Bald eagles have become a fixture in Marion County every winter, attracted by a surprisingly plentiful food source.
Every winter, full-grown shad die and float to the surface of lakes in the winter, an easy meal for eagles. Shad are small fish, larger than minnows, commonly eaten by sport fish.
With the easy pickings available, there have been as many as nine eagles sighted at once at the county lake, officials said.
Other species can be vulnerable to a more serious phenomenon called winterkill possibly decimating aquatic ecosystems. This winter hasn’t been severe enough to prompt winterkill in the state, though, a fisheries biologist with Kansas Department of Wildlife, Parks, and Tourism said.
Walter K. Dodds, distinguished professor of biology at Kansas State University, said winterkill primarily happens in lakes that are prone to algae blooms, as the county lake and reservoir have been the past several summers.
When such a lake freezes over, algae can’t get enough sunlight to continue photosynthesis, and they die, Dodds said. It is especially severe if snow then builds up on the ice. As bacteria decompose the dead algae, they use up oxygen that fish need to breathe.
Shad are especially susceptible to winterkill. Additionally, sport fish like bass and bluegill are more susceptible to winterkill than catfish, carp, and drum, which can tolerate lower oxygen levels, Dodds said. When there is a serious winterkill, the surface of a lake can be covered with dead fish.