Invasive Carp Found Near St. Croix River

Carp that showed up in fishermen’s nets near St. Paul last week are an ominous omen for boaters and anglers on the St. Croix River.

Two types of invasive carp were found in the Mississippi River above its confluence with the St. Croix. One of the fish was a silver carp – the kind that leap out of the water when disturbed by boats – which had not been previously found upstream of Winona.

The Minnesota Department of Natural Resources announced that contract fishermen netted the fish on July 17th. The carp were found near Cottage Grove, in the stretch of river between Hastings and St. Paul called Pool 2. The catch included a bighead carp weighing 40 pounds, and the silver carp, which tipped the scales at about 20 pounds.

The agency said water levels this summer have been ideal for carp. The fish like to migrate upstream during floods, and the conditions have also forced officials to keep locks on the Mississippi River open, possibly making it easier for the fish to find their way upriver. “Such conditions existed for many weeks this year,” Brad Parsons, DNR regional fisheries manager, said in a news release.

The DNR plans to step up monitoring efforts in the area in the weeks ahead to find out if more — and younger, smaller — carp are present.

Threat to boaters and fish

Bighead carp have been previously found in the St. Croix River near Prescott. No invasive carp had been previously confirmed so far upstream on the Mississippi. Silver carp had not been detected above Winona, MN. They are known to be established in the Mississippi River below Muscatine, Iowa.

The bad news was compounded by the fact that both fish were females bearing eggs. “That’s concerning,” Parsons said. “Invasive carp pose a threat to our native fisheries, water recreation and ecosystems.”

According to the DNR, silver and bighead carp can grow to 60 pounds, and harm fisheries by consuming large amounts of plankton that native fish also rely on.

The leaping silver carp is notorious for harming boats and boaters. In the Illinois River near Peoria, IL, a study two years ago found that 33 percent of boats have been damaged by carp and 47 of boaters have been hit by flying carp. Marina owners said the boating business has all but disappeared on the river as a result.

Recent carp controls mixed bag for St. Croix

Two moves in recent months have sought to combat the carp invasion. In June, President Obama signed a bill that will close the Mississippi River lock in Minneapolis, seeking to prevent the fish from getting any farther upstream.

Because that lock is upstream of the St. Croix’s confluence, its closure offers no protection for the river.

On the other hand, a project being spearheaded by the University of Minnesota’s Aquatic Invasive Species Center could prevent more fish from reaching the upper Mississippi – and the St. Croix.

Five underwater speakers are being installed at Lock and Dam 8 near the Iowa border. Researchers believe that blasting sound through the water will prevent fish from moving upstream.

“We think it might have the same effect on Asian carp as a dental drill does on people,” researcher Peter Sorensen told the Star Tribune.

Carp are especially sensitive to sound, with ears 100 times better than native fish, Sorensen said. Scientists think silver carp leap from the water because they are afraid of motorboat sounds.