Grass Carp Overstaying Their Welcome in Indiana

Fish introduced into the Great Lakes to help manage weeds could be overstaying their welcome. Grass carp feed on aquatic plants and new research finds they have been captured in places where they were not originally intended to be used. Post-doctoral researcher at the University of Notre Dame Marion Wittmann is lead author of the study.

“Grass carp, if they establish – and it’s not clear whether they’ve established yet – could come in and impact those wetland areas or some of the native plants, which in turn would have effect on other species,” Wittmann said.

Wittmann says the Great Lakes states have a wide variety of regulations about grass carp. They are strictly prohibited in Michigan and Minnesota, and in Wisconsin they are only allowed for research purposes. In contrast, Indiana, Illinois and Ohio allow the use of grass carp, but only those that have first been sterilized.

“They don’t reproduce, but we’d still get the benefit of using them as a weed control. So, all these different states have different permissions or different kinds of policies or regulations that make it hard to manage across the Great Lakes watershed,” said Wittmann.

Wittmann adds that the fish do have some beneficial qualities and she doesn’t think they should be banned entirely.

“Grass carp are a non-chemical alternative for treating aquatic weeds. So, by using grass carp what that means is that we don’t have to put pesticides in to remove weeds,” said Wittmann.

Wittmann believes the Great Lakes states should work to better coordinate their efforts and develop policies that can allow for the safe use of grass carp. Research indicates 45 grass carp are known to have been caught in the Great Lakes basin between 2007 and 2012, which is enough to be of some concern. The paper was published online by the Canadian Journal of Fisheries and Aquatic Sciences.