Scientists trying to fish out Asian carp from Great Lakes

Reporting from Chicago — 

The forecast was grim.

A parasitic invasive species that fed on healthy trout, salmon and catfish had entered the Great Lakes through its shipping canals, quickly asserted its dominance, and pushed commercial and sport fishing industries to the brink.

The sea lamprey, a razor-toothed, eel-like monster, attached itself to large fish and sucked the life out of them. In the 1940s, with no known predators and no clear road map to stop them, many feared the sea lamprey would take over the world’s largest freshwater body.

More than 50 years after biologists launched an all-out assault on the sea lamprey, the war is all but over. With science, money and muscle, biologists have reduced the sea lamprey population by 90% and restored the natural balance to the Great Lakes.

Now, many of the tools scientists used to save the lakes from the sea lamprey will be part of their defense against the Asian carp, the next in a long line of invasive species predicted to forever change the Great Lakes.

“When a lot of people say, ‘The game is over’ when it comes to Asian carp getting into the Great Lakes, I don’t think so,” said Michael Hoff, an aquatic invasive species expert with the U.S. Fish and Wildlife Service. “It’s a different game we play. But it’s not over.”

The U.S. Fish and Wildlife Service, in conjunction with the Great Lakes Fishery Commission and other agencies, has attacked sea lampreys on many fronts. The agencies dumped toxic chemicals into rivers and channels where sea lampreys spawn. They’ve erected barriers and reinforced existing ones to seal off sea lamprey from spawning beds. They’ve trapped male lampreys, sterilized them and placed them back into the water to fool female lampreys into spawning with them.

The goal was never to rid the Great Lakes of sea lamprey; it was to disrupt their reproductive habits enough to allow native fish populations to recover on their own.

Though scientists claim victory against the sea lamprey, it hasn’t come easily or cheaply. The federal government still spends between $20 million and $30 million a year to fight them, said Leon Carl, the Midwest regional executive of the U.S. Geological Survey. And they’re still experimenting with new ways to do it.

Researchers use pheromones to attract or repel sea lampreys, essentially moving them from one place to another. The technique has shown promise in lab tests, but has only recently been tried in the field, Hoff said.

If successful, pheromones -- seductive scents bringing male and female lampreys together -- could become a key weapon in eradicating Asian carp, Carl said. The U.S. Geological Survey began working on Asian carp pheromones about three years ago, but a lack of money stopped development before scientists could isolate the exact pheromone they wanted.

Thanks to millions of dollars allocated toward Asian carp research in the Great Lakes Restoration Initiative, that pheromone project will continue, Carl said, along with other ground-breaking endeavors.

Scientists are working with a private company to apply the fish toxin rotenone to a molecule that could be consumed only by filter-feeding fish like Asian carp. The method is similar to techniques used to deliver medicine to trout raised in hatcheries, Carl said. Officials hope to test the toxin in the field within 18 months.

This spring, scientists plan to begin experimenting with an underwater cannon that shoots pulses of compressed gas to disrupt Asian carp during spawning or to create a kind of underwater barrier that could prevent carp from passing through open navigational locks.

If successful, a larger rollout could happen by the end of summer, Carl said.

jhood@tribune.com