Do snitches net fishes? Scientists turn invasive carp into traitors to slow Great Lakes push

Wildlife officials across the Great Lakes are looking for spies to take on an almost impossible mission: stop the spread of invasive carp.

Over the last five years, agencies have employed a new seek-and-destroy strategy that uses turncoat carp to lead them to the fish's hotspot hideouts.

Agency workers turn carp into double agents by capturing them, implanting transmitters and tossing them back. Floating receivers send real-time notifications when a tagged carp swims past. 

Carp are large fish with an even larger appetite. They tend to out-compete native species and destroy the ecosystems they take over. And that would have huge consequences for the Great Lakes. 

They often clump in schools in the spring and fall. Armed with the traitor carp's location, agency workers and commercial anglers can head to that spot, drop their nets and remove multiple fish.

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

"We use these fish as traitor fish and set the nets around this fish," she said.

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

LISTEN | Scientists turn carp into traitors in war to stop invasive species:

The big issue, according to Aaron Fisk, is where the Mississippi River meets Lake Michigan, near Chicago — about 15 to 20 kilometres away from entering the Great Lakes system.

"I think the impact is more going to be in places like the Thames River and the Sandusky Bay and places like that," said Fisk, who's a researcher with the Great Lakes Institute of Environmental Research (GLIER) at the University of Windsor.

"The concern is that they're going to eat a lot of the food at the base of the food web, potentially eat eggs of other fish and out compete some of the important lower level fish. Whether the impact is going to be huge is a big question."

Beginning around 2018, managers started placing new, solar-powered receivers around the Great Lakes region that could track tagged carp and send instant notifications to observers. 

The real-time notifications reveal where carp may be massing before a migration and illuminate movement patterns, allowing the agencies to plan round-up expeditions to remove carp from the environment and tag more traitor fish.

"We understand when they move and where they go and what time of the year and what are the environmental drivers of that happening. The sooner we can find them, if they actually get into the Great Lakes, the greater the chance we have of actually stopping them or minimizing their impact in the Great Lakes," said Fisk.

In a given year, binational efforts have seen close to 15,000 receivers put in across the Great Lakes, according to Fisk.

"You can't go more than about 10 kilometres in Lake Erie without seeing one at the bottom. They're just little black cylinders."

Calling it a "massive effort," he says they've tagged over 70 species of fish in the Great Lakes with a total of as many as 35,000 tags.

Stampfle and fish technician James Stone spent three hours in the Mississippi and Black rivers backwaters around La Crosse on a recent November day removing the receivers for the winter. She said the work is worth it.

"When are these fish moving? If we can figure that out, it gives us a fighting chance," Stampfle said as she guided her flat-bottom boat back to the landing. 

"Can we keep up with them? I don't think anyone can answer that accurately. It's still unknown territory. It's an uphill battle on a very slick slope. You just pray you have a foothold."