Federal scientists say they've found evidence for the first time that Asian carp have reproduced successfully within the Great Lakes watershed.
U.S. Geological Survey experts report Monday that four grass carp taken from the Sandusky River in Ohio originated there, instead of being moved from elsewhere. The Sandusky is a tributary of Lake Erie.
Grass carp are among several invasive species imported to the U.S. from Asia decades ago.
Experts are more concerned about keeping bighead and silver carp out of the Great Lakes because they eat plankton that is crucial for other fish. But scientist Duane Chapman says bighead and silver carp have similar spawning requirements to grass carp.
He says the discovery indicates that controlling Asian carp will be difficult if they become established in the Great Lakes.