Aquatic Pied Pipers

By Eric Bland

Like the mythical Pied Piper who liberated a city from rats, a group of researchers have become aquatic Pied Pipers, trying to free the Great Lakes of a parasitic, alien species.  The researchers have isolated, identified, and synthesized a chemical attractant, or pheromone, that leads spawning adult sea lampreys to mating sites.  Using these pheromones, researchers hope to better control the parasitic lampreys, which have ravaged the Great Lakes fishing industry.

Michael Towhee, a Fisheries Biologist for the US Fish and Wildlife Service in Marquette, Mich., is excited about the new control technique.  “Field trials indicate that this is a very powerful compound.” 

Using the pheromone, capture rates of the boneless 400 million year old parasite are up six-fold.

"This is an entirely new and very appealing, environmentally safe and hopefully inexpensive way to control lampreys," said Peter Sorenson, one of the authors of the study, which appeared in the October 2, 2005 issue of Nature Chemical Biology.  Sorenson has been working with sea lampreys for nearly 30 years. 

“This is also the first migratory pheromone ever discovered,” Sorenson said.  Fish often use chemical cues to find food in murky and turbulent water and are extraordinarily sensitive to minuscule amounts.  One gram of the pheromone, called PADS, is enough to treat more than 5,000 Olympic size swimming pools.

PADS is produced by lamprey larvae.  Lampreys spend most of their lives as small larvae, burrowed into the muddy, silty bed of a stream eating algae.  Once they reach about 120mm in length they develop eyes, a mouth, and drift downstream to a large lake or the ocean to feed.

Adult lampreys are about 18 inches long, look like an eel, and have a toothy, circular mouth, which they use to suck out the body juices of fish.  They live for about 18 months, at the end of which they return to freshwater streams to mate and die.  They are not a threat to humans.

Currently the most effective way to control lampreys is an expensive and unpopular poisoning program.  Lampricide is trucked to streams with high concentrations of larvae and dumped in the stream, where it kills about 90% of the lamprey larvae, along with all other aquatic invertebrates, which can greatly disrupt a streams normal ecology.  The Great Lakes Fisheries Commission, which over sees all lamprey control efforts in the Great Lakes, also traps adult male lamprey, chemically sterilizes them, and releases them so they can compete with virile males for mates.

The GLFC hopes to use PADS in a couple of different ways.   They can lure mating lampreys to streams where there are no places for adults to lay their eggs, or to streams where the bottom isn’t suitable for lamprey larvae.  The researchers can lure adults into traps for the sterilization program or simply kill them.  The GLFC plans to use PADS for lamprey control across the Great Lakes Basin by 2010.

Lampreys invaded the Great Lakes in the 1920’s when new canals that connected the Great Lakes with the Atlantic Ocean were opened.  They decimated the Great Lakes fishing industry.  Even though PADS shows promise in controlling lamprey numbers, Sorenson cautions that “this will not revive commercial fishing in the Great Lakes.” 

PADS is also very similar chemically to an anti-cancer agent produced by the dogfish shark, called squalamine.  This suggests that pheromones might have been originally developed as a way to keep fish healthier, and were later adapted to help fish find their ways to important locations.  No trials have tested PADS’ medical potential.

While researchers in the Great Lakes are hoping to use PADS to kill lampreys, there are plans on the West Coast and in Europe to use PADS to help restore lamprey runs.  Lamprey is considered a delicacy in these regions and the fish have been nearly hunted to extinction.

Sorenson describes the taste of lamprey as “pretty gamey, strange, and I didn’t like it very much.”  While Sorenson doesn't like the taste, the lampreys certainly like the smell of PADS, and that could be good news for Great Lakes ecosystems.