Mo. biologists try to control Asian carp

COLUMBIA, Mo. -- The fish tank at the U.S. Geological Survey's Columbia Environmental Research Center looked like it held a swirling black cloud. A school of juvenile Asian carp was clustered together and rapidly rotating from the outside of the school to the inside.

"They hate to be alone," said Robin Calfee, a USGS biologist who studies the carp.

The carp were acting like this because they were frightened; people were standing over their tank. One of the fish had released a chemical signal known as an "alarm cue," and the others reacted accordingly. The group clustered together to protect itself from a potential predator.

USGS biologists want to take advantage of this behavior. In groundbreaking research, Columbia-based scientists are looking at ways to use the carp's alarm pheromones, attraction pheromones or commercial bait scents to control the movement of carp populations that have taken over many Midwest waterways. They believe this research might hold the key to preventing the invasive species from spreading farther.

"The idea would be to keep them away from something like the entrance to the Great Lakes," said Duane Chapman, a USGS research fish biologist. "Also, we have very few" accessible "backwaters in the Missouri River, so we could use it to keep fish out of backwaters where juveniles would grow."

The two species of Asian carp -- bighead and silver -- have thrived for decades in Missouri and surrounding states. The fish are indigenous to the fresh waters of eastern Asia and were first brought here in the 1970s to be stocked in aquaculture ponds and sewage treatment lagoons. People viewed the carp as a natural way to control plankton growth.

But the fish escaped and today can be found in most large flowing waterways in the Mississippi River basin. Overall, they have been reported in 18 states nationwide, and their high fecundity rate -- females produce hundreds of thousands of eggs each -- and the lack of natural predators have led to a population explosion.

Efforts to control the carp have not succeeded. Illinois, for instance, has instituted an aggressive fishing program, and in 2006, fishermen on the Illinois River caught 2.3 million pounds of carp, more than two-thirds of the total catch that year. In subsequent years, the catch has been much higher, but officials have seen little to no drop in overall numbers.

"It's an uncontrolled experiment," said Rob Maher of the Illinois Department of Natural Resources, "because we don't know how many fish would be out there if these guys hadn't started harvesting. It doesn't appear to have collapsed the population. The Asian carp are alive and doing very well."

The invasive carp appear to be driving out several native species such as the big mouth buffalo and gizzard shad, according to published research. Anecdotal evidence from fishermen indicates walleye and sauger are scarcer and smaller then they once were along the Illinois River.

Matters have become so urgent that five states are suing the city of Chicago in federal court to close a 78-mile network of natural and man-made channels known as the Chicago Area Waterway System in an effort to prevent the carp from entering Lake Michigan. Chapman testified recently at the hearing for more than three hours.

The carp have not yet established themselves in any of Missouri's large lakes, but Chapman said if they do, the effect could be devastating.

"My prediction is that if these fish get into Truman Reservoir or Lake of the Ozarks and are able to establish large populations, that would be very bad," Chapman said, "and probably would have drastic effects on the numbers of crappie and walleye."

In this environment, research now under way by Calfee and Ecology Branch Chief Ed Little at the USGS CERC laboratories at 4200 E. New Haven Road could have a major impact. The researchers have evaluated the effectiveness of using alarm pheromones or "schreckstoff" to control Asian carp. In experiments, Calfee has taken a live carp and made incisions with a scalpel to simulate the attack of a predator. She then lets the fish sit in a tub of water for a short time and then extracts the water to release it into the tank. She said the response is almost immediate: The carp will exhibit heightened swimming in a school formation and attempt to quickly escape.

"Once a fish is attacked, the cells in the epidermis are broken and release these alarm cues," Calfee said. "They kind of send out a signal to the rest of the school that, 'Oh, there's a predator here; we better swim away."'

Calfee and Little also are working with sex pheromones and with commercially available baits in flavors such as fruit, Irish cream and squid and liver to determine what works best to attract carp.

Little said the team will collaborate with Peter Sorensen of the University of Minnesota, who has already identified and documented 260 chemical substances in the pheromones of the common carp. The researchers will monitor which pheromones produce the greatest response.

"Hopefully, we'll come up with a magic cocktail," Little said.