Like music to their noses, sea lampreys follow a chemical signal in rivers when it's time for them to migrate. And now, newly armed with the recipe for that signal, scientists hope to play Pied Piper by luring the eel-like parasites out of the Great Lakes, where they've wreaked havoc on fisheries for more than a century.
Sea lampreys spend much of their lives as filter-feeding larvae, but they grow up to become parasites, attaching onto fish and feeding on their blood. Once fully grown, the creatures look for spawning grounds. Rather than head back to their own birth streams, like salmon, lampreys sniff out tiny concentrations of a pheromone released by larvae.
That gave behavioral ecologist Peter Sorensen of the University of Minnesota an idea for new kind of pest control that might be an alternative to the pesticides currently used by Great Lakes fisheries managers. To identify the principal components of the lamprey pheromone, Sorensen and his team first isolated chemical compounds in lake water that had once held lamprey larvae. They then measured adult lampreys' olfactory responses to each fraction, ultimately identifying three compounds that generated a large response.
The lampreys responded most strongly to a previously unidentified steroid. They were able to detect the chemical signal at fantastically low levels: 500 grams of the compound would activate the entire flow of Niagara Falls for a month, Sorensen says. The lampreys were nearly as sensitive to two other compounds, one of which has a chemical structure similar to a component of the creatures' sex pheromone, the researchers report online 2 October in Nature Chemical Biology.
A pheromone control strategy likely wouldn't hurt other creatures, considering the species-specific nature of the chemicals, the tiny concentrations, and the fact that the chemicals are already present in the lake and stream water, Sorensen says. And, he adds, the beauty of using pheromones is that they should be effective for both conservation and management--ironically, there are places in the world where lampreys are highly prized as food, but the populations are threatened.
These findings have tremendous implications for lamprey control, says Chuck Krueger, science director of the Great Lakes Fishery Commission, which funded the research. “If we can direct them into a stream that is inappropriate for spawning, or to an easy place to gain access to them for removal, it could remarkably change how we conduct control,” he says.
Behavioral ecologist Michael Wagner of Michigan State University notes that synthesized pheromones probably won't replace lampricides altogether. "The goal is to direct them effectively to existing traps." Wagner plans to start field tests of the pheromones during the creatures' brief migratory period next spring.