Since escaping from ponds in Arkansas and making their way into the Mississippi River during floods in the early 1980s, the Asian carp, better known as the silver carp, has forced scientists to study ways to keep the populations under control and discourage the invasive species from invading other waterways in the Upper Mississippi River Basin.

And while tests performed by scientists at the U.S. Army Engineer Research and Development Center indicate methods like hydraulic flow and electrical containment show the potential for containing silver carp in areas where they haven’t already established themselves, there is another important issue to be answered — what to do with areas where the carp have become established.

“It’s one thing to keep them out, but it’s another thing to get rid of them, and that’s a fairly contentious issue, ERDC research fishery biologist Dr. Jan Jefferey Hoover said.

One suggestion is harvesting the carp as a food source.

“It would take (harvesting) 50 to 70 percent of the (carp) population to even get numbers down,” Hoover said, “and that model’s based on assumption that the fish do not reach a certain size, and do not reach a certain age. “What we’re finding is they’re living longer than we thought and they’re reaching sizes we never thought. The reason that size is a factor, is the number of eggs a female lays is disproportionate to her size, so if fish are getting a little bit bigger, they’re laying a lot more eggs, and there’s a lot more work to be done. The models for harvest need to be re-addressed.”

Another problem is the price commercial fishermen are paid for carp, ERDC research fisheries biologist Dr. Jack Killgore said.

“That’s the problem now, why should a commercial fisherman go after something that’s 10 cents a pound when he can catch buffalo (suckers) for 30 cents a pound?” he said.

The carp, however, are being actively caught.

“The Chinese have brought their own fishing crews over, and they’re out there constantly catching big head and Asian silver carp and fileting them and flash-freezing them and shipping them over to China,” Killgore said. “There are discussions of new plant in Kentucky (by an American company), a riverine fisheries that catches and processes the carp. They brought in a factory boat from Alaska. There’s more of a market for them in China.”

“There’s kind of a stigma about eating carp in the United States,” Hoover said. “There was a research effort on preparing and marketing carp. Calling the fish silver fin, because silver fin sounds better than silver carp.”

An indicator of how important the fish is outside the U.S., he said, came during a tour of the river by Chinese visitors that included displays of freshly caught American aquatic life.

“What they got excited about was when we brought out the Asian carp,” he said. “Their stocks are overfished. They have the opposite problem we have. We have too many Asian carp; they don’t have enough.”

And while the carp are having an adverse effect on native game fish in the area, the potential effect on Eagle Lake is unknown.

“If they get into Eagle Lake, then it’s kind of a waiting game,” Hoover said. “They’re not going to reproduce in the lake. We have some evidence that they may have reproduced in one Mississippi lake, but they just don’t normally reproduce (in lakes). They may release the eggs, but they don’t have spawning habitat, so you could see the numbers decline over time. Their eggs sink and they’re sticky, and they need to stick to gravel and packed sand; they have to have flowing water.”

Also, Killgore said, flowing water keeps the eggs suspended, too, where they don’t sink into the sediment where they’ll smother. It’s also possible that some carp leave the lake when the Muddy Bayou chute is open and head for flowing water to breed.

And why do they jump? There are several theories, the most popular of which is they are affected by outboard motors.

But Hoover said he has seen the same behavior when a net is drug through the water.

“It’s not the same noise as a motor, but you get a pressure wake like you do with a boat and you get a vibration as the net is moving through the water, so there’s some kind of vibratory or auditory stimulus that makes them do that.”

Hoover said a University of Mississippi graduate student working with ERDC believes the jumping is a way to escape predators, “because in the Yangtze (River), there are some very large fish and alligators that can eat them, so they may have evolved that behavior as a kind of evasion. The bighead carp typically are bigger, so they can escape predators buy simply being a bit larger.”

Hoover said scientists think the very large silver carp also don’t jump.

“We’re beginning to keep track of how big fish are when they land in a boat, and it seems when they get to a certain size like 700 millimeter size (about 2.2 feet), we’re not seeing them land in the boat any more. Once they reach a certain size, they’re not so aerodynamic, but they’re also of a certain size that something’s less likely to eat them.

“Small size school; larger fish jump; and extra large fish are safe,” he said.