Unwanted fish may be advancing
Written by Green Bay Press-Gazette   
Sunday, 22 February 2009 11:59
Exotic, prolific, potentially dangerous silver carp were found in Wisconsin waters for the first time in 2008 — in the Mississippi River.

Where in the state will they appear this year? Next year and the years' after?

"We need to make sure we have our eyes on the back door as well as the front door," said Robin McLennan, northeast region supervisor for the Wisconsin Department of Natural Resources.

While national attention has riveted on preventing silver carp from migrating up the Chicago shipping canal into Lake Michigan, fisheries biologists in central Wisconsin are concerned the exotic fish is ready to move into the Lower Wisconsin River.

Most people recognize silver carp from video clips showing fish leaping into the air when motor boats pass. The fish, which can reach weights up to 60 pounds, have proven hazardous to some recreational boaters.

Silver carp reportedly entered the United States in the 1970s when they were imported from Asia by catfish farmers to remove unwanted algae and other suspended matter from their ponds. The carp soon found their way into other waters.

"Silver carp showed up in the Mississippi River near La Crosse in the fall of 2008 when commercial fishermen found several in their nets," said McLennan.

The Mississippi is the main funnel for a host of major Wisconsin rivers, including the Wisconsin River, which empties into it downstream of La Crosse at Prairie du Chien in the southwest corner of the state.

That distant connection has McLennan fretting.

"At this point, silver carp have access to the Wisconsin River as far north as the Prairie du Sac dam, the first dam upstream from the Mississippi River," he explained.

"Right now, that dam is a barrier to fish passage but I fear that — one way or another — silver carp will get into the next section of the river" and eventually pose a threat to upstream reservoirs.

Another potential problem exists at Portage, a city that drew its name from early voyageurs who found it easy to transport loads between the Fox and nearby Wisconsin rivers.

While the Wisconsin River watershed encompasses streams and reservoirs throughout the north central section of the state, the Fox River drainage flows into the Lake Winnebago system and ultimately into Green Bay and Lake Michigan.

At one point more than a century ago, a canal to handle boat traffic connected the two rivers at Portage. That canal was subsequently abandoned and today handles barely a trickle of water, according to McLennan.

A system of levies and sand dikes were constructed decades ago to prevent the Wisconsin River from again merging with the Fox.

However, McLennan notes, "Our concern is that during a very large flood event, waters could merge between the two basins," allowing silver carp access to the Lake Winnebago system.

DNR officials, including James "Andy" Morton, basin supervisor for the Lower Wisconsin River, have been working with the Portage community to close possible access points for water spillover.

"We installed a block at an intake canal that connected the Wisconsin and Fox rivers," Morton said. "Our solution is to prevent any kind of transfer between the basins."

The department is also taking steps to ensure a proposed fish passage for sturgeon at the Prairie du Sac dam won also allow silver carp to migrate further upstream.

"My concern with is they are filter feeders," McLennan said. "They run through the water and filter out zooplankton and algae" that form the food basis for the rest of the ecosystem. Once established in a favorable environment, silver carp often become the dominant species.

"The Lake Winnebago system is rich in nutrients and would be ideal for silver carp," McLennan said. "It would provide a smorgasbord for them. There is potential for major ecological consequences."

Lake Michigan, with cooler water temperatures and fewer nutrients, may prove less suitable to silver carp, he added. The warmer waters of Green Bay might be a different matter.

If silver carp expand their foothold in Wisconsin waters, the consequences could have significant monetary as well as ecological impact.

A recent study by University of Wisconsin specialists concluded sport angling in the Lake Winnebago region along generates more than $300 million annually in economic activity.

Lake Michigan is home to recreationally attractive trout and salmon fisheries while Green Bay continues to gain acclaim for its budding muskie, walleye, northern pike, smallmouth bass and perch fishing opportunities.

Decimation of these fisheries would be catastrophic to anglers as well as the businesses catering to them.
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