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Environmental News

DNR puts silver carp back into the St. Croix, hoping to learn its ways

A person holds a fish in water
This is the silver carp that the Minnesota DNR captured and tagged in the St. Croix River. The agency released the invasive fish back into the river to study its movement.
Courtesy of Minnesota DNR

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State conservation officials say they’ve tagged and released a silver carp into the St. Croix River for the first time as a way to learn more about the invasive creature’s habits and movements.

On Tuesday, Minnesota Department of Natural Resources staff and a contracted commercial fishing crew were tracking and trying to net a tagged bighead carp. Instead, they caught a silver carp about 2 miles south of the Interstate 94 bridge over the St. Croix River.

The crew inserted a tracking device in the fish and released it back into the river to learn how far and often it’s moving and where it’s hanging out, said Nick Frohnauer, the DNR's invasive fish coordinator.

Silver carp are the kind that in other states are known to leap out of the water, causing havoc for boaters.

Minnesota, though, does not have a reproducing population of invasive carp, so there’s little risk with releasing the caught fish back into the river, Frohnauer said.

“Invasive carp need more than just two individuals to reproduce,” he said. “How many we don't know for sure, but it's more than two. It's probably over 10. So putting one back doesn't make a big difference.”

On the other hand, invasive carp tend to stick together, so Frohnauer said they hope the tagged fish will lead them to others.

“This is the sixth individual that we’ve caught because of following the tagged bighead carp,” he said. “So we hope for similar results with this fish, too.”

Invasive carp progressed upstream since escaping into the Lower Mississippi River in the 1970s. These large fish compete with native species and pose a threat to rivers and lakes.

Individual invasive carp have been caught as far upstream in Mississippi River Pool 2 near the Twin Cities.

This is the 12th invasive carp caught in Minnesota rivers this year, a slight uptick from previous years. That’s likely due to so-called open water conditions on rivers this spring, when lock and dam gates are lifted to let more water through, Frohnauer said.