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 past five years, agencies such as the US Fish and Wildlife Service and Minnesota Department of Natural Resources have employed a new seek-and-destroy strategy that uses turncoat Asian carp to lead them to the gang's hotspot hideouts, the AP reports. 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 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 from the ecosystem. Kayla Stampfle, invasive carp field lead for the Minnesota DNR, says 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 a traitor fish and set the nets around this fish," she says. The carp are voracious eaters—adult bigheads and silvers can consume up to 40% of their bodyweight in a day—and easily outcompete native species, wreaking havoc on aquatic ecosystems. There is no hard estimates of invasive carp populations in the US, but they are believed to number in the millions.
Fisheries experts have employed a host of defenses, including electric barriers, walls of bubbles, and herding the carp into nets using underwater speakers. But the fish still have made their way up the Mississippi as far as northern Wisconsin, and grass carp have been found in Lake Erie, Lake Michigan, and Lake Ontario, leaving fisheries managers racing to blunt the incursion. 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.
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The traitor fish strategy has drawn muted criticism from the fisheries industry because managers return tagged invasive carp to the wild where they can breed, says Marc Smith, policy director at the National Wildlife Federation's Great Lakes Regional Center. But wildlife agencies need every weapon they can get against the carp, he said. "In theory, it works," Smith says. "We think the rewards outweigh the risk. We have to throw everything we can at them. I wouldn't want to take anything off the table." (Officials in Illinois hope renaming Asian carp "copi" will help persuade people to eat more of them.)
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