TRAVERSE CITY — Plant-gorging grass carp probably could survive in all of the Great Lakes, and if they become established, the fish that’s native to Asia might significantly damage the environment, scientists said Monday.
The fight to prevent Asian carp from reaching the inland seas has 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, leading the government to spend more than $200 million on measures to keep them out.
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 U.S. 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 this month 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. Some were found in Lake Erie, others in tributaries of the lakes.
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.”