By Howard Meyerson
Scientists studying sea lamprey behavior are testing a new way to keep them out of Michigan rivers. An experiment on the Ocqueoc River by Michigan State University researchers this summer found nearly all of 350 radio-tagged lampreys avoided a stretch of river where researchers released a compound derived of dead lampreys.
The findings affirm what researchers have seen in laboratory studies so far. The study is part of an $181,000, three-year project funded by the Great Lakes Fishery Commission.
“They completely avoided the odor,” said Mike Wagner, assistant professor in the Department of Fisheries and Wildlife at Michigan State University and the lead researcher for the project. “Our prediction was they will swim on the opposite side. That is what we saw. It didn’t keep them from moving upstream, but they don’t move through it. Only one went through and we think there might have been a gap (in the scent) because of an eddy.”
Scientists call the compound an “alert-cue” or “necromone,” a chemical in the lamprey body that is released when it dies. Studies of fish have long shown similar reactions among their own, but this is the first study to focus on lampreys which rely extensively on their sense of smell. Lamprey move primarily at night when visibility is at its worst, Wagner said.
“We think the odor tells them to avoid the area,” Wagner said. “There are three circumstances that they smell dead lamprey. Those are in early migration before they spawn and it probably indicates that lamprey are being killed by predators like raccoons. It tells them they need another stream.”
Lamprey might encounter necromones if lamprey larvae, which burrow into streams, do not survive the winter and begin to decay come spring. That smell would signal the need to spawn somewhere else, according to Wagner. Smelling it late in the spawning migration could signal that the early spawners are dead and no mates are to be found.
Wagner and other researchers think necromones might one day be used as chemical barriers in the war against sea lamprey. If studies continue to show positive results and cost-effective production methods can be found, it could be used to keep sea lamprey out of high-quality streams, or branches of rivers that have good spawning habitat.
“If you can use an alarm cue to shut off a stream with good spawning habitat and attract them to streams with poor spawning habitat (with a chemical attractant) , they will waste the effort and not as many will survive,” said Mike Siefkes the sea lamprey program specialist with the Great Lakes Fishery Commission and co-investigator for the study.
“On the best streams we can trap 60 to 70 percent of the lamprey, but on other challenging streams we only get 10 percent. If we could make them go up streams where we could capture them more easily or kill more with lampricides, it makes the program more efficient.
“It’s why the commission is excited about this. Things worked very well in the stream experiment this summer and it looks very promising,” Siefkes said.
Sea lamprey are found in 475 Great Lakes tributaries, according to Siefkes, fully 9 percent of 5,300 streams in the basin. Those streams are treated with a chemical lampricide, every three to 10 years depending on the population size and growth rates. The chemical, TFM, has been used since the 1950s. It targets young sea lamprey larvae that burrow into stream bottoms. TFM treatments may kill 95 percent of the larvae, but not always, according to Siefkes.
“In challenging areas, it is only 50 to 60 percent effective,” he said. “We have reduced lamprey 90 percent from the peak levels of the 1950’s and 1960’s, but we are still above target for each of the Great Lakes.”
The Ocqueoc River experiment was the first field test of the theory. Necromones were released down one side of the river while a control odor was released along the other shore. Future research will focus also on the role that odor plays in the lamprey life cycle. Wagner has applied for a three year, $393,000 grant from the U.S. EPA to demonstrate that the method can be used for two years for full-scale control of two other rivers.
“The approach is a push-pull (block them on some and attract them up others),” Wagner said. “If we can get them to concentrate their reproduction in smaller areas, it makes the lampricide program more effective without increasing costs. Those savings can be applied to other areas that need treatment.
“The second benefit is that it minimizes harm and maximizes benefits for the ecosystem. If we can guide their movement we can guide them away from streams that we don’t want to use pesticides, like sturgeon habitat and high-quality streams.”
On the web:
MSU Videos: Lamprey’ Panic in the laboratory
Copyright © 2012 Howard Meyerson