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Great Lakes Article:

Exotic clams claim a new toehold
Troublesome zebra mussels are found in a Crow Wing County lake.
By John Myers
Duluth News Tribune
10/15/03


The first infestation of exotic zebra mussels in a northern Minnesota inland waterway has been confirmed at Lake Ossawinnamakee in Crow Wing County.

The outbreak was confirmed last week and reported Tuesday by the Minnesota Department of Natural Resources.

Exotic species experts fear the small clams could begin to spread throughout the resort, cabin and fishing waters that are the hallmark of the North Country and the Land of 10,000 Lakes.

Wherever zebra mussels have been found, they have become a costly problem, financially and environmentally. But the impact of zebra mussels on small, inland lake ecosystems isn't fully understood. And their impact on tourism and fishing hasn't been studied here.

Lake Ossawinnamakee is south of the famous Whitefish chain of lakes on the Pine River system, upstream from the Mississippi River.

The infestation, discovered by a boat lift installer, was so thick that DNR scientists are sure the mussels are reproducing in the lake.

"It's bad news. They've jumped a couple hundred miles north into an area where Minnesotans do a lot of recreating," said Gary Montz, DNR aquatic invertebrate biologist. "It's not good news for an area with so many lakes so close together."

During a followup inspection, DNR staff also found mussels in cracks of rocks, along contours of a minnow bucket and other tight areas of boat lifts and docks -- from the shoreline to 18 feet deep.

It's not clear how long the mussels have been in the 644-acre lake or how they got there.

Officials will try to isolate the mussels to keep them from spreading. But that could be difficult, if not impossible.

The larval stage of the zebra mussel can flow freely with currents for several weeks. And adults can attach themselves to boats and hitchhike for miles upstream, even surviving out of water for a time.

"That lake becomes a continuous source now for everything downstream. And boats can move them around," said Jeff Gunderson of the Duluth-based Minnesota Sea Grant program, which has tracked zebra mussels for 15 years. "It's going to take even more effort now to continue to get boaters and anglers to keep from spreading them around."

Public education and law enforcement will play a key role in trying to curb their spread.

Boaters are required to inspect their boats upon leaving a lake and remove any exotic species or weeds. Boaters are asked to dry or disinfect their boats between lakes and to not transport any water, even minnow buckets, from lake to lake.

Boaters across Minnesota also are required to drain water from live wells, bilges and bait buckets before leaving infested waters. The harvest of bait from infested waters is prohibited.

On parts of the Great Lakes, the mussels have covered virtually every smooth surface since they began to take hold in 1988. They have caused the extinction of native mussels, covered fish spawning beds and cost industry and government millions of dollars annually to remove from water intakes, docks and sea walls. Their long-term impact on native fish populations remains to be seen.

More than 180 inland lakes in Michigan are infested with zebra mussels, likely due to recreational boaters moving from the infested Great Lakes to others in the state. A few lakes have been infested for a decade.

"The water usually becomes clearer, which means they are intensively filtering nutrients out of the water. Increased water clarity means more rooted plants, more weeds," said Carol Swinehart of Michigan Sea Grant.

Professor Orlando Sarnelle of Michigan State University has studied the impact on lakes infested with zebra mussels. While they reduce the overall algae, he said they cause more blue-green algae -- up to five times more than normal -- which can be toxic to animals and people.

"The problem is especially bad in clear lakes," he said. "And it's a biodiversity issue with them driving native mussels to extinction."

Sarnelle also noted that zebra mussels in Lake Michigan appear to be eliminating a small shrimp-like organism that is the backbone of the big lake's fishery.

Another researcher is looking at the impact of zebra mussels on the growth rate of panfish.

Lake Ossawinnamakee is only the second inland lake in Minnesota found to be infested with zebra mussels. The first was Zumbro Lake near Rochester, which became infested about three years ago. Both the Mississippi River north to the Twin Cities and the St. Louis River estuary in Duluth-Superior also are infested.

On Zumbro Lake and along the Mississippi River, swimmers, water skiers and hikers have complained of cut feet from zebra mussel shells. Hunters have reported their dogs have cut feet on the sharp little shells.

In the Duluth-Superior harbor, walleye anglers commonly snag sticks, native clams and other objects covered in zebra mussels. But, as in Lake Erie, massive numbers of zebra mussels haven't seemed to adversely affect walleye fishing -- at least not yet.

"You can't say with certainty how they'll affect any one body of water. They surprise you," Montz said.

Any cabin owner or business that draws water from a zebra mussel-infested lake can expect to have problems keeping their intake pipes unclogged, experts say.

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