Taking Measures to Control an Invasive Species

At their peak in the 1960s, sea lampreys wiped out much of the sport and commercial fishing in the Great Lakes. "All the fish being stocked were coming out like Swiss cheese, with lamprey wounds," said Great Lakes Fishery Commission spokesman Marc Gaden.

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"It's not an exaggeration to say sea lampreys changed a way of life in the Great Lakes -- communities that relied on commercial fishing and people who liked sport-fishing -- the entire food web was altered," Gaden added.

Since then, chemicals called lampricides and electric barriers in the streams where lampreys spawn have cut the Great Lakes sea lamprey population from almost 3 million to about 433,000. But electric barriers and widespread lampricide use are not possible in the St. Mary's River, a broad, navigable waterway connecting Lake Superior and Lake Huron, which Gaden calls "the motherlode of sea lamprey spawning."

"Lampreys were building up there like an invading army going out into Lake Huron and knocking the stuffing out of the fish," Gaden said. "The sterilization program was the linchpin to getting them under control."

Lake Huron is thought to have the largest sea lamprey population in the region with about 157,000 spawning adults. But that number is about one-quarter of what it was at its peak, thanks to the sterilization program.

Sterilization of males, often through radiation, is used to control other pests, including mosquitoes, flies and rats. In larger animals, including possums and deer, females have been sterilized for population control. Gaden said boll weevil sterilization was the inspiration for the sea lamprey program, which started in 1991. He knows of no other aquatic sterilization program of a similar scale.

The sea lamprey's life cycle makes it well-suited for both targeted lampricide use and sterilization. Worm-like sea lamprey larvae live in the beds of streams and rivers from three to 17 years before their metamorphosis into the parasitic adult stage, which lasts about a year.

Finally the lamprey ceases eating and heads back to streams or rivers in springtime to spawn and then die.

To be effective, the sterile males released in St. Mary's River must outnumber fertile males 4 to 1. So sea lampreys trapped throughout the Great Lakes region are shipped on trucks to the USGS's Hammond Bay station, with 25,000 to 40,000 sterilized each summer.

Sterilization is being used only on the Lake Huron population, as scientists have not been able to capture enough males to overwhelm the breeding pools in other spots.

"We're already putting in all the ones we can get our hands on," said USGS fisheries biologist Roger Bergstedt.

They have considered farming male lampreys for the purpose of sterilizing them or importing males from the Atlantic Ocean, but both options seem too risky.

Sterilization is a welcome alternative to the chemicals TFM and Bayluscide that are used to kill sea lamprey larvae in several hundred Great Lakes tributaries. Those lampricides were selected for their minimal effect on other life forms, and are applied in carefully calculated amounts.

But some critics still worry that the substances could harm other organisms, including amphibians, young sturgeon and native freshwater lampreys, which are not an ecological problem.

"Anytime we can do something that eliminates or minimizes the use of chemicals, that's the preference," Bergstedt said. "And sterilization is more cost-effective than lampricides."

Gaden noted that out of about 180 invasive species currently inhabiting the Great Lakes, sea lampreys are the only ones that can be effectively controlled.

"It takes ongoing work and continued vigilance," he said. "But we can do it."