan Doorenbos, Windom area fisheries supervisor