Revolting sea lamprey an environmental success story [UPDATED]Published 7:25am Tuesday, July 10, 2012 Updated 11:28am Tuesday, July 10, 2012
By Dan Kraker
Minnesota Public Radio News
Near Lake Superior — Northwest Wisconsin’s Brule River is revered by anglers for its steelhead and trout fishing. But the picturesque stream that tumbles northward into Lake Superior provides great habitat for more than just sport fish.
Each spring, thousands of sea lamprey head for the Brule to spawn. Many of them are trapped on their way upstream by a low concrete dam that spans the river.
“It was put here just for keeping the lamprey out of the upper reaches of the river,” said Bill Mattes, who has helped trap and control sea lamprey for 17 years.
The sea lamprey was one of the first non-native species to invade the Great Lakes, and it’s been one of the most destructive. The eel-like parasite nearly wiped out the entire lake trout population. But in one of the rare success stories about exotic species, scientists have devised ways to keep the blood-sucking fish in check. That has allowed lake trout to make a historic comeback.
Next to the dam, Great Lakes Indian Fish and Wildlife Commission fisheries aid Acorn Armagost lifts a grate from the top of a big concrete pen next to the dam. Water flowing down a series of steps allows jumping fish to swim upstream, but lamprey can’t make the climb and are trapped.
Mattes, Great Lakes Section Leader of the Great Lakes Indian Fish and Wildlife Commission, watches his co-worker descends a ladder, scoops out a netful of the slithering, snake-like creatures, dumps them in a bucket, and grabs one.
A pointy tongue sticks out from the middle of a round mouth, about the size of a half dollar, filled with concentric rings of yellow hook-like teeth.
Tom Davies, a U.S. Fish and Wildlife Service technician, takes the lamprey and gently presses its mouth to the palm of his hand. He lets go and it dangles upside-down, its mouth suction-cupped to his hand.
“You can see that the teeth, they’re a work of art as far as being able to latch on to something and really just stick,” Davies said.
If you were to press the lamprey’s mouth to your hand, it wouldn’t hurt. But it’s weird, and unnerving. And, worse, the thing doesn’t let go, so you’d have to shake the lamprey off. But the sea lamprey is not a danger to humans, as it only preys on cold-blooded creatures.
It is, however, a danger to native species. A single adult lamprey can grow as big as five pounds and literally suck the life out of 40 pounds of Lake Superior fish in a single year.
Lamprey were first discovered in Lake Superior in 1939. A new canal bypassing Niagara Falls allowed them to migrate all the way from the Atlantic Ocean, said Marc Gaden, communications director for the Great Lakes Fisheries Commission, which oversees the lamprey control program.
Gaden said sea lamprey quickly decimated the lake trout fishery.
Over about two decades, the lamprey wiped out the lake trout in the lower four Great Lakes. In Lake Superior, only a few remained.
Scientists began frantically searching for a way to control lamprey. They struck gold in the 1950s when they discovered a chemical called TFM kills lamprey larvae while they’re still the size of earthworms, before they swim into the Great Lakes and begin preying on fish.
Thanks largely to TFM and traps and barriers like the one on the Brule River, 90 percent of the lamprey in Lake Superior and the rivers that feed it are killed, Gaden said.
Three Minnesota DNR workers are among those trying to control the species. In a 25 foot Boston Whaler, they leave the shore of Lake Superior north of Duluth and head toward a 750-foot-long net they set deep in the water the day before. Every spring the DNR catches lake trout along the North Shore to count how many fish are suffering lamprey wounds.
The annual surveys indicate the lamprey control program is working, said Goldsworthy’s boss, DNR area fisheries supervisor Don Schreiner.
Every year the U.S. and Canadian governments spend about $20 million dollars on the lamprey control program. But the success story has a sober ending. The sea lamprey is the only species out of about 180 exotics to invade the Great Lakes that can even be controlled. Scientists say there’s no hope it will ever be completely eradicated.