April 27, 2023 at 11:28 a.m.
Fish kills may be common in spring
Concerned citizens should contact DNR
"Winter kill is the most common type of fish kill," Gary Whelan of the Michigan Department of Natural Resources said in a recent press release. "As the season changes, it can be particularly common in shallow lakes, ponds, streams and canals. These kills are localized and typically do not affect the overall health of the fish populations or fishing quality."
Like Wisconsin, cold winters in Michigan can cause the same winter fish kills as seen in the Northwoods.
When deep snowpack reduces the amount of sunlight penetrating into the water column, this can reduce available sunlight for plants. This means less oxygen is being produced for the fish. Especially in shallow lakes with excess vegetation and soft bottoms, this can create unfavorable conditions for fish, leading to mortality. Not only do dead and dying plants stop producing oxygen, but the decomposition process itself can use up any available oxygen in the water.
Pollution from runoff from roads and lawns, as well as from failing septic systems, make smaller ponds and canals more susceptible to fish kills. Large storm events can exacerbate these issues.
Fish and other aquatic life often die in late winter, long before the ice comes off lakes in the Northwoods. They may not be noticed for a month or longer even after ice has left the lake due to them being preserved in the cold water beneath the ice.
On the other hand, unseasonably warm temperatures in the spring can cause fish mortality as well. When water warms quickly, it can stress fish and, at times, will lead to fish mortality as well. Due to having fewer energy reserves in winter, fish are more easily stressed by conditions of low dissolved oxygen and water temperature swings.
"Winter kill 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," Whelan's press release 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 suffocate from lack of dissolved oxygen from decaying plants and other dead aquatic animals under the ice."
What to do in case of a fish kill:
The Wisconsin Department of Natural Resources (DNR) has some recommendations for those who may experience a fish kill. The agency asks that people take the following steps:
• Note the waterbody, date, fish species, and approximate number of dead/dying fish.
• If you caught a suspicious-looking fish, place the fish in a plastic bag and then in a cooler on ice.
• Contact your local fisheries biologist or call the DNR TIP line - 1-800-TIP-Wisconsin DNR - (800) 847-9367.
• Do not bring potentially diseased fish to DNR service stations or hatcheries.
• Do not collect fish samples from a fish kill.
• The local fisheries biologist will contact you as soon as they are available and will make the determination about whether the fish should be examined or not.
• We are encouraging anglers to retain suspicious-looking fish as part of their daily bag limit for examination by the local fisheries biologist.
• The DNR is limited by staff time, financial resources, and laboratory capacity for VHS testing. Therefore, we must prioritize which fish/fish kills we examine in order to ensure that the most likely cases are examined and tested before the less likely ones. Our staff will not have time to visit every occurrence of dead fish or examine every potentially diseased caught fish.
For more information, see the DNR website dnr.wi.gov and search "Winter fish kills."
Beckie Gaskill may be reached via email at [email protected].
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