SOLON - As the calendar turns to February, some farm ponds and small lakes are beginning to show signs of winter stress and with another blanket of snow covering the state a near certainty, anglers will likely start seeing dead or dying fish under the ice before the spring thaw.
Lakes and rivers that contain gizzard shad see winter die-offs that can look devastating, but these are a natural occurrence in the shad life cycle. Gizzard shad are prolific at spawning and the population will quickly recover in the spring.
"We lose fish every year during the winter, but rarely would that loss rise to the level of a complete fish kill, even during the most severe winter," said Paul Sleeper, fisheries biologist with the Iowa Department of Natural Resources at Lake Macbride.
When frozen lakes are covered by a blanket of snow, it shuts off the sunlight from reaching aquatic plants, which stops photosynthesis and the flow of oxygen into the water. The longer the ice and snow cover the lake, the less oxygen is in the water and available to the fish. Low oxygen levels affect the bottom dwelling and larger fish first and rarely affect all of the smaller fish.
"Pond owners can easily survey their ponds for themselves by spending some time fishing and record what they are catching. We can use that information to offer guidance on pond management," he said. "Usually the best course of action is to allow the pond to recover with the remaining fish filling the void."