An invasive carp was caught Monday in the St. Croix by a commercial fisherman near the confluence of the river and the Mississippi. The catch has big implications for the future of native fish, like walleye and bass.

Unfair competition

A press release from the Minnesota Department of Natural Resources says the bighead carp can out-compete other fish for food and replace them in lakes and rivers. In places like Missouri, the carp make up about 90 percent of the fish. The DNR website also says:

They eat huge amounts of plankton and detritus. Because they feed on plankton, these fish compete for food with native organisms including mussels, larval fishes, and some adult fish such as paddlefish. This competition for food could result in fewer and smaller sport fish.

The carp were first found in Minnesota in 1996, in the St. Croix. The next one was not found until 2003, in the Mississippi. Since then, four more have been found in the Mississippi. Besides the fish caught in 1996 in the St. Croix, the others have been caught far downstream on the Mississippi, in Lake Pepin or south.

Locking the gate

With this week’s catch reinforcing the idea of the fish continuing to slowly migrate upstream, state officials are discussing ways to prevent them from infesting the entire river system.

The St. Croix has a natural barrier at the dam in St. Croix Falls, with no lock to allow boats–and fish–through. The lock-and-dams on the Mississippi are a concern though, and the DNR said it is looking at how it can secure them, particularly the Coon Rapids Dam, to prevent the carp from spreading to the upper reaches of that river.

The Pioneer Press reports:

Now, the DNR wants to establish a barrier by upgrading the Coon Rapids Dam or by closing the St. Anthony Falls locks, according to Luke Skinner, who heads the DNR’s invasive species program.

Gov. Mark Dayton has included $16 million for the Coon Rapids Dam in a public works bonding proposal, but Republicans controlling the Legislature don’t want to pass such a bill until next year.

The U.S. Army Corps of Engineers, meanwhile, manages the St. Anthony locks and dams for commercial navigation.

“We don’t have the discretion to just shut the locks and dams for stopping invasive species,” said Elliott Stefanik, a biologist for the corps’ St. Paul district. “Any closure would have to come from Congress.”

The “best’” solution might have come from a commenter on the St. Croix Facebook page. The sarcastic Aaron Bertini said:

The algae came from phosphorus we use to make our grass green, the carp were introduced to eat the algae. I just came up with a great idea!! Let’s introduce some African crocodiles to our rivers, they will eat all the carp!! Or maybe some great white sharks??