Giant Carp May Eat Up Great Lakes

CHICAGO – It's been referred to by scientists as a marine vacuum cleaner and it has made its way into the waterways of the Midwest.

Now the race is on to keep this invasive fish out of the Great Lakes, where scientists worry it could throw off the balance of the ecosystem and threaten the lives of thousands of other fish.

Since the mid 1990s, populations of two types of Asian carp — silver and bighead — are estimated to have increased by more than a thousand along a stretch of the Illinois River. And they’re getting harder to control by the day.

The fish were imported from Asia for aquaculture purposes in the early 1970s and escaped from fish farms in the South in the early nineties, before making their way into the Mississippi River Basin, then up the Mississippi and Illinois Rivers.

Scientists say Asian carp produce millions of eggs a year and can eat up to half their weight every day. And so they grow fast — up to 12 inches and 12 pounds in one year. Some species of Asian carp have been known to tip the scales at more than 100 pounds, and eclipse lengths of about 6 feet.

The food of choice for the Asian carp is zooplankton, which are tiny animal organisms at the bottom of the food chain that are favored by many species of fish. The Asian carp has the ability to devour these organisms down to the size of 4 microns, which is about as small as bacteria.

The fish don’t even have a true stomach — food goes in one end and waste goes out the other as they devour their meals. Their appetite is so voracious that the carp end up "knocking the stool right from under the food chain," said Jerry Rasmussen of the U.S. Fish and Wildlife Service.

Scientists fear that if the fish continue upstream into Lake Michigan to cooler waters, they will consume all the food native fish such as largemouth bass depend upon, ultimately wiping them out because they don't have a food source. Some scientists say the waterways of the Great Lakes are already under great stress, because it is already chock full of other invasive species.

The invasion of the giant carp "could be the final straw to break the camel’s back," according to Mark Pegg, a scientist with the Illinois History Survey, which is a group that has been studying the Asian carp. "Once a fish gets through a barrier and into a new ecosystem, they tend to take off in large numbers because there’s no natural predators, no diseases," Rasmussen said.

The carp also pose a threat to humans.

They are capable of jumping up to 10 feet in the air and into fisherman’s boats. They also jump up at water-skiers and others in the water.

"They come right up and jump right in the boat, or jump over the boat," said Jerry Carlock, a commercial fisherman. "I’ve known guys that have gotten hit beside the head."

"We’ve had several staff members hit by these guys when we’re sampling," said Pegg. "We’ve had stories of people with broken noses, black eyes. So there’s a very high risk of getting hurt when you’re out here on the river these days."

At this point, scientists say there is no hope of eradicating them, so they’re trying to contain the population.

"They’ve established themselves," Pegg said. "There’s no hope of getting them out of the Illinois River … the impetus now is to keep them from getting into the Great Lakes."

One method is electric shock treatment.

Earlier this year, The U.S. Army Corp of Engineers installed a $2.2 million electrical barrier in the Chicago Sanitary and Ship Canal, which is the sole waterway linking the Mississippi River basin with the Great Lakes basin. A series of low-voltage electric cables have been placed underwater with the intent of shocking the fish as they try to swim toward the Great Lakes to force them to turn around.

"As far as we know, this is the largest electrical barrier in the world," said Beldon McPheron of the U.S. Army Corp of Engineers. "The fish come up to that. They feel uncomfortable. They turn around and go the other way."

But some worry this tactic won't work.

The carp have yet to reach the electrical barrier, placed downstream from Chicago. Options are being discussed as a way to keep the Asian carp at bay, like poisoning the fish by polluting the water, but that would kill other fish as well.

Some scientists favor a noise barrier, in addition to the electric barrier, that would repel the fish and get them to turn around. Rasmussen says the only long term fix might be to shut down the Sanitary and Ship Canal altogether, thereby establishing a permanent divider between the Great Lakes and Mississippi River watershed.

"Our strategy on the rivers now is to try and keep these things out of any reaches that they haven’t invaded so far," Rasmussen said. "Once a species gets out there in these kinds of numbers and this widespread, it’s virtually impossible" to get rid of them.

Fox News' Liza Porteus contributed to this report.