Grass carp swimming Great Lakes could cause harm

Chicago — Plant-gorging grass carp probably could survive in Lake Michigan and each of the other Great Lakes, scientists noted in March, adding that if the fish get established, they might significantly damage the environment.

What’s that mean for Michigan anglers?

Largemouth bass and bluegills are among species that have fared poorly in places infested with grass carp. Ducks and other waterfowl that nest in wetlands also could be vulnerable.

The fight to prevent Asian carp from reaching the inland seas focused primarily on bighead and silver carp, which eat huge amounts of plankton, the foundation of aquatic food chains. They have infested much of the Mississippi River basin and are threatening to reach the Great Lakes through rivers and canals.

Grass carp have drawn less attention because they feed on plants, including nuisance weeds that choke boat motors and overwhelm native vegetation. Introduced in the United States in 1963 for pond and lake maintenance, the fish were distributed widely with the blessing of state and federal agencies; they’ve now been reported in 45 states.

Researchers documented for the first time last year that grass carp had spawned successfully in the Great Lakes, based on an analysis of four fish captured in Ohio’s Sandusky River, a tributary of Lake Erie.

In a paper published online by the Canadian Journal of Fisheries and Aquatic Sciences, researchers said 45 grass carp are known to have been caught in the Great Lakes basin between 2007-12. About half of those caught could reproduce, which could mean the lakes already have a breeding population, the report said, although there are other possible explanations, such as illegal stocking.

The researchers also surveyed scientific reports as far back as the 1930s showing that where grass carp have been introduced, they’ve mowed down a wide variety of plants and even algae.

“They’ll eat pretty much anything,” said lead author Marion Wittmann, of the University of Notre Dame. “I think of them as like sheep or goats; they’ll come in and munch what’s in front of them.”

That bodes ill for wetland vegetation that provides spawning grounds and habitat for young sport fish, Wittmann said.

The study also found that grass carp could live in all five of the lakes based on the region’s climate.

The fish is banned in Michigan and Minnesota; in Wisconsin, they can be used only for research. But the five other Great Lakes states – Illinois, Indiana, Ohio, Pennsylvania, and New York – allow their use with special permits.

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