Study weighs effect of bighead, silver carp in Lake Erie
TRAVERSE CITY, Mich. — Asian carp could become the most common fish in Lake Erie if the ravenous invaders develop a breeding population there, while popular sport species including walleye and rainbow trout likely would decline, scientists said Monday.
A newly published study based on computer modeling projected that bighead and silver carp, which are Asian carp species, eventually could make up about one-third of the total fish weight in Erie, which has the most fish of the five Great Lakes, even though it's the smallest by volume.
“They would be quite abundant,” said Ed Rutherford, a fisheries biologist with the federal Great Lakes Environmental Research Laboratory in Ann Arbor and member of the study team, which included scientists from several American and Canadian universities and government offices.
The carp, which have overrun the Mississippi River and many of its tributaries since being imported to the southern United States from Asia in the 1970s to cleanse sewage treatment ponds, gorge on tiny plants and animals known as plankton that all fish eat at some point in life. They are migrating north toward the Great Lakes, where agencies have spent more than $300 million to keep them out.
A few have been found in Lake Erie over the years, and some samples of its waters have tested positive for Asian carp DNA. But there is no evidence that it has self-sustaining populations of silver or bighead carp.
Even so, the study's findings underscore the significance of the threat, said Marc Gaden, spokesman for the Great Lakes Fishery Commission, a U.S.-Canadian agency.
“It's very sobering,” Gaden said. “Lake Erie is one of the most productive inland fisheries in the world. It wouldn't be as valuable by any stretch of the imagination if one out of every three pounds of fish were Asian carp.”
The study used an ecosystem modeling program and consultation with experts to estimate how Asian carp, which can weigh dozens of pounds and eat up to 20 percent of their body weight daily, would affect Erie's food chains.
It found they would pose stiff competition for other plankton eaters, including gizzard shad and emerald shiners, two of the lake's most important prey fish. The emerald shiner population could drop by as much as 37 percent. Adult walleye, a prized sport species, could decline by 10 to 15 percent.
Gizzard shad, which presently compose an estimated 23 percent of Erie's fish by weight, could fall to about 13 percent.
Not all native fish would fare poorly, said Hongyan Zhang of the University of Michigan, the report's lead writer. Ironically, Asian carp could give adult yellow perch a slight boost by driving down numbers of white perch, which feed on yellow perch larvae. Smallmouth bass could be another winner because their primary food source is round goby, which Asian carp don't eat.
The study was published last week in the journal Transactions of the American Fisheries Society. The research team plans similar modeling of potential Asian carp effects on Lakes Michigan, Huron and Ontario.