Dozens of sturgeon, northern pike, catfish and even gar were caught in the shallow backwaters of the Mississippi River by a formidable fishing operation this week. But the one fish that state and federal agencies could not pull up in their nets was the one they were after — the dreaded silver carp.
It's a good sign in one sense — that the invasive carp, which upend ecosystems and injure boaters when they jump out of the water, still don't have high enough numbers in Minnesota to be easily caught. But it's disappointing, too, because biologists know the fish are here, and Minnesota is running out of time to come up with a way to stop them from spreading further.
"It's a mixed bag," said Grace Luppnow, invasive fish coordinator for the Minnesota Department of Natural Resources (DNR).
The DNR's goal is to tag and track some silver carp to learn more about where and how deep they go, how they survive and what water temperatures they prefer. It's a change in philosophy from the recent past, when the state sought to kill all silvers on sight.
The fish, native to Russia and Asia, have been slowly spreading north for decades, along with big head and grass carp, taking over much of the Mississippi River after being released by aquatic farmers in the South.
The lock and dam system in Iowa and Minnesota has slowed them, but the fish have continued to make it past the barriers whenever the water is high enough for them to swim through open gates.
Last year, Wisconsin and Minnesota started working with federal fisheries experts on a coordinated netting method to capture carp from the pools they frequent. About a dozen boats set nets at choke points, trapping all the fish in the area. They then herd them into smaller and smaller areas using electric pulses and noise makers. Eventually, the fish are corralled inside a single seine net and pulled up. All the native fish are safely released, while the invasive carp are either euthanized or tagged.
The agencies caught about 50 silver carp in 2021 using the method. Last week they pulled up none.
"We did see six silvers jump out of the water before we could catch them," said Kayla Stampfle, invasive carp field lead for the DNR.
The carp only seem to spawn when there are high numbers of the fish around. It could have something to do with the amount of pheromones in the water, Stampfle said.
So while carp are caught in Minnesota every year, there isn't any evidence they're abundant enough to reproduce.
The U.S. Fish and Wildlife Service out of La Crosse, Wis., has tagged and followed a small handful of invasive carp over the past two years. The fish each have their quirks, said Mark Fritts, conservation officer.
"We have some that are true homebodies, that stay right around where we tagged them," he said.
Others immediately swam back south to Iowa and haven't been seen in Minnesota since. One carp hung out for months right by the power plant where it was caught until it suddenly bolted north, swimming about 35 miles in one day. Nobody has determined what it was seeking.
Because carp school up together, the tagged fish have led to bigger captures. The hope is that the DNR will be able to tag enough of them to find out where they spend the winter, Stampfle said.
"We have a few spots in mind, but we just haven't gotten enough tagged silvers to figure out their wintering spots," she said.