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Great Lakes Article:

Scientists discover new way to control parasitic fish in Great Lakes
By Susanna Quick
Milwaukee Journal Sentinel
Posted on on October 3, 2005

MILWAUKEE - (KRT) - First they tried to block them out, erecting walls and barriers to prevent the slippery, eel-like bloodsuckers from migrating up rivers to spawn. But that didn't work.

Then wildlife officials tried to poison the exotic sea lampreys, dousing them with a toxic shower of chemicals as the toothy fish wriggled over their riparian spawning beds. But that practice provoked opposition and sometimes proved deadly for invertebrates and cartilaginous fish caught in the chemical cloud.

Now researchers believe they may have found a new tool to help control and reduce the population of Great Lakes sea lampreys.

Scientists at the University of Minnesota have identified and synthesized a powerful pheromone that may be used to lure large numbers of adult lampreys to their deaths. The research was reported in Sunday's online version of Nature Chemical Biology.

"I'd say this is pretty important stuff," said Henry Quinlan, a fisheries biologist at the Ashland fishery resources office of the U.S. Fish and Wildlife Service. "It's another potential tool for sea lamprey control. It's certainly exciting."

The Atlantic sea lamprey is a non-bony, parasitic fish that was first noticed lurking in Lake Erie in 1921. Now in each of the Great Lakes, the foreign pest has sucked fluids from fish such as lake trout, whitefish and herring, decimating and in some cases destroying these ecologically and commercially important fisheries.

For more than 50 years, wildlife officials have tried to control the situation. And while they believe they finally have a handle on the problem - with the use of the chemical TFM, a lampricide that selectively kills the creatures in the larval stage when applied to tributary streams - they'd like to do more.

This is where the new research comes into play.

Trained in the biology and physiology of fish-smelling, Peter Sorensen, a professor of fish biology at the University of Minnesota, started in 1990 to look at the lamprey's chemical and olfactory repertoire.

Nearly 400 million years old, lampreys, like many other ancient sea creatures, tend to rely heavily on chemical cues for communication. Indeed, the lamprey's "nose," or its sensory epithelium, exceeds the size of its brain.

Sorensen figured if he could identify the chemicals that the lampreys were using to call one another, he might be able use their own bodily secretions against them.

Sea lampreys reproduce in freshwater streams, where their larvae spend three to 20 years. Toothless and blind, the larval lampreys burrow into the river bottom, stretching their heads up into the current where they open their fleshy, hooded mouths wide to feed on the detritus that floats by.

At some point, they disengage themselves from their muddy holes and transform into free-swimming juveniles. During this metamorphosis, they lose their hood, grow eyes and develop a set of teeth on their tongue and "sucking disk" - a flat, disk-shaped area that surrounds their mouth.

Now called transformers, the silvery, pencil-length juveniles catch the current downstream to the lake, where they start sucking juice and blood from fish.

The average sea lamprey may kill as many as a dozen lake trout - totaling 40 pounds - during its one- or two-year stay in open water. The duration of attachment on a fish varies, but the site of attack, time of year and size of lamprey all help determine whether the assault will be fatal.

When the lamprey matures, it starts to seek out suitable rivers for spawning. Unlike salmon, which return to their streams of birth, lampreys look for streams that have suitable habitat.

This is where Sorensen's work comes in. It appears that the odor of healthy larvae attracts adults to specific streams.

The odor is so powerful, said Sorensen, that one of his graduate students discovered that a single larva could activate hundreds of gallons of water.

That fact alone indicated to Sorensen that this odor might be potent enough to attract adults in the massively diluted environment of one of the Great Lakes. The next step was to find out what the pheromone was.

He and students in his lab took larval-tainted water samples and removed chemical compounds within it. Sifting through these compounds, they isolated three they believed to be involved in the pheromone.

They were able to identify one of the compounds, but the other two were a mystery. So they contacted Thomas Hoye, a chemist at the university.

Hoye told Jared Fine, one of Sorensen's graduate students, that he'd need an ample amount of the pheromone to identify it.

"So, Jared rolled up his sleeves, and dug into 8,000 liters of water - that's 2,000 gallons - that had held 35,000 larvae. He came to me with a couple of samples, which weighed less than a milligram. That's the equivalent of 10 grains of salt," Hoye said. But it was enough.

They identified the compounds, and then needed to synthesize them.

They did that, but to make the chemical a useful management tool, they'll need to figure out a way to synthesize it more efficiently, Hoye said.

"Think of Lewis and Clark," he said. "They set out to find a way to get to the Pacific. They went down dead-end rivers and had to come back. But they got there, even if it wasn't the most efficient way. Somebody else had to come along and find a more effective way to get through to the Pacific_to get their carriages through the mountain range more easily."

That's the next step for Hoye and Sorensen - to figure out how to make large quantities of this chemical easily.

Sorensen said field work has already begun using the pheromone. Trials conducted by the Great Lakes Fishery Commission in Ann Arbor, Mich., started this summer. Fish managers discovered that the pheromone worked well.

Splitting a stream in two - one run laced with pheromone, the other without - they found that the treated side brought in as many as seven times the number of adults as the untreated run, Sorensen said. That research is not yet published.

It is believed the pheromone will be used to attract lampreys to specific streams and traps where they can be removed or poisoned. It may also become a useful conservation tool in areas of the Atlantic and North Pacific where the sea lamprey is endangered.

If the pheromone could be synthesized at reasonable cost, it might allow fisheries workers to virtually eliminate sea lampreys from the Great Lakes through intensive trapping, said Bill Horns, Great Lakes fish biologist for the Wisconsin Department of Natural Resources. Because the U.S. and Canadian governments spend more than $10 million a year to control lampreys by other means, and lampreys still damage fisheries, "that would be a major development," he added.

Hoye suggested that the trapped lampreys could be shipped to Finland and Portugal, where they are considered delicacies.

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