On Mississippi, invasive carp getting an earful from experimental underwater speakers
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.
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. Built during the Great Depression, the lock-and-dam system creates what is often called a gradual “staircase” for boats to ascend and descend the hundreds of feet of elevation difference between the Gulf of Mexico and Minneapolis, the farthest point upstream where commercial barges ply the river with goods ranging from coal to corn.
“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.
Individual fish have been found as far north as the Ford Dam (Lock and Dam No. 1) in Minneapolis-St. Paul, but no breeding populations are believed to exist above Lock and Dam No. 19 in Keokuk, Iowa, along the Illinois border. Many scientists believe the fish could thrive upstream but simply haven’t invaded in large enough numbers to support a breeding population.
Over the winter, scientists announced — mistakenly, it turned out — that they had discovered fertilized invasive carp eggs in the waters immediately below Lock and Dam No. 8 along the Minnesota-Wisconsin border. While they have since concluded the eggs were not fertilized eggs from invasive carp, the apparent discovery added urgency to Sorensen’s plan to adapt locks and dams to reduce the likelihood that carp could swim through them.
He and his team, including postdoctoral associate Dan Zielinski, designed a three-year plan to put their knowledge of carp into effect in Lock and Dam No. 8 in Genoa, Wis., which is below the Mississippi’s confluence of many important tributaries, including the Minnesota and St. Croix rivers.
The $75,000 sound system, paid for with state lottery funds and nearly $7,000 in private donations, is part of that plan. The other part involves adjusting the speed of waters flowing through the dam’s gates. Despite their leaping habits, it turns out the carp aren’t particularly strong swimmers, and the vast majority of them could be kept from swimming through the dam gates by changes to how the U.S. Army Corps of Engineers operates the dam, Zielinski said.
Such talk worries Mark Clements, who operates Clements Fishing Barge 300 feet downstream from the dam. The business, started by his grandfather in 1936, operates an array of fishing piers that cater to paying customers who want to catch any of the scores of fish species that inhabit the river, from catfish to walleye.
“The main concern for us is how is this going to affect the native fish,” Clements said Monday shortly before hailing Sorensen to discuss the project with him. Among Clements’ questions: Will the underwater speakers frighten off native fish that benefit from being able to migrate through the locks? And will changes to the flow of water coming through the dam gates alter the locations of game fish his business and its clients rely on?
To both questions, Sorensen and Zielinski say no.
Zielinski said the changes to the flow rates coming through the dam gates, which are routinely raised and lowered for flood control and commercial shipping needs, would be “subtle” and within the ranges the Army Corps of Engineers already sets.
As for the racket from the underwater speakers, Sorensen said invasive carp have hearing thousands of times more sensitive than native fish species, which shouldn’t hear the sounds as well. Nonetheless, he hopes to team up with federal and state researchers to monitor how native fish behave.
Under normal operation, the racket from the underwater speakers is hard to hear above the water. And unlike the blare beneath the surface, the sound is similar to crickets chirping.
At one point during Monday’s demonstration to the media, Zielinski cranked up the volume to broadcast a more recognizable — and ominous — sound. It was composer John Williams’ “Imperial March” from the movie “Star Wars.”
The Pioneer Press is a media partner with Forum News Service.