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Fish kills likely in areas of the state

Posted on March 28, 2013

Glenwood, Minn. — During Minnesota’s 2013 version of March, winter seems to have failed to yield to spring, no matter what the calendar says. That might be hard on some of the fish of the state, particularly those in shallow lakes and ponds in the southern half.

Depending on what you’re rooting for, winterkill of fish can be either good or bad. Usually, it’s somewhere in between. While an extreme winterkill can reduce game fish numbers in some situations, winterkill in walleye-rearing ponds can enhance conditions there, resulting in better production during the summer.

Most lakes in his work area were in good condition – oxygen-wise – a few weeks ago, according to Dean Beck, DNR area fisheries supervisor in Glenwood. However, melt and runoff and other things that typically serve to rejuvenate lake water in the spring haven’t happened yet. And now, there are some lakes “I am very worried about,” he said.

Heavy snow during the month – the snowpack on the ice remained about a foot earlier this week – and upwards of 30 inches of ice yet made Beck think things favorable to fish might not be just around the proverbial corner.

Beck noted one area lake in particular that might be suffering the effects of depleted oxygen – the extremely shallow (maximum depth, 8 feet) Lake Emily, located southwest of Glenwood. That’s a lake with a good walleye population, and one that DNR fisheries biologists might investigate for winterkill after ice-out.

“We’d like to get walleye fry in there as soon as possible (if there’s winterkill),” Beck said. “We’ll know fairly soon what we’ve lost.”

In the Ortonville area, DNR fisheries specialist Kyle Anderson said lakes – and fish – are generally in good shape, though a certain amount of winterkill is possible. The area is home to about 40 walleye-rearing ponds, and almost all of those will have some degree of winterkill, he said.

Some, Anderson said, will have “pretty substantial kills, which should be a good thing for walleye production in the fall.”

Besides a cold March and lingering snow and ice, he said the fact that most ponds had low water levels entering winter also likely added to reduced oxygen and dead fish.

Winterkill in ponds is good for a couple reasons, according to Anderson. First, there’s less predation on walleye fry by older fish species – anything from “carryover” walleyes to bullheads – when fry are placed in the ponds. Also, dead, decaying fish from the winter tend to boost the production of invertebrates, on which young walleyes and minnows – future walleye prey – may feed.

There are plenty of factors that contribute to good walleye production in the ponds, and of the 40 in the area, typically around six of those will “hit” in any given year, he said.

Winterkill ups the odds that more will be successful.

Plenty of ice remained on lakes in the Ortonville area earlier this week. Anderson said a lot of locations had ice cover in the upper 20-inch range.

Big Stone Lake has been monitored by the state since 1951, and the average ice-out date is April 9. But an about-face in the weather will be needed to make average this year,

Anderson said: Just last week, ice was still being made due to low temperatures.

The Minnesota-South Dakota border waters game fishing opener (Big Stone is a part of that) is April 20 this year.

Far southwestern Minnesota had ice, but little snow earlier this week. Ryan Doorenbos, DNR Fisheries supervisor in Windom, called it “rock-solid” ice, not yet in the process of decay. And, he added, there was a good 20 inches of it in most places.

Because snow was limited in that corner of the state most of the winter, sunlight penetrated lake ice, and low oxygen appears not to have been a problem for fish species, he said.

However, with little snow, there won’t be any snowmelt to refill some of the lakes and creeks that currently are far below average levels.

Gene Jeseritz, DNR fisheries assistant supervisor in Hutchinson, is one of those hoping spring-like weather arrives – and stays. A couple lakes in that area – including Round Lake near Litchfield – are nearing the point where winterkill could become a factor, he said.

“We’ve found some lakes that are starting to get low (in terms of oxygen levels),” he said. “Winter is getting long.”

But warmer weather was in the forecast, and Jeseritz said it was expected the better fishing lakes in the area would be OK. Snowmelt running into lakes helps reoxygenate the water. But it likely will be a while before the ice is gone.

“Things should’ve been breaking up a bit (by now),” Jeseritz said Monday. “There’s still 28 inches (average) of ice in this area.”

Only one lake in the Hutchinson area was opened to liberalized fishing this year. That was Arvilla in Meeker County. It was opened Jan. 15 and closed Feb. 24. Lakes are opened to liberalized fishing when a fish population is endangered due to the lack of oxygen available in the water.

Jeseritz said the department decided not to open any others this late in the winter season, in part due to the chance that ice conditions could worsen in short order. Now, officials hope water conditions improve for fish.

“Now we’re just hoping for warm weather,” he said.