MARQUETTE – The Michigan Department of Natural Resources recently issued its spring advisory, reminding the public it may be common to find dead fish, turtles and frogs or other aquatic creatures as the winter snow and ice abates.
DNR officials said this winter’s more severe conditions, with heavy snow and ice cover, will create conditions that cause fish and other creatures, including turtles, toads, frogs and crayfish to die.
“Winterkill is the most common type of fish kill,” Gary Whelan, DNR fish production manager said in a recent statement. “Given the harsh conditions this winter with thick ice and deep snow cover, it will be particularly common in shallow lakes and streams and ponds. These kills are localized and typically do not affect the overall health of the fish populations or fishing quality.”
Whelan said winterkill occurs during especially long, harsh winters and that shallow lakes with excess aquatic vegetation and mucky bottoms are particularly prone to the problem.
Fish and other aquatic life typically die in late winter, but may not be noticed until a month after the ice leaves the lake because the dead creatures are temporarily preserved by the cold water.
“Winterkill begins with distressed fish gasping for air at holes in the ice and often ends with large numbers of dead fish that bloat as the water warms in early spring,” Whelan said. “Dead fish and other aquatic life may appear fuzzy because of secondary infection by fungus, but the fungus was not the cause of death. The fish actually suffocated from a lack of dissolved oxygen from decaying plants and other dead aquatic animals under the ice.”
Whelan said dissolved oxygen is required by fish and all other forms of aquatic life. Once daylight is greatly reduced by thick ice and deep snow cover, aquatic plants stop producing oxygen and many die. The bacteria that decompose organic materials on the bottom of the lake use the remaining oxygen in the water. Once the oxygen is reduced and other aquatic animals die and start decomposing, the rate that oxygen is used for decomposition is additionally increased and dissolved oxygen levels in the water decrease even more leading to increasing winterkill, Whelan said.
For more information on fish kills in Michigan, visit www.michigan. gov/fishing.
DNR officials asked anyone who suspects a fish kill is caused by non-natural causes, to call their nearest DNR office or Michigan’s Pollution Emergency Alert System at 1-800-292-4706.
John Pepin can be reached at 906-228-2500, ext. 206.