Commercial fishermen caught the highest number of silver carp ever found so far upstream in the Mississippi River this week.
The catch shows that the invasive fish are on the cusp of becoming intractable in Minnesota and Wisconsin, and have been gathering below one of the last barriers left between them and the upper Mississippi, Minnesota and St. Croix rivers.
The fishing operation pulled up 30 silver carp on Monday downstream of Lock and Dam 5 near Winona, Minn. They were all about the same age — seven years old — and likely passed a series of locks and dams together during the 2019 floods to make it so far north, said Heidi Wolf, a section manager for the Minnesota Department of Natural Resources.
The DNR hires commercial operations each spring and fall to target invasive carp.
"The hope is if we get enough out and get rid of them we can keep them in low numbers," Wolf said.
The agency will lead a larger operation in the same area in April — a coordinated effort to use noise, electricity and large nets to herd carp into smaller and smaller areas until they are able to be pulled out in a single seine net.
Silver carp, which grow to be 40 pounds, threaten both the ecology of the state's rivers and the people who use them. As they have advanced up the Mississippi River since the 1970s, they have become notorious for jumping from the water en masse when boats drive by, breaking people's noses and jaws. They've also cleared out up to 90% of large zooplankton in the water, an important food source for young fish. Numbers and sizes of popular game fish, such as bass and crappie, have fallen in the parts of the Mississippi where silver carp have taken over.
Individual carp have been caught as far north as the Twin Cities in the Mississippi, and have been found in the St. Croix and Minnesota rivers in recent years as well. There is still no evidence that the fish are reproducing inside the state. But if enough of them were able to make it past Lock and Dam 5 it will only be a matter of time, said Peter Sorensen, a University of Minnesota professor who has been researching carp deterrents and barriers for years.
"Once this is lost, it's lost forever," Sorensen said. "That amount of fish is very disturbing. It's hard proof that there's a substantial number of them here."
Sorensen, along with other university researchers and several environmental nonprofits, have asked lawmakers to build a $17 million barrier at Lock and Dam 5. It would use bubbles, noise and lights to keep carp from following barges and other boats through the lock. The proposal, which was heard in a Senate committee Thursday, would also give the DNR more funding to keep up fishing operations each spring and fall to thin the numbers of carp gathering below the dam.
Legislators will decide in the coming weeks whether to include the funding in the state's environmental budget.
The barrier and fishing operations working together won't be perfect, but it will buy time and could keep carp from spreading north for several decades, Sorensen said.
Wolf wouldn't say if DNR leaders support the plan. She said the DNR is working with other agencies to evaluate potential barriers and deterrents and expects to make recommendations by the end of the year.
But the catch shows that there is little time left, said Colleen O'Conner Toberman, land use director for Friends of the Mississippi River.
"No state or federal agency has presented a plan," she said. "This is the only option we have."
Sorensen has helped the U.S. Fish and Wildlife Service set up similar barriers in Kentucky and Tennessee, in rivers that were already overrun by the fish.
"If we miss our chance to stop at Lock and Dam 5, we will need to spend millions in each budget for fish removal," said state Sen. John Hoffman, DFL-Champlin, who introduced the proposal.
