Though sea lampreys may be known for their sharp, pointy teeth, their sense of smell is highly sensitive.

Though sea lampreys may be known for their sharp, pointy teeth, their sense of smell is highly sensitive.

T. Lawrence/ GLFC

So long suckers! Sex pheromone may combat destructive lampreys

With their suction cup mouths filled with concentric circles of pointy teeth that suck the body fluid of unsuspecting victims, lampreys may seem like the stuff of horror movies. And indeed the 50-centimeter-long, eellike creatures can wreak havoc on freshwater communities when they invade from the sea, with a single sea lamprey able to kill 18 kilograms of fish in its lifetime. Now, the U.S. government has approved of a new way to combat these fearsome fish by using their own sense of smell against them.

Sea lampreys are a particular problem in the Great Lakes regions of the United States and Canada. They hitchhiked into the region more than a century ago, likely attaching themselves to ships or fish that traveled along shipping channels from the Atlantic Ocean. Although most lampreys are mere parasites in their native habitats, those in the Great Lakes are far worse, says Nicholas Johnson, a research ecologist at the U.S. Geological Survey’s Hammond Bay Biological Station on Lake Huron in Millersburg, Michigan. “They kill their host, they get too big, they eat too much,” he says. “They’re really more of a predator.” After the toothy invaders proliferated in the mid-20th century, ecosystems all but collapsed, taking prosperous fishing and tourism industries with them.

“It’s fair to say that lamprey[s] changed the way of life in the region,” says Marc Gaden of the Great Lakes Fishery Commission, a joint U.S. and Canadian organization based in Ann Arbor, Michigan, that’s tasked with managing the rebounding ecosystems. “Just about every fishery management decision that we make to this day has to take lamprey into consideration.”

For decades, the fishery commission and a team of scientists and advocates across the public and private sectors have been developing measures to control sea lamprey populations. Dams prevent lampreys from reaching mating grounds, chemical lampricides wipe out larvae, and officials use traps to pull lampreys out of the environment and kill them.

The newest measure involves hijacking a sex pheromone that male lampreys use to attract females. A few years ago, Johnson demonstrated that baiting lamprey traps with the pheromone, called 3kPZS, increased trap efficiency by 10% on average, and in some streams more than 30%. Females can detect pheromones at distances of at least 2 kilometers and are lured to traps expecting a sexual encounter, while males are left with fewer mates.

The latest milestone came in December 2015, when the U.S. Environmental Protection Agency officially registered 3kPZS as a “biopesticide”—upgrading the naturally occurring, nontoxic chemical from its classification as an experimental substance and approving it for use in the environment. It’s the first biopesticide approved to control vertebrates, many others are already in use to combat gypsy moths, beetles, and other pesky insects.

Thanks to the suite of control measures already developed, sea lamprey populations are 90% lower than their peak populations were 60 years ago. But those measures all have limitations: Dams block more species than just lampreys, lampricides are only effective in certain environments, and traps don’t discriminate which individuals they catch. Officials hope 3kPZS can fill in the gaps where other tools fall short. “Any good pest management does not rely on any single technique,” Gaden says.

Jennifer Nalbone, an environmental scientist who advises the Great Lakes Fishery Commission but wasn’t involved in developing 3kPZS, says that developing new tools will always be important, no matter how much progress is made. “There’s always the concern that ecosystems change and species adapt,” she says—and the stakes are high. “You let go for a year and it takes a decade to regain that ground.”

Robert McLaughlin, a fish ecologist at the University if Guelph in Canada who was not involved in 3kPZS development, agrees the biopesticide shows considerable promise. But he cautions that it’s too early to really know how effective it will be in the environment.

Gaden says it could still be a few years before 3kPZS is ready to be used everywhere sea lampreys are a problem in the Great Lakes. Researchers need to scale its production up and determine the environments in which it works best, and Canadian regulatory agencies are still reviewing the biopesticide for use on their side of the Great Lakes. In the meantime, Johnson and his colleagues are exploring the potential of other pheromones that might be used as repellants.