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Great Lakes Article:

Invasive fish moves up Fox River

White perch threaten Lake Winnebago

By Peter Rebhahn
09/18/2002

Exotic species

Exotic species are plants or animals that enter an ecosystem from beyond their native ranges.

Exotics are sometimes called “invasive” species because they tend to take over new habitats. That’s because natural predators aren’t present outside the exotics’ normal range. Native species aren’t adapted to exotics, and lack the ability to compete. The population explosion that results can upset the ecological balance of aquatic or terrestrial habitats. Once established, exotics are nearly impossible to eliminate.

Source: state Department of Natural Resources

For the first time, white perch, an invasive species implicated in the decline of the yellow perch fishery in the Great Lakes and the bay of Green Bay, have been found in the Fox River upstream of the Rapide Croche navigational lock and dam northeast of Kaukauna.

The invasion could spell trouble for fisheries in Lake Winnebago and the Wolf and upper Fox rivers. Both rivers empty into Lake Winnebago.

“There’s nothing that really stops these invasive species,” said Terry Lychwick, a fisheries biologist with the state Department of Natural Resources. “I don’t have any reason to believe they wouldn’t just keep going wherever they could.”

Lychwick said the DNR discovered 11 adult white perch of varying sizes in the pool above the dam in late August. More sampling in the first two weeks of September turned up “young of the year” — tiny white perch that could only have been hatched last spring.

The discovery is certain to add fuel to a debate already raging between state officials, who have endorsed a plan to renovate and reopen 16 of the lower Fox River’s 17 locks to allow unimpeded boat traffic up the river from the bay of Green Bay, and opposing sportsmen’s groups who fear the move will open a Pandora’s box of invasives on Lake Winnebago.

“Just think of the economic impact to the Lake Winnebago system if all these exotic species get into the system and we lose half of our fish out here,” said Jim Schommer, a Fond du Lac resident and president of Walleyes for Tomorrow. “That alone is enough to scare a lot of people.”

It scares Bill McAloon, a past president of the 1,000-member Otter Street Fishing Club in Oshkosh who opposes opening the locks — a step he said will make a tough battle against the invasive species in Lake Michigan and the bay of Green Bay unwinnable.

“I’m sure it’s just a matter of time before everything will be up here,” McAloon said.

Lychwick said inspection of the five locks upstream of Rapide Croche offered little hope they will block passage of white perch upstream to Lake Winnebago.

“They were in pretty bad shape,” Lychwick said, adding that water coursed through several. “As it stands now, there would be a potential.”

Lychwick said biologists believe the lock and sea lamprey barrier at Rapide Croche is sound, and that white perch passed the obstacle with human help — most likely unknowing children or fishermen who broke the law against moving fish between bodies of water.

If fishermen introduced white perch above the dam, they may have believed they were moving white bass, a species that closely resembles white perch, Lychwick said.

“Could it be malicious? Yes, those things happen,” he said.

The $20 million project that would create the Fox River Heritage Parkway would open all the lower river’s locks except Rapide Croche to boat traffic. A lift would move boats over the dam at Rapide Croche. The Menasha-based East Central Wisconsin Regional Planning Commission is charged with creating the plan for the project.

“It really calls into question what type of management policy you should have for exotics,” said Harlan Kiesow, commission executive director.

But Kiesow said the white perch problem is no reason not to move ahead with the project, and pointed out that another invasive, the zebra mussel, is already in Lake Winnebago courtesy of fishermen and recreational boaters who moved their boats from the lake or bay without properly cleaning them.

Lychwick said scientists have linked an explosion of white perch in Lake Erie in the 1970s with reduced numbers of white bass and yellow perch, though there’s less evidence that white perch have hurt walleye populations. The potential exists for white perch to change the Lake Winnebago fishery more significantly and faster than Lake Erie’s because Lake Winnebago is so much smaller.

“Something will happen, but we can’t predict it,” Lychwick said. “Ultimately there will be a change. Probably, it won’t be to the better.”

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