A Breakthrough in Controlling Invasive Fish
On a windy July morning on Lake Superior’s Whitefish Bay, fisherman Ralph Wilcox of the Sault Ste. Marie Tribe of Chippewa Indians and his son, Dan, netted 300 pounds of wriggling whitefish. The mild-flavored salmon relative is served in restaurants, in smoked fish spreads, and as gefilte fish at Passover. However, two of the fish in the Michigan fishermen’s nets were badly wounded.
“They weren’t going to live much longer,” Wilcox said.
The wounds were the work of an aggressive invader: the sea lamprey. An Atlantic Ocean fish that is not native to inland lakes, sea lampreys use suction-cup mouths crammed with rasping teeth to latch onto larger fish and suck out bodily fluids. By traveling up shipping canals, sea lampreys reached all the Great Lakes by 1939. Big ocean fish can survive lamprey attacks; the abundant, vulnerable prey of the Great Lakes cannot.
Sea lampreys could devastate the Great Lakes commercial and recreational fisheries, which produce $7 billion a year in shared benefits to the U.S. and Canadian economies. In the 1950s, lampreys wiped out the lake trout that were tribal fishermen’s mainstay. Ralph Wilcox’s father and grandfather worked harder and earned less, switching from valuable trout to herring that sold for barely 4 cents a pound.
Federal scientists designed the first weapons used to fend off lampreys for the Great Lakes fishing industry. Researchers tested more than 6,000 chemical compounds and discovered two that kill sea lamprey larvae without significantly harming other aquatic life.
Applied to the gravelly streams where lampreys spawn and larvae develop, during the right season, “the treatment is 90 percent successful,” said U.S. Geological Survey (USGS) research biologist Michael Hansen. “But that remaining 10 percent is more than enough to repopulate the ecosystem. That’s why we need a variety of methods to control lampreys.”
Hansen supervises the USGS Hammond Bay Biological Station in Millersburg, Michigan, where the first lamprey-control compounds were developed, and new ones are in the works. “This station is where everything starts,” he said. “The techniques we develop here will be put to use throughout the Great Lakes.”
In an impressive bit of sleuthing, a team of USGS and academic researchers recently sifted through the myriad trace chemicals in the region’s freshwater ecosystems to identify the natural chemical signal, or pheromone, that male lampreys give off when ready to spawn. Female lampreys detect the pheromone and follow its scent to the males.
USGS research ecologist Nicholas Johnson led the field-testing of a lamprey mate-signaling pheromone named 3kPZS that was isolated and identified at Michigan State University. In late 2015, the Environmental Protection Agency registered 3kPZS as safe for use in nature, making it the world’s first pheromone for biological control of a fish and opening the door for control methods that use invasive animals’ own pheromones to trick them.
Experimental traps baited with 3kPZS capture up to 50 percent more female lampreys than unbaited traps. Johnson said researchers can also measure the natural pheromone in streams to find lampreys, then use traps, low-voltage electric fields, and other techniques to control them.
“But the best approach may be to block their ability to smell the pheromone in the first place,” Johnson said. In the lab, scientists plugged lampreys’ noses with latex. Lampreys that couldn’t smell had little chance of finding spawning sites or mates. Researchers are looking for a chemical that permanently blocks lampreys’ ability to smell pheromones—“a molecular way to plug up their noses,” Johnson said.
“We’re getting pretty modern, and it’s paying off,” said Ralph Wilcox, who links the survival of his family’s fishing business and restaurant in Brimley, Michigan, to the government’s success at controlling sea lampreys.
The innovation at the USGS Hammond Bay laboratory is unique in the world, said Hansen. Nowhere else have scientists identified a pheromone produced by an invasive fish and turned it against the invader. Once field tests are complete, fisheries managers from the States and the U.S. Fish and Wildlife Service can use it for fuller ecosystem restoration in streams where existing lamprey control techniques don’t work. Hansen believes the technique could lead to controls for other species wreaking havoc in U.S. waterways, such as the Asian carp.
Sea lampreys once killed nearly 103 million pounds of Great Lakes fish per year. Today, according to the Great Lakes Fishery Commission, lampreys kill less than 10 million pounds a year.
Hansen wants to get that estimate down to zero pounds. “We know sea lamprey eradication is an elusive goal,” he said, “but it’s best for the fishery and best for the Great Lakes ecosystem, and it should be our goal.”
For more information, please contact Anne Kinsinger, USGS Associate Director for Ecosystems, at akinsinger@usgs.gov.
Read more stories about USGS science in action.
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