The recent capture of more than 300 invasive carp in the Mississippi River near Trempealeau, Wis. — by far, the biggest single catch so far upstream — has renewed calls for stronger efforts to stop the problematic fish.
Researchers from the Minnesota and Wisconsin natural resources departments have been tracking invasive carp that had been previously caught and tagged, hoping the “traitor fish” would lead them to hiding spots.
When they located six tagged carp in Pool 6 of the Mississippi, they sent a commercial crew which captured 323 invasive carp using seine nets on Nov. 30.
That included 296 silver carp — known for jumping out of the water and striking boaters — as well as 23 grass carp and four bighead carp.
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“It’s the largest capture we’ve ever had in Minnesota waters,” said Grace Loppnow, the DNR’s invasive fish coordinator. The agency has been keeping an eye on the location all year, since about 30 were caught near there last spring, she said.
Loppnow said the invasive carp likely swam upstream after flooding last spring, when dams are opened, allowing fish to pass through.
“We've been seeing more sightings and more captures, and also more detections of fish that were tagged downstream and moved up into Minnesota, following that flooding,” she said.
There's still no evidence that invasive carp are reproducing in Minnesota, such as eggs or larvae, Loppnow said. The age of the fish caught matches with known spawning events that occurred downstream, she said.
Still, some environmental advocates say the DNR should move quicker to stop invasive carp from establishing a permanent presence in Minnesota.
Invasive carp have been moving up the Mississippi River and other waterways since they were accidentally released into Arkansas waters in the 1970s. They are fast-growing and voracious eaters, outcompeting native fish for food and leading to a decline in biodiversity and water quality in rivers where they’re established.
Colleen O'Connor Toberman, land use and planning program director for the nonprofit Friends of the Mississippi River, called the recent catch “distressing.”
“I'm glad that 323 fewer carp are here in Minnesota, but that is far more fish than we've ever counted before,” she said. “And we don't know how many are here. We have no accurate sense of that.”
Friends of the Mississippi is a member of the Stop Carp Coalition, a group of environmental advocates that have called for installing a bio-acoustic fish fence at Lock and Dam 5 near Winona. It would use bubbles, lights and sound to deter carp from moving upstream.
Last session, the Legislature approved $1.72 million for the DNR to address invasive carp, far short of the nearly $17 million the Stop Carp Coalition had sought.
O’Connor Toberman said invasive carp may not be reproducing yet in Minnesota, but no one knows when that could occur, and a higher population would seem to make it more likely.
“Female silver carp can lay a million eggs a year per fish,” she said. “So once you have a mass spawning event, you may have completely lost control. And we just don’t know how close we are to that moment.”
The DNR is close to completing an invasive carp action plan on how to prevent the problematic fish from invading Minnesota waters. It should be done later this month, Loppnow said. The agency has started to spend the money appropriated by the Legislature last session, she said, including launching a study of changes in dam spillway gates that could help prevent invasive carp from getting through.
Loppnow said the DNR recently completed a strategic decision-making process with help from the U.S. Geological Survey to explore all options for managing invasive carp.
That includes acoustic deterrents, she said, but she added that they are not an immediate solution. They take time to design and install, and don’t prevent invasive carp already here from reproducing, she said.
“Being out there catching these carp, that’s the most immediate thing we can do,” Loppnow said.