Do snitches fish with nets? Scientists turn invasive carp into traitors to slow their advance toward the Great Lakes

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LA CROSSE, Wis. (AP) — Great Lakes wildlife officials are looking for spies to accomplish a nearly impossible mission: stopping the spread of invasive carp.

Over the past five years, agencies such as the U.S. Fish and Wildlife Service and the Minnesota Department of Natural Resources have employed a new search-and-destroy strategy that uses upturned carp to lead them to the fish’s hiding places.

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Agency employees turn the carp into double agents by capturing them, implanting transmitters and discarding them. Floating receivers send real-time notifications when a tagged carp swims past. Carp often gather in schools in spring and fall. Armed with the location of the treacherous carp, temp workers and commercial fishermen can head to that location, cast their nets, and remove several fish from the ecosystem.

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Kayla Stampfle, invasive carp field manager for the Minnesota DNR, said the goal is to monitor when the carp start moving in the spring and use the marked fish to ambush their brethren.

“We use these fish as treacherous fish and set the nets around that fish,” she said.

Four different species are considered invasive carp: bighead carp, black carp, grass carp, and silver carp. They were imported to the United States in the 1960s and 1970s to help rid southern fish farms of algae, weeds and parasites. But they escaped through flooding and accidental releases, found their way into the Mississippi River, and used it as a superhighway to spread north into the rivers and streams of the middle of the country.

Carp are voracious eaters – adult bigheads and silver fish can consume up to 40% of their body weight in a day – and easily outcompete native species, wreaking havoc on aquatic ecosystems. There are no precise estimates of invasive carp populations in the United States, but they are estimated to number in the millions.

State and federal agencies have spent a combined $607 million to stop the fish, according to Associated Press figures compiled in 2020. Spending is expected to reach $1.5 billion over the next decade.

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But wildlife and fisheries experts say it would be nearly impossible to eradicate invasive carp in the United States. Simply stopping them from entering the Great Lakes and protecting the region’s $7 billion fishing industry would be a success.

Fishing experts have used a range of defenses, including electric barriers, bubble walls and corralling carp into nets using underwater speakers. But the fish still moved up the Mississippi into northern Wisconsin and grass carp were found in Lakes Erie, Michigan and Ontario, forcing fisheries managers to rush to mitigate the incursion.

Agencies such as the U.S. Fish and Wildlife Service and state wildlife managers have built a network of receivers stretching from the St. Croix River in far northern Wisconsin to the Gulf of Mexico to record the movements of marked invasive carp, with periodic data collection. The first receivers were deployed in the Illinois River in an effort to stem migration to Lake Michigan in the early 2000s.

Starting around 2018, managers began installing new solar-powered receivers in the Great Lakes region that can track marked carp and send instant notifications to observers. Real-time notifications reveal where carp may be congregating before a migration and illuminate movement patterns, allowing agencies to plan round-up expeditions to remove carp from the environment and tag more treacherous fish.

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The receivers are essentially a raft supporting three solar panels and a locked box equipped with a modem and a computer that records contact with tagged carp. The receivers can pick up signals from tagged fish more than a mile away, Fritts said.

He estimated that each receiver costs about $10,000. The Federal Water Reform and Development Act of 2014 authorized a multi-agency offensive against invasive carp in the upper Mississippi and Ohio basins, allowing the USFWS to spend on these devices in the within its existing budget.

Agencies have deployed the devices in Lake Erie, a portion of the Mississippi between the Illinois and Missouri borders, the Illinois River and Chicago-area waterways, Fritts said.

The USFWS has installed four real-time receivers in the Mississippi backwaters, which extend from Davenport, Iowa, to the Missouri border. The U.S. Geologic Survey has installed more than a dozen devices, including receivers in the Chicago Sanitary and Ship Canal, the Des Plaines and Illinois Rivers in Illinois; and the Sandusky River in Ohio.

The Minnesota DNR began deploying live receivers in the Mississippi backwaters forming the Minnesota-Wisconsin border around La Crosse three years ago. The agency welcomed four grantees this year, funded largely by federal grants. Plans call for seven next year.

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Wildlife agencies continue to consolidate data on the number of invasive carp that real-time tracking has allowed them to eliminate, said Janet Lebson, a spokeswoman for U.S. Fish and Wildlife.

But they say the treacherous fish tactic is worth it, pointing to results in Mississippi, from the Illinois-Iowa Quad Cities to the Iowa-Missouri border. Real-time tracking has helped wildlife managers and anglers double the weight of invasive carp removed from that area of ​​the river each year, said Mark Fritts, a fish biologist and telemetry expert at the Bureau of USFWS LaCrosse.

The strategy has drawn moderate criticism from the fishing industry because managers return marked invasive carp to the wild where they can reproduce, said Marc Smith, policy director at the Great Lakes Regional Center of the National Wildlife Federation. But wildlife agencies need every weapon they can get against carp, he said.

“In theory, it works,” Smith said. “We believe the rewards outweigh the risks. We have to throw everything we can at them. I wouldn’t want to take anything off the table.

Stampfle and fishing technician James Stone spent three hours in the backwaters of the Mississippi and Black rivers around La Crosse on a recent November day to remove receivers for the winter. She said the work was worth it.

“When do these fish move?” If we can figure that out, it gives us a fighting chance,” Stampfle said as he guided his flat-bottomed boat toward the landing. “Can we follow them?” I don’t think anyone can answer this accurately. This is still uncharted territory. It’s an uphill battle on a very slippery slope. Just pray for a foothold.

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