Scientists to test new sea lamprey control on Michigan streams

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Capital News Service
LANSING — If the local river starts to smell like dead sea lamprey, you may be in luck. That smell could be the solution to a long-standing invasive species problem.
A new $392,000 Environmental Protection Agency grant will pay for testing sea lamprey repellant on three spawning streams in the state.
The project is expected to be completed within 10 years the EPA requires.

Sea lamprey attacking a lake trout. Credit: U.S. Fish & Wildlife Service

Sea lamprey are attracted to the smell of their young and repulsed by the stench of their dead, according to Michael Wagner, the lead researcher on the project and an assistant professor of fisheries and wildlife at Michigan State University.

Those facts are key to controlling the troublesome invasive species, he said.
Sea lamprey are parasitic, eel-shaped fish that attach to larger fish with suction mouths. Their sharp tongues lash their prey and they feed on the blood of their victims, which then often die from blood loss or infections.
Left unchecked, lamprey threaten both the ecosystem and commercial fishing in the Great Lakes, Wagner said.
What makes them easy to manipulate is that they rely on chemical information from pheromones above all other senses, Wagner said.
“The lamprey are basically a swimming nose,” said Marc Gaden, the communications director for the Great Lakes Fishery Commission, a joint U.S-Canadian agency based in Ann Arbor.
Charged with maximizing favorable fish, the commission has worked to control lamprey since the 1950s. It spends about $22 million a year on research and control programs.
Lamprey larvae are blind and live in streams for four to six years before growing teeth and heading into the Great Lakes to suck fish blood. Eventually, they return to reproduce.
But unlike salmon, they don’t return to the same stream they were born in. Instead, they rely on the smell of lamprey young to guide them.
Adults die after spawning and the only way they can protect their young is to leave them in a safe area. That’s why they’re attracted to the smell of lamprey young, Wagner said. Any stream with that smell should be a good place for the young to survive.
Usually, they encounter the dead lamprey scent if they swim past a breeding ground that was hit hard during the winter. The larvae freeze, and when spring comes, they defrost and decompose, signaling other lamprey via scent that the neighborhood is no longer a good place to raise their young.
And while that’s not a conscious decision, it’s certainly a logical adaptation, researchers say.
They’re choosing neighborhoods based on how many other larvae have survived there, Wagner said. “How do your parents pick the neighborhood they want to raise you in?”
As long as there are surviving lamprey larvae, chances are it’s a good place.
Lamprey faced with two streams with a favorable odor won’t necessarily choose the one with the stronger smell, Wagner said. Even if the odor is 10 times as strong in one direction, lamprey don’t care.
That’s where researchers hope the dead lamprey scent can play a role by blocking each diverging stream. If they can corral all the lamprey in a few selected spots, it’s easier to kill them because it’s too costly and labor-intensive to control all potential habitats.
Lamprey are active primarily at night, so researchers know exactly when to apply the repellant.
That’s good, Wagner said, because if the repellant were constantly present, lamprey would get used to it and ignore it.
“This becomes a bit of a game of Whac-A-Mole,” Wagner said. “So how do you win a game of Whac-A-Mole? The only way to do it is to plug some of the holes.”
The tests, if successful, will bring control closer to what Wagner calls the ideal: a program where sea lamprey can be targeted without damaging the rest of the ecosystem.
Instead of poisoning multiple rivers and potentially harming many species, damage will be dealt almost exclusively to lamprey populations.
“If this works, you’ve achieved the holy grail of government environmental management programs,” Wagner said. “You’ve managed to make the program more efficient without increasing the cost.”
Controlling invasive species is often a matter of diminishing returns. Eradication has proven difficult, and the fewer the lamprey, the more it costs for each additional fish kill.
But if Wagner’s research program is successful, savings could be high, according to Gaden.
For example, he said using that method on a small stream could save between $50,000 and $100,000 every four years by reducing the amount of pesticides used and the time spent hunting down lamprey breeding grounds.
In the case of larger rivers, like the Manistique River, savings would rise dramatically.
“You’re talking about saving in the neighborhood of half a million to a million dollars every four years,” Gaden said.
Larger rivers will most likely require a combination of methods, including the repellant, traps and a physical barrier, he said.
Wagner said that a sudden drop in lamprey populations would likely not affect native fish because numbers are already down 90 percent from their historical high point in the 1930s, when they crashed commercial fisheries.
Despite their lowered numbers, they continue to cause damage, he said.
“The goal of the program is to get that damage down to the point where economic and ecological harm is minimalized.”
He said the three Michigan test sites haven’t been chosen yet.

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