Minnesota fishery managers and commercial boats will spend much more time on the water this year hunting down and fishing out invasive carp whose populations seem set to explode in the Mississippi River.
The Minnesota Department of Natural Resources updated its carp plan Thursday for the first time in a decade. The strategy is more aggressive in the way the state will track, monitor and remove the silver, bighead and grass carp already in Minnesota waters.
But the plan calls for more study before installing permanent light, sound and bubble barriers at two lock and dam structures in the river, a measure proposed by university scientists and river advocates. Lawmakers considered the proposal last year, but they decided against funding it as they waited for the DNR to update its overall carp strategy.
Studies led by Peter Sorensen, a professor and carp expert at the University of Minnesota, show the deterrents would be particularly effective at Lock and Dam 4 and Lock and Dam 5, which are about 10 miles north of Winona. The barriers would deter carp from following barges and other watercraft through the lock. Lawmakers gave the DNR $1.7 million last year, with part of the money meant to study the deterrent.
Heidi Wolf, a DNR section manager, said the agency has talked with the Army Corps of Engineers, the owner of the structures, about what it would take to install the deterrents.
"It would need several levels of environmental review," she said.
Under the plan, the DNR said it will continue to study the deterrent over the next four years.
That's not quick enough, said Colleen O'Connor Toberman, land use and planning director for the advocacy group Friends of the Mississippi River.
"We need to get this in place as quickly as possible," she said. "We don't know how close we are to a tipping point. No one can tell us how much time we have left before they start reproducing here."
Invasive carp have been working their way north in the Mississippi River since the 1970s, when fish farms and sewage treatment managers in the American South imported them from Asia to clean algae.
Some of the carp can grow to more than 100 pounds. They upend native ecosystems by eating up to 20% of their body weight daily. Silver carp, which grow to about 20 pounds, gather in schools and leap out of the water en masse when scared, sometimes injuring boaters and water skiers.
The fish have already overtaken large portions of the Mississippi and its tributaries in Iowa, Illinois and Kentucky, where state and federal taxpayers have spent tens of millions of dollars trying to remove them.
While the DNR said there is still no evidence that the carp are reproducing in Minnesota, sightings and capture of the fish have been increasing exponentially every year since 2018. Fewer than 10 of the fish were caught in Minnesota then. More than 450 were caught in 2023, including a record catch of 323 at once in November near Winona.
Those fish were caught with a strategy that the DNR hopes to continue in coming years. The agency put tracking devices on a handful of the carp and released them back into the river. The fish have guided DNR workers and commercial fishing operators to schools and gathering spots ever since.
The DNR's plan would strengthen the agency's tracking program and partnership with commercial fishing operations.
"Commercial fishing is currently the most effective way to capture invasive carp," the plan says.
The DNR said it wants to spend 100 days a year on the water fishing out carp and sending commercial fishing captains, with their seine nets and years of experience, to the small pockets of the river where the tagged fish lead them. For comparison, the agency actively fished for carp a total of 38 days in 2023.
The state would also install 30 more tracking receivers to cover gaps in the river where tagged fish currently go dark on monitors, and put tracking devices on more individuals.
Sorensen praised the actions as strong, but called for more urgency.
"I'm glad to see they're taking this seriously, but four years is a long time," he said. "We need this deterrent. There's only one Mississippi River and once it's broken, there is no fix."
The state's plan supports a permanent light, sound and bubble system at Lock and Dam 19 in Keokuk, Iowa. The deterrent system was temporarily installed there a few years ago, while another was added to the Barkley Lock and Dam on the Cumberland River in Kentucky. Carp have already infested those areas, reproducing on both sides of the dams.
According to the DNR, early data shows that the systems cut invasive carp passage in half while having no effect on native species, which are less skittish about noise.
The deterrent system could cost between $10 million and $15 million to install in Minnesota. The DNR's plan doesn't specify how much it will cost to enhance the state's tracking and fishing efforts. Many of its current programs have been paid with federal grants or one-time appropriations from lawmakers. The agency said it will need a reliable source of funding.
