Mich. (AP) - Plant-gorging grass carp probably could survive in all of the
Great Lakes, scientists said Monday, adding that if the fish get
established, they might significantly damage the environment.
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.
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.
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
fish, Wittmann said. Largemouth bass and bluegill 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 study also
found that grass carp could live in all five of the lakes based on the
region’s climate, although more work is needed to determine whether all the
lakes have sufficient food supplies.
A hurdle to keeping
the carp out of the Great Lakes is the patchwork quilt of policies and
regulations, Wittmann said. Unlike bighead and silver carp, they are not
illegal to possess under federal law. 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.
“We’d like to the
see the Great Lakes states harmonize their policies,” said Tammy Newcomb,
senior water policy adviser with the Michigan Department of Natural
The U.S. Fish and
Wildlife Service tests grass carp at producer facilities to make sure
they’ve been sterilized before they are shipped to customers, such as
reservoir managers or homeowner associations around private lakes. The
inspections are not mandatory under federal law.
But even in
Michigan, where the fish have been banned since the late 1970s, grass carp
turned up in an inland lake in 2012. They were very old and apparently
stocked many years ago, Newcomb said.
The study shows the
importance of being vigilant but doesn’t suggest a need for emergency
actions to ward off a grass carp invasion, Newcomb said.
“The house isn’t on
fire as much as I’d feel like if we were finding reproducing bighead and
silver carp in the Great Lakes,” Newcomb said.