Field Notes - Big Carp Problem

Mark Pegg never imagined he would be dodging 15-pound airborne carp when he became a research biologist for the Illinois Natural History Survey.

Today Pegg, who has been doing fieldwork on the Illinois River near Peoria since 2000, ducks "flying" carp almost every time he's out. Like many boaters who frequent the Mississippi and its tributaries downstream from central Iowa, Pegg and his research crew are often hit by silver carp, which leap at the sound of boat motors. The silver is one of four ecosystem-disrupting Asian carp species introduced into the United States about 30 years ago by fish farmers in southern states to control vegetation and algae blooms. Black carp have not been documented in the wild. But grass, bighead, and silver carp have been released or have escaped to the wild and are reproducing in streams of the Mississippi River basin.

Bighead and silver carp are making their way up the Illinois River toward Lake Michigan, the Missouri River to South Dakota, and the Mississippi River toward Minnesota. Free-roaming grass carp have been reported throughout the Mississippi and are known to spawn downstream of the Iowa-Missouri border.

Bighead and silver carp feed voraciously on plankton and grow faster than native paddlefish, bigmouth buffalo, and sturgeon. Grass carp could destroy habitat for fish and waterfowl if they become established in wetlands.

Bighead carp can weigh up to 100 pounds; silver carp are slightly smaller. Both fish have large heads with eyes set close to the mouth, giving them the appearance of being upside down. Both grass and black carp have elongated bodies with dark scales and can weigh up to 50 pounds.

Bighead and silver establish and reproduce quickly. Pegg said an angler discovered the exotic carp in the 120-mile-long La Grange district of the Illinois in 1996. "Now we find them in just about every backwater, bay, and inlet in the entire basin."

While boaters suffer bumps and bruises from silver carp leaping, exotic carp pose a larger threat to native fish, according to survey research biologist John Chick.

Chick and Pegg are studying how bighead and silver carp will affect the food supply for gizzard shad, bigmouth buffalo, and paddlefish. Chick said anecdotal evidence and some results from their research point to the possibility of serious problems in the future.

"It's still too soon to see the trend toward less robust native populations," Chick said. "But we've heard reports, especially from commercial fishermen, of bigmouth buffalo in poor condition. That could be the first sign of problems related to bighead carp."

The invaders could have an impact on other fish species too. "Just about every fish species feeds on plankton at some point during its life cycle," Chick said. "In addition, fish species further up the food chain are affected when forage fish that depend on zooplankton and phytoplankton, like gizzard shad, are depleted."

Although one bighead carp was found in Lake Pepin in October, there's no evidence the fish are reproducing in Minnesota waters of the Mississippi, according to Jay Rendall, DNR Exotic Species Program coordinator.

A commercial fisherman netted the 23-pound bighead in Lake Pepin, 100 miles upstream of previous discoveries. Silver carp are thought to be still farther downstream.

Rendall is working with state and federal agency representatives to keep the fish out of Minnesota. Among the options the group is exploring are electric and acoustic barriers across the river.

Chick and Pegg have found electric and acoustic barriers slow the movement of carp, but they say no method is 100 percent effective. And, according to Chick, a barrier across the Mississippi would have to be 100 percent effective to stop the carp. In addition, the carp, which have been found in Siberia, are unlikely to be affected by Minnesota's cooler water temperatures. "We know that bighead and silver carp would easily find sufficient spawning areas in Minnesota," he said. "If just a few fish got beyond the barrier, they would be able to establish a population."

Other strategies being considered include developing pheromones to attract the carp to nets or repel them from locks and dams or other points along the river.

Chick said it's important for fisheries specialists to try to stop the fish. "It costs more to get rid of invasive species once they're established than it does to prevent them from getting established in the first place," he said.

Jason Abraham