Biologists battle killer in the Great Lakes

Control of sea lamprey has allowed a rebirth of commercial fishing on Lake Superior

July 6, 2011

by Catherine Winter

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A lot of people are worried about Asian carp swimming into the Great Lakes. We know from experience how bad an invasive species can be. Sea lamprey devastated the Great Lakes fishery in the 1940s and 50s, and they still kill a lot of fish.

Sea lamprey are native to the Atlantic Ocean. They swam into the upper Great Lakes through ship canals. Now that they’re here, they can’t be eradicated; they can only be reduced in number, and that’s a constant battle.


“It’s kind of a whack-a-mole situation,” says Don Schreiner, area fisheries supervisor for Lake Superior for the Minnesota DNR.Federal, state, and Canadian government agencies cooperate on sea lamprey control. Schreiner says they’ve tried cutting back efforts on some lakes.

“We thought we had them under control,” he says. “We moved that control to another lake that needed more help, and sea lamprey just blossomed where we moved the control away from.”

Sea lamprey swim up rivers to reproduce, so many of the tributaries into the Great Lakes have lamprey barriers now. Fish ladders allow other fish to pass, but sea lamprey can’t get over them.

On a June morning, Tom Davies visited the barrier on the Brule River in northern Wisconsin. Davies is a seasonal worker for the US Fish and Wildlife Service. One of his jobs is to climb down into a trap on the side of the barrier in hip waders and use a net to scoop out the sea lamprey that have been trapped that day.  Davies says some days, there are as many as 600 sea lamprey in the trap.

“You come down off the ladder and you’re literally stepping on them, and they’re swimming all around you, hitting you in the waders,” he says.

Davies says he and his coworkers have joked that the TV show “Fear Factor” should have had people in swimming suits climb into the trap. It would have been horrifying. Adult sea lamprey are a foot or more long, gray and slimy looking. They look like eels, but a sea lamprey’s head ends in a big, round suction cup mouth, filled with rows of teeth. They kill fish by latching onto them, rasping a hole, and sucking out the fluids.

Davies grabs a sea lamprey and lets it latch onto his bare arm. He has to pry it off.

“See the mark they leave so quick?” he asks. There’s a red ring on his skin.

Workers at the barriers measure and sex the lampreys. The males are saved for one of the control projects. They’re sterilized and released in the St. Mary’s River, between Lake Superior and Lake Huron, where they compete with fertile males and reduce the number of fertilized eggs.

Workers also apply a chemical to streams where sea lamprey spawn to kill the young.

The Minnesota DNR’s Don Schreiner says these control efforts cost $20 million a year, “and that’s funding we continually fight for in Congress.” It’s on the books to be reduced by 20 percent in 2012.

Schreiner says the Great Lakes’ fishery depends on sea lamprey control. Estimates of the worth of that fishery range as high as $7 billion. Most of that economic return comes from sport fishing, but commercial fishing is important to the Great Lakes region, too.

Even on Lake Superior’s north shore, where the water is cold and deep and doesn’t produce a lot of fish, a small commercial fishery has made a comeback.

In the early 20th century, there were more than 400 commercial fishermen on the Minnesota shore of Lake Superior. But overfishing, pollution, and sea lamprey devastated the fish population. Today, some of that pollution has been cleaned up, fishing has been restricted, and some fish are stocked. Fish such as lake trout and cisco have rebounded. But the state is being conservative, and will only license 25 commercial fishermen.

Most of those fishermen also do something else for a living. But fisherman Stephen Dahl says he’s not part of a vanishing breed.

“There’s definitely a perception that we’re the last of the Mohicans, we’re dying out,” Dahl says. “And it’s like, no, it’s changed. It’s a changed world.”

Dahl heads out into the big lake in a small, open boat every morning, unless there’s too much ice in the harbor for him to break through. He hauls nets from the depths by hand. It’s hard work. Some days the lake is rough and the wind howls. He laughs when he’s asked about being wet and cold.

“I think I was born wet and cold,” he says.

Dahl is only allowed to catch cisco, which North Shore fishermen refer to as lake herring. In other parts of the lake, it’s legal for commercial fishermen to take trout and whitefish. They’ve got a ready market. Restaurants and delis on the shore snap up the fish when they’re available. Sometimes, when people know the fish are running, they’ll come to the dock and buy the fish right from the fishermen.

“This whole local food movement is really good,” Dahl says. It’s increased demand. “Most of the time I can’t keep up.”

The local food movement helps support an apprentice Dahl recently trained. Dahl’s apprentice, Jason Bradley, now has his own master’s license and his own boat. He’s also co-owner of a community supported agriculture (CSA) farm. His customers get the usual box of vegetables, but they can also get a herring share.

Customer Mark Gordon co-owns a charter sailing business, and likes to serve his customers local food. He’s a big fan of Jason Bradley’s herring.

“You just feel good eating the fish when you know it’s come right out of the lake,” Gordon says. “There’s no question about where it’s come from and how it was processed.”

Lake Superior fish is also sold around the country, and even overseas. Some of it goes to Iowa and is made into gefilte fish. Some of the roe goes to Scandinavia.

Native fish have bounced back in Lake Superior, but the DNR’s Don Schreiner says it’s still a “precarious situation.”

Schreiner says control measures keep sea lamprey numbers down to about 5 to 10 percent of what they were at their height.

“It sounds like we’ve done a good job, and we have,” Schreiner says. “Except that sea lamprey are very efficient.”He says biologists estimate that sea lamprey still kill as many fish in Lake Superior as sport and commercial fishing combined.