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Sorensen

Invasive carp gets an earful from experimental underwater speakers

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GENOA, Wis. — Any invasive carp trying to swim up the Mississippi River through the shipping lock here will get an earful.

Five underwater speakers blare out the racket of roughly 20 outboard motors — a sound unpleasant to humans, unnoticed by native fish, and super-annoying to invasive bighead and silver carp, so much so that they swoosh tail and swim back downstream, researchers hope.

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The “acoustic deterrent system,” designed to slow the upstream rampage of the non-native fish often known as Asian carp, is activated every time the downstream gates of Lock and Dam No. 8 south of La Crosse creak open. The first-of-its kind experimental project — believed to be the largest underwater speaker system in the world — is the brainchild of University of Minnesota scientists and has been up and running for about a week, officials announced Monday.

“It produces a sound that we know, from experiments in the lab and observations in the field, they hate,” said Peter Sorensen, a professor and lead researcher at the U’s Aquatic Invasive Species Research Center. “This is why they jump,” Sorensen added, referring to famous leaping proclivity of the silver carp, which has gained YouTube fame from videos showing the mayhem — and hazards — created by hundreds of fish, many heavier than 20 pounds, flinging themselves airborne as motorboats speed through their haunts.

More than mere hazards to recreational boaters, the carp are seen as a major threat to fish and other aquatic life throughout the Upper Midwest. The fish voraciously feed on plankton, the base of the food chain. In areas farther south where they’ve established themselves, Asian carp make up the majority of the biomass, to the detriment of native fish, mollusks and other life forms.

The possibility that invasive carp might someday crowd out cherished walleye, northern pike and bass in the headwaters of the Mississippi in the heart of Minnesota — and the economic impact that might have on the state’s freshwater fishing industry — has garnered attention from the highest levels of government, including summits convened by Gov. Mark Dayton and legislation proposed by the state’s congressional delegation. Earlier this year, Congress approved closing the Upper St. Anthony Falls lock in Minneapolis to convert the commercial navigation infrastructure into a carp barrier.

The sound system at Lock and Dam No. 8 is part of a larger strategy to slow the advance of the fish as much as possible; neither system is believed to be completely effective.

“We’re trying to buy as much time as we can while we learn more about these fish and how to deal with them,” Sorensen said Monday as the gates opened for a single motorboat passing through the lock.

“It’s the Achilles’ heel of the system,” said Sorensen, referring to how the opening and closing of lock gates can allow the carp easy access to any part of the river where locks operate.

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