Changes to lock and dam aimed at stopping invasive carp

The U.S. Army Corps of Engineers has adjusted the flow of water through a Mississippi River lock and dam in southeastern Minnesota in an effort to slow the spread of invasive carp, which have been discovered as far north as Redwood Falls in the Minnesota River.

The changes to Lock and Dam 8 near Genoa, Wisconsin, were based on recommendations from a research team led by Peter Sorensen, a University of Minnesota professor and expert on invasive carp.

Sorensen said it's the first time the Corps of Engineers has adjusted a dam's operations to prevent the spread of an invasive species.

"If we could stop them there, there would be only a very short stretch of Minnesota they'd ever get into," he said.

Sorensen's research team found that the water flows through the lock and dam weren't always even.

"We figured out that they were unbalanced, and then how to correct the balance," he said. "In the course of doing that, you take away any weak spots that the fish might be able to swim through."

The relatively small adjustments in how the spillway gates are operated will prevent carp from moving upstream without affecting barge traffic, Sorensen said. He believes the low-cost, relatively simple changes could be replicated at other sites along the Mississippi and elsewhere.

"It's going to be much cheaper and easier if you do it proactively before they've passed through a spot and are actively breeding and moving around," Sorenson said.

Researchers also have mounted underwater speakers in the lock gates to broadcast low-frequency noises that deter carp, but aren't known to affect native species in the river and are not audible to people.

Bighead, silver and other invasive carp have been making their way upstream since escaping into the Mississippi River in the 1970s. These large fish are voracious eaters that compete with native species and pose a threat to rivers and lakes.

While no breeding populations have been detected in Minnesota waters, individual fish have been caught in the Mississippi near the Twin Cities, the St. Croix River and the Minnesota River.

The largest invasive carp ever found in the state was caught by an angler June 4 in the Minnesota River watershed upstream from Mankato.

The 61.7-pound bighead carp was nabbed by a bow angler in a private gravel pit near Redwood Falls and is believed to have reached the pond during recent flooding of the nearby Minnesota River. The fish was more than twice as big as the first bighead carp to be caught in the river, a 25-pounder netted by commercial fishermen seining for rough fish near New Ulm in February 2016. The carp caught in June was 80 miles farther upstream than the New Ulm fish.

According to the Minnesota Department of Natural Resources, bighead and silver carp are now abundant and reproducing in Iowa, about 100 miles south of Genoa, and are moving north.