By Elizabeth McGowan
Cold water rushes over gravel and stones as the river winds through forests and wetlands before joining the vast waters of the Great Lakes.
Beneath the rippling surface, an ancient predator begins its yearly search for a mate in the spring. The sea lamprey (Petromyzon marinus), a leach-like parasite, slinks through the predator-free water, sniffing out a mate.
The invasive species has long been a threat to Great Lakes fisheries.
“They look like a giant leech that has a suction-type mouth that attaches to fish and drinks their blood,” said Nicholas Johnson, a supervisory research ecologist with the U.S. Geological Survey at Hammond Bay Biological Station in Millersburg, Michigan.
Today’s control program relies primarily on lampricides, which kill sea lamprey larvae in streams, and barriers that block adults from reaching spawning habitat. These methods have been highly effective, but they aren’t perfect.
In some rivers, factors such as water chemistry, difficult terrain or limited access can make lampricide treatments and barriers harder to apply.
In those cases, alternative strategies could help fill the gaps.
Researchers are now exploring a new approach focused on something far less visible: the chemical signals lamprey use to find each other.
A recent study in the Journal of Chromatography B examined how chemicals that disrupt sea lamprey pheromones could one day help control their reproduction.
Instead of directly killing sea lampreys, the idea is to interfere with their ability to locate mates, thereby managing population levels, the study says.
Weiming Li, a professor at Michigan State University and one of the study’s authors, researches the chemical language of pheromones that lampreys use to communicate.
“What we are trying to do is develop a fundamental understanding of the mechanism and then either strengthen that mechanism or interrupt it,” Li said.
For sea lampreys, pheromones are essential. Males release a chemical signal that travels downstream, guiding females upstream for spawning.
These signals are highly potent, and lampreys can detect them at extremely low concentrations.
“ You don’t need much if you know exactly what chemicals act as pheromones,” Li said.
Johnson, who was not involved in the study, described lampreys as animals that rely almost entirely on smell to navigate their reproductive lives. In the vast rivers that flow into the Great Lakes, finding a mate is no easy task.
Lampreys are “almost swimming noses,” Johnson said, using scent cues to locate each other across long distances.
That sensitivity is exactly what makes pheromone research attractive to scientists. If researchers can interrupt that chemical communication, they may be able to stop reproduction before it starts.
The new research focuses on compounds known as pheromone antagonists. These chemicals interfere with the normal pheromone signal, making it harder for females to detect males.
In practice, pheromone antagonists would target the reproductive stage of the sea lamprey life cycle. Females entering a river would have difficulty detecting the chemical signals released by males, reducing the likelihood that they successfully spawn.
Sea lampreys die after their reproductive stage, so removing the ability to spawn could greatly reduce populations.
Anne Scott, a study co-author and a professor at Michigan State University, views this work as part of a broader effort to expand the tools available to fisheries managers.
“There is a long history of sea lamprey control,” Scott said. “Our work fits into it by identifying additional tools that can supplement those existing tactics.”
For Johnson, one of the most exciting aspects of pheromone-based control is its precision.
He said, “If it works, it could have very little impact on non-target species.” Native lampreys aren’t the villains – in fact, they clean streams through filter feeding and gravel movement and are beneficial to the ecosystem.
Still, researchers like Scott emphasize that pheromone antagonists are not a “silver bullet.”
Success relies on adaptive and evolving measures, not a one-and-done management technique, she said. Sea lampreys are resilient animals with complex life cycles, and controlling them requires multiple strategies working together.
Rather than replacing existing tools, Scott says pheromone-based approaches would likely work alongside them.
“I don’t think traditional control approaches are going to go away,” she said. “We’re looking for ways to supplement or augment those tactics.”
That message echoes across the sea lamprey control community. The program has succeeded for more than half a century largely because it combines science, management and international cooperation, according to the Great Lakes Fishery Commission .
Control is coordinated across agencies in the United States and Canada through the commission, bringing together researchers, managers and policymakers to address the invasive species.
Scott says that collaboration is essential to developing new approaches.
“There are researchers in labs contributing to these efforts, but also partnerships with agencies that implement control on the ground,” she said.
The stakes are high. The Great Lakes fishery is valued at more than $5 billion annually, according to the commission, supporting commercial fishing, recreational angling and tourism throughout the region.
Even people who never pick up a fishing rod are connected to the outcome.
“Sea lampreys can degrade the entire ecosystem,” Scott said. “If the fish community is impacted, that affects the health of the Great Lakes more broadly.”
For scientists like Li, the research is also about understanding one of the most ancient groups of vertebrates on Earth. Lampreys have existed for hundreds of millions of years, evolving sophisticated ways to navigate their environment.
By studying the chemistry behind those behaviors, researchers are not only uncovering new management tools but also learning how these animals communicate and survive.