Thousands of invasive carp swim the channel of Ramsey County's Rice Creek and its connected lakes, rooting along the bottom and setting off a cascade of damaging effects that harm native fish, birds and plants.
Now University of Minnesota ecologists, who have spent years studying the life cycle of this unwanted fish in the Rice Creek system, are using that research coupled with new technology including "an electric fence for fish" to remove thousands of carp each spring.
"We will not meet our water-quality goals for these lakes without managing carp," said Matt Kocian, lake and stream specialist for the the Rice Creek Watershed District, which is managing the carp removal program.
The goal is to remove the carp, which will improve water clarity, lower algae blooms and support native species.
"There is a huge biomass of carp in that system," explained University of Minnesota assistant research professor Przemek Bajer, who is part of the U's Minnesota Aquatic Invasive Species Research Center. "To restore that system you need to remove 80 percent of those carp."
Last year, was their first full season of operation on Rice Creek in New Brighton. Bolstered by those promising results, they're back again this year for the spring spawn.
"It went well. We captured two-thirds of the spawning run. That's a little over 10,000 carp," said Bajer, who started the company Carp Solutions to develop technology and handle the removal.
Last summer, they removed an additional 6,000 carp with baited traps. The Rice Creek watershed includes Long Lake in New Brighton and the Lino Lakes chain of lakes in Anoka County.
"I think we put a big dent in the population last year," Kocian said. He said the watershed has invested about $200,000 in the equipment and installation. A state Clean Water, Land and Legacy Grant helped to kick-start the program. It will take several years to see results, they said.
Scientists have spent decades trying to remove invasive carp from American lakes and streams, often relying on seine fishing, which involves dragging a net across the bottom of a lake usually below the ice in the winter when the carp school.