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Long Winter & Fish Populations

blake

Life Member
From the IDNR:

Long Winter Expected to Affect Fish Populations

SPIRIT LAKE - With each passing day of ice cover, there is a growing likelihood that several Iowa lakes and ponds will experience some level of fish kill, and fisheries biologists across the state are keeping an eye on the oxygen levels in their area lakes, and hoping for an early thaw.

"We lose fish every year during the winter, but this has been a hard winter and we are expecting to see more lakes with some winter mortality, and a few lakes with more extensive winter kills," said Jim Wahl, supervisor for fisheries in northwest Iowa.
He said even during the most severe winter, a complete kill is seldom observed. The fisheries staff has been monitoring lakes and will conduct surveys shortly after ice out to see the extent this winter has had on fish populations, Wahl said. Anglers with underwater cameras have called in reports of seeing dead fish at a few public lakes.

"Our lakes froze tight early and have been under ice in some areas for three and a half months. We are still finding 24 to 28 inches of ice so it will be around for some time. The last time we saw a winter like this was in 2000-2001," he said.

When lakes freeze early and receive a blanket of snow, it effectively 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. Wahl said low oxygen levels have been found in a variety of lakes, from the north to the south.

The DNR has taken steps to prevent winter fish kills from low oxygen by placing aeration systems at lakes with a history of winter kills. Aeration systems keep a section of the lake from freezing allowing some oxygen into the water.

"We expect some fish loss but we just won't know the extent of it until we can get our survey boats on the water and sample lakes that had low winter oxygen readings," Wahl said.

For more information, contact Wahl at 712-336-1840.
 
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