Fish Kills Could Be Worse This Year

By Bob Lamb, La Crosse Tribune, Wis.

Mar. 20–The annual dead-fish odor is going to be worse this spring.

David Heath, Wisconsin Department of Natural Resources Mississippi River fish biologist in La Crosse, said the snowier winter will yield more fish kills than in the past. “We’re anticipating that as soon as the ice goes out or is going out, people will see more fish kills than normal, at least in the last 10 years, because of the mild winters we had,” he said. “We had lots of ice and snow this winter, which blocks light from getting to the algae and rooted plants, and hence, there was far less oxygen production in these backwaters.”

Heath said the DNR has discovered instances of very low dissolved oxygen or no dissolved oxygen in some backwater areas this winter.

Fish such as gizzard shad, bluegills, crappies, bass and perch that spend the winter in backwater areas will make up most of the fish kills this spring, Heath said, adding northern pike could be vulnerable as well.

Walleyes, sauger, catfish, shovelnose sturgeon and lake sturgeon — those species that winter in the main channel of the Mississippi River — shouldn’t be affected, Heath said.

“We shouldn’t see any kills in the main channel, hopefully, because oxygen always stays high all winter long,” he said.

Gizzard shad kills are common each spring because these bait fish can’t survive cold water temperatures. However, the lower oxygen production this winter could mean a larger die-off, Heath said.

Some areas to expect fish kills are the Lauderdale Bays, the Black River near the Interstate 90 bridge, French Lake and the upper stretch of Brice Prairie channel from Blackdeer’s cut and beyond, Heath said, adding that kills may occur up and down the backwaters of the Mississippi.

The dead fish will be visible until they rot and sink to the bottom of the river, which takes about three weeks to a month, said Heath.

“We’ll wait about two weeks and see how extensive the kills are,” he said. “We had one at Cold Springs near Ferryville (Wis.) that was massive, with bluegills, crappies and bass. From what we can surmise, they’ve been dying since last month.”

Heath said dead fish found at Cold Springs were further stressed from a fungus infection and overcrowding.

Heath encourages people to report fish kills to him at (608) 785-9993. However, kills should be 50 or more fish.

A spring virus affecting carp also was detected last April in the bay below the Dresbach Dam on the Mississippi River.

“We saw about 1,000 sick carp, but very few dead,” Heath said. “It’s a spring virus that will hit mostly carp.”

Tribune outdoors editor Bob Lamb can be reached at (608) 791-8228 or blamb@lacrossetribune.com.

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