Winterkill is likely for some area lakes in S MN

[h2ofwlr]

Cross column: Winterkill is likely for some area lakes
By John Cross, The Mankato Free Press
February 16, 2014

Dora Lake in Le Sueur County is dying.

The shallow, 732-acre lake has fallen victim to the winter of 2013-14 and with a severe winterkill imminent because of low oxygen levels, the Minnesota Department of Natural Resources has opened it to liberalized fishing through next Sunday, the day the inland waters fishing season for most gamefish closes.

That means anglers can use use just about means — with the exception of seines, hoop nets, fyke nets or explosives — to catch any species found in that shallow 6-foot-deep lake for personal use, no limits.

Hooks and lines are legal, of course. But so is spearing. Ditto for gill nets.

It has been a long winter and as a result, several other shallow lakes in the region may be poised to suffer winterkill, said Scott Mackenthun, assistant supervisor at the DNR’s Waterville Fisheries Office.

“This has been a tough winter, right up there with historically severe winters like those of 1995-96 and 2000-2001,” he said.

The early ice cover followed by uniform snow cover across the area has meant that many shallow lakes, even those equipped with aeration systems designed to prevent such occurrences, may experience some degree of winterkill.

Winterkill is a phenomenon where dissolved oxygen in the water falls to levels insufficient to support fish and other aquatic creatures, causing them to suffocate.

Typically, it is caused by the shutdown of the photosynthetic process of aquatic vegetation after heavy snow blocks out sunlight for extended periods. The process is exacerbated by the decomposition and decay of dying plants, which further deplete oxygen levels.

Mackenthun likened the process to a check book. “You’ve got credits and debits,” he said. “In the fall when the ice forms, the water is cold and is holding so much more oxygen — you’ve got all those credits.”

“As winter goes along and the light isn’t penetrating through all of the snow, those are the debits. By the time February and March roll around, things can be looking tougher and tougher.”

Several lakes in the area, some with previously healthy fisheries, are likely to suffer at least partial winterkills in coming weeks.

Most notably, Mackenthun said that Albert Lea Lake, which had developed a healthy walleye population, is poised to go. “We told the sportsman’s club there last week that they could turn off the aerators.”

Mackenthun said its average depth — only about six feet — can make such systems ineffective in severe winters such as this one.

“There are a lot of factors, but the big one is lake depth,” he said. “You can have the greatest aeration system in the world, but if you don’t have the depth, it won’t always be effective in severe winters.”

The coming days may determine the fate of those lakes on the edge.

A forecast of warmer weather could create some run-off from adjacent watersheds, with a little water flowing in from farm tiles, could improve the situation.

Mackenthun said that while winterkills over the short-term can be painful as anglers watch their favorite fishing waters die, such occurrences aren’t necessarily all bad.

This winter should ensure that shallow lakes in the area used as rearing ponds for walleye fry — lakes such as Wita and Henry — are purged completely of undesirable species, ensuring better survival for walleye to grow to fingerlings for stocking in other area waters.

(Mackenthun acknowleged that Henry accidently has provided some angling for walleyes in recent years, mostly on fugitive fish that eluded DNR crews’ nets.)

And pointing out that lakes prone to winterkills frequently are boom-bust fisheries anyway, Mackenthun said the results from subsequent restocking of winter-killed lakes can be phenomenal.

“You’re starting out with a clean slate without any competing species,” he said. “Sometimes, a winterkill can be the best thing to happen to a lake.”

John Cross is a Free Press staff writer. Contact him at 344-6376 or by e-mail at jcross@mankatofreepress.com.

[h2ofwlr]

Tolerance to oxygen level varies by species

By John Cross, The Mankato Free Press
Sun Feb 16, 2014

The level at which the various fish species are affected by low oxygen levels in the water varies, according to the Minnesota DNR.

Trout are the first to feel the effects at oxygen levels below 5.0 parts per million. Fish next affected are bluegills and bass, which are moderately sensitive to declining levels of oxygen.

Walleye, yellow perch, northern pike, carp and crappies have been able to survive levels down to about 1.0 ppm for extended periods. The last to go, not surprisingly, are bullheads and fathead minnows.

Mackenthun said there is reason to be concerned once levels fall below 2.0 ppm. He also said that dissolved oxygen levels rarely are uniform across an entire lake and that frequently, refuge areas containing higher levels provide refuge for fish.

To view the most recent oxygen levels gathered by DNR Fisheries on some area lakes to to: http://www.dnr.state.mn.us/areas/fisher ... rkill.html

[Goldfish]

Is the lake worth hitting? Could be fun to spear whatever swims by instead of waiting for northern

Sent from a phancy fone

[h2ofwlr]

No idea, but every region in S Mn has such lakes. I have 2 here in Carver and Scott county the is open to any take. Why didn't they allow it to happen a 1 week sooner on these lakes? Only 10 days is ridiculous.