MPR: Killing Fish to Improve Fishing

Killing Fish to Improve Fishing
By Laurel Druley
Minnesota Public Radio
May 1, 2001

The Minnesota Department of Natural Resources killed hundreds of thousands of fish last winter. They did it on purpose, on a few lakes around the state as an experiment. Their intention, to restock the lakes with what sportsmen call "more desirable" fish.

The DNR purposely killed thousands of rough fish, including carp, in Lake Hanska near New Ulm during the winter. The agency will now restock the lake with game fish such as bass, walleye, and perch.
(Photo courtesy of the DNR)

WHEN YOU DRIVE INTO THE TOWN OF NEW ULM, the marquee at the Lutheran Church reads, "You catch em, God'll clean em." At one time New Ulm and the neighboring town, Hanska, were known as hot fishing spots. And folks like Jim Bruss want the good fishing to return. Bruss says the last few years he's had to travel several miles for the hot bites, even though his home sits on what was once a prime fishing location near New Ulm. Bruss says he'd like to throw a line out his back door again. And the Department of Natural Resources hopes to make that possible.

"I was born and raised on the lake. I've seen it peak and valley over the years, and I know what it's capable of being. It's too good not to share," says Bruss.

The lake he's talking about is Lake Hanska, a 1,700-acre shallow body of water just outside of New Ulm. Farms and roads surrounding the lake have produced runoff that encourages a mucky lake.

Before humans moved in, scientists say Hanska was probably a pristine wetland with a balanced ecosystem. Over the last several years, carp and other bottom feeders have stirred up the sediment, preventing sunlight from hitting the bottom of the lake. Rooted plants such as cattails and bullrushes have died off, while carp, bullheads and other so-called "undesirable" fish have flourished. The poor vegitation also makes for an unappealing habitat for waterfowl, such as geese and ducks.

In January, the DNR began its attempt to reclaim the lake. In the past, the agency has done this with chemicals. But Norm Haukos, a DNR biologist, wanted to try something more economical - a process called reverse aeration. He and his team set up two aerators on top of the ice. The system created a circular current starting at the bottom of the lake, that gradually eliminated oxygen from the water. In a couple of days, hundreds of thousand of fish carcasses floated to the top. Today, a few bloated fish remain near the dam and the stench of rotting fish still lingers.

"We think we have a really good kill out there," says Haukos.

The rough fish kill is good news for waterfowl, game fish enthusiasts and DNR managers. In a couple of months the DNR will restock the lake with walleye, northern pike, largemouth bass, black crappie, bluegill and yellow perch. The whole process will cost almost $10,000.

The fish kill on Hanska wasn't the first. In 1989, a chemical called rotenone was used to wipe out the fish population, at a cost of $150,000. The agency then restocked the lake and anglers were content for a few years - until farm runoff produced more sludge. Bottom feeders moved in and the cycle started all over again. Each winter, hundreds of shallow lakes like Hanska have natural winter kills. But hardy fish like carp tolerate the cold. Haukos says the DNR will have to continue to manage the lake. And this probably won't be the last human-induced fish kill.

Ira Adelman, a professor at the University of Minnesota, wonders if it's appropriate for humans to rectify the damage they've already caused with agricultural development.

"These are very altered systems to begin with, so do you let them continue to exist as they are? Or do you attempt to do something to restore them to a situation where they can be used for recreation, or restore them to a more natural state?" he says.

Adelman notes that one of the DNR's responsibilites according to Minnesota statute is to improve the water for recreational purposes, such as fishing. But Adelman also points out that the DNR chose to restore a different lake, Heron Lake, to a more pristine self-sustaining condition by focusing on the surrounding habitat - not just the lake itself. He can already predict the Heron restoration project will have more lasting effects.

More information:

Minnesota DNR
What does ecosystem-based management mean to Minnesota anglers?
DNR's lake finder site.
Enter "Lake Hanska" in the search box and see where it is on the map.
DNR's Fish and Wildlife Today webzine
An article about the drawdown and rotenone treatment at Lake Hanska in 1998.
The Heron Lake Watershed Restoration Project
The DNR is part of the Heron Lake Watershed Restoration project, which is attempting to restore the entire habitat and ecosystem in and surrounding the lake.

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