A Lamprey Love Triangle

This is a tale of blood-sucking invaders and sex traps.

June 29, 2015

Photo: T. Lawrence/Great Lakes Fishery Commission

Aaron Jubar electrocutes baby fish for a living. He carries an electric wand in a backpack as he wades through rivers and streams that flow into the Great Lakes, and when he comes across sea lamprey larvae … zap!

Amusing stories of lampreys falling from the sky have been making headlines over the last month or so, but invasive sea lamprey in the Great Lakes are no joke. That’s why Jubar, a biologist for the U.S. Fish and Wildlife Service, and an army of other wand wielders walk the lakes’ tributaries between April and October.

With a circular mouthful of teeth reminiscent of the monster from Alien, sea lamprey latch onto lake trout and begin sucking the life out of them. They bite the fishes’ sides, sinking their teeth and sharp tongues into the flesh before they drain them of blood and other fluids. The fish often die as a result.

Photo: Ted Treska/USFWSA lake trout with severe sea lamprey wounds

Lake trout are among the top predators in the Great Lakes but lamprey decimated their population last century, leading tribal, state, and federal governments from both the United States and Canada to form the Great Lakes Fishery Commission. In the forties, American and Canadian fishermen were bringing in about 15 million pounds of lake trout each year from the upper Great Lakes. By the 1960s, the harvest had crashed to around 300,000 pounds—just 2 percent of the previous catches.

“Back in the 1930s and ’40s, as lampreys were having their way in the Great Lakes, fisheries managers were freaking out,” says Michael Twohey, another fish biologist with the service and a 37-year veteran of the commission’s sea lamprey program. Since then, the program, with an annual budget of $20 million, has had great success, killing off about 95 percent of the invasive parasites. But lamprey still slither and suck within the Great Lakes ecosystem, and with a single female producing about 100,000 eggs in her lifetime, that remaining 5 percent is still quite a threat.

The most effective efforts so far have focused on attacking the fish in its larval stages. Starting in the late 1950s, applications of a lampricide that targets only lampreys helped kill off most of the parasites. Sea lamprey, unfortunately, are moving targets. These hitchhikers don’t return to the same streams to spawn, making them difficult to find. That’s why Jubar wanders the tributaries with an electric wand, and why researchers are trying a new strategy: diving into the realm of sea lamprey sexual frustration.

Lamprey release sex pheromones whenever they reach a stream where they can spawn, essentially telling other lamprey, “Hey! Good conditions ahead!” Once researchers parse out which of the 6,000 or so chemicals present in the pheromones are the most potent, they could use them to attract and trap the fish. In addition, when lamprey die, their decaying bodies release necromones, which may dissuade other sea lamprey from going to that area. Together, these baits and repellants form what fisheries managers call their push-pull strategy.

“Pheromones are typically a complex cocktail,” says Twohey. Scientists have made great strides since the research began in the 2000s, but they better hurry up to find the right concoctions of lamprey perfumes.

Plans to remove dams in Great Lake tributaries have gathered steam in recent years, which is great news for water quality and migratory fish like steelhead trout. “Unfortunately,” says Jubar, “the darker side of stream connectivity is that you can promote increased infestation of sea lamprey.”

Removing the dams could create freeways for all sorts of invasives and give lampreys new places to sink their teeth upstream. Before those barriers are taken down, the commission wants its control programs in place to give any pioneering lampreys a rough welcome.

Because that pesky 5 percent of the remaining lamprey population is still out there, waiting for whatever comes first—a juicy lake trout, a dose of sexual sabotage, or … zap!

onEarth provides reporting and analysis about environmental science, policy, and culture. All opinions expressed are those of the authors and do not necessarily reflect the policies or positions of NRDC. Learn more or follow us on Facebook and Twitter.

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