Operators of an electric barrier built on a Chicago canal to keep large flying Asian carp out of Lake Michigan have turned up the juice after genetic testing showed evidence of silver carp 5 miles from the barrier -- much closer than previously thought.

"These carp are clawing at the door now," said Marc Gaden, spokesman for the Great Lakes Fishery Commission, which deals with invasive species in the Great Lakes.

Voracious eaters, the carp feed on tiny plankton and can grow to 100 pounds. They reproduce in huge numbers. There are numerous videos of silver carp, which tend to be agitated by boats' motors, leaping out of the water, occasionally injuring boaters or anglers.

"These carp have the potential to be every bit as devastating as the worst invasives we have seen -- sea lamprey and zebra mussels," Gaden said. "That's what we're worried about."

Experts racing to protect nature's food web, humans

The race is on between man and fish, and the health of the Great Lakes is at stake.

At the end of June, scientists and experts thought silver carp, an aggressive invasive fish, were still 15 miles from an electric barrier built to repel them in the Chicago Sanitary and Ship Canal. The fish hadn't moved much in a while, giving federal officials time to gear up the newest section of the $30-million barrier.

But on July 31, results from a new testing method that samples water for fish DNA showed that silver carp already had moved through a lock and were 10 miles farther up the canal than anyone knew. The tests don't tell where the carp are now, only where they have been.

The Army Corps of Engineers doubled the voltage on the barrier Wednesday, but there are no guarantees. "It's not a silver bullet, but it's the best tool we have," said Col. Vincent Quarles, commander of the Chicago District of the corps.

"Given the tenacity of these carp species, I'm a bit pessimistic," said Mark Coscarelli, manager of the Great Lakes Fishery Trust.

The DNA test has been available only since May, Quarles said. More testing is being done to make sure fish haven't already crossed the barrier, heading the last 32 miles toward Lake Michigan with no significant obstacles in their path.

Until last week, the barrier operated at one volt per inch in quick pulses. Now, it's running at two volts per inch, pulsing every 6.5 milliseconds, which studies show should stun all sizes of Asian carp. But at that rate, it poses safety hazards to recreational boaters, who could be electrocuted if they fall in, and to barges carrying volatile cargo, if sparks fly. Tests are to continue through next week to make sure the new voltage level is safe for humans, Quarles said.

For nearly a decade, anglers and fish biologists have been concerned about the steady march of invasive Asian carp toward Lake Michigan, where they could migrate into other Great Lakes, spelling disaster for commercial and recreational fishing.

"Because they're filter feeders, they could significantly alter the food web," Coscarelli said. "They outcompete other fish."

Silver carp are on a federal list of injurious wildlife because of their risk to humans and aquatic life. If startled, they leap many feet into the air. Some have injured anglers and people using personal watercraft.

Three species of invasive Asian carp -- silver, black and bighead -- were imported in the 1970s and escaped from Southern fish ponds during floods, according to the U.S. Fish and Wildlife Service. They migrated up the Mississippi River and into the Illinois River, overwhelming native fish. In some spots, Asian carp make up 95% of the fish in the Mississippi, Gaden said. The international commission protects U.S. and Canadian fisheries in the Great Lakes.

To prevent the fish from getting into Lake Michigan, the Army Corps built a temporary, experimental electric barrier in the Chicago canal. That barrier began operating in April 2002, but it was low-voltage and not built to last. Under pressure from various groups, Congress authorized $30 million for a more permanent, two-part barrier. The first stage has operated since April; the second stage won't be finished until 2011.

"We've run out of time," said Gaden. He said what's really needed is a true barrier, such as one closing the Chicago canal inland from Lake Michigan.

If carp get past the barrier, various agencies plan an emergency response that could include using powerful chemicals to try to kill them, according to minutes of an advisory group's June meeting.

Coscarelli said the focus should be on preventing such species from arriving in the first place, rather than trying to control their spread.

"Silver carp is another poster child in our fight against invasive species," he said.

For the full article, see Tina Lam, "Huge, invasive flying carp gain ground in fight for lakes; Aggressive fish sneak closer to Lake Michigan, despite barrier", Detroit Free Press, August 17, 2009.