You might be used to targeting invisible pollutants—dissolved metals, say—or more readily apparent things like sediments and nutrient-caused algae blooms. But it’s a safe bet that nothing else you’ve dealt with looks quite like this. The Great Lakes are having a lamprey problem.
As this New York Times article vividly describes, “Lampreys look like the stuff of horror films: a slithering, tubular body topped with a suction-cup mouth ringed with row upon row of hooked yellow teeth. With this mouth, a sea lamprey anchors to its fish prey and uses its rasping tongue to drill into the victim’s flesh. It remains there for up to a month, feeding on blood and body fluids. Even if a fish survives the attack, the gaping wound left behind often results in death.”
Many non-native species have invaded the Great Lakes—the Asian carp, the zebra mussel, the small herring known as the alewife. Lampreys are especially costly, as they can decimate fisheries. The Great Lakes Fishery Commission, which was founded in the 1950s largely to deal with the lampreys, spends $20 million a year to control them.
The lampreys arrived in Lake Ontario through the Erie Canal in the mid-1800s and in less than 100 years had spread throughout the Great Lakes. They have no natural predators in this environment, but plenty of food. As the Times article notes, at one point they were killing more than 100 million pounds of fish each year and drastically reducing harvests of lake trout, whitefish, and other species.
Researchers with the Great Lakes Fishery Commission tested thousands of chemicals to find something deadly to lampreys but more or less benign to other fish. They found a larvicide that works, and that—along with other measures like physical barriers—has greatly reduced the parasites’ numbers. But broadcasting this “lampricide” around the ecosystem is expensive and sometimes results in collateral damage to other species.
For some time now, they’ve been experimenting with synthesized pheromones to lure the lampreys to a concentrated area where they can be trapped or killed en masse. Lampreys choose where to spawn based on the scent of already-existing larvae that are buried in the mud. As Michael Wagner, a fish ecologist with Michigan State University, explains in the article, “It’s like choosing where to raise your kids based on a neighborhood’s crime rate and quality of schools. The odor larvae release says, ‘We’re thriving here.’” Scientists are using the scent of larvae to attract the lampreys in one direction, and they’re also using a scent based on dead or decaying lampreys in other areas to drive the lampreys away, essentially creating traffic patterns that allow them to achieve the same results with less application of poison.
Similar scent-based techniques have been used on insects but never before on vertebrates. Although it’s still in the research stage, a member of the Great Lakes Fishery Commission says, “This is the beginning of what could potentially be a new era in invasive species control.” If it’s successful, the pheromone technique could also be used to help lampreys in their native habitats where populations are declining because of habitat degradation.