A new study has confirmed the tendency of at least one species of invasive carp to breed in flood waters.

Research published in the Journal of Freshwater Ecology examined habitats created by flooding in the Upper Mississippi River. A total of 12,700 fish were captured, with larval silver carp representing nearly 98% of the population.

“The results of this study suggest that shallow habitats at the edge of the flood have been an underappreciated habitat for larval silver carp in the Upper Mississippi River system,” the researchers said.

In 2019, flooding on the Mississippi River and its tributaries throughout the Midwest caused $6.2 billion in damage. It was the second wettest year on record in the US, according to the National Oceanic and Atmospheric Administration.

And although 2020 is not expected to be as severe, there is growing concern that further flooding could lead to costly proliferation of the invasive species, with this latest study showing peak catch rates occurred near the confluence of the Illinois and Mississippi rivers

‘Worrying’ upstream movement

The research coincides with the discovery of 51 invasive carp in the Mississippi River, near La Crosse and Trempealeau. The catch by commercial fishermen is the largest yet seen in Wisconsin or Minnesota, heightening fears that the invasive species are spreading upstream.

Marc Schultz of the La Crosse County Conservation Alliance told the Milwaukee Journal Sentinel the haul of 40 silver carp and 11 grass carp is “very worrying”.

“Obviously we have a great concern about it,” he said. “Does this represent an invasion that will never be turned back? Or is it a bunch of fish that made it up here but won’t be able to spawn?”

No successful spawning of silver or grass carp has yet been documented in Wisconsin or Minnesota waters. However, the US Fish and Wildlife Service will carry out tests to determine if any of the recently discovered fish have spawned in the past.