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Sea lamprey numbers up in Lake Superior

The population of fish-killing sea lamprey is going up in Lake Superior and is now more than double the target level set by the Great Lakes Fishery Commission. Photo courtesy of Minnesota Sea Grant.

The population of blood-sucking, fish-killing sea lamprey in Lake Superior is going up, the Great Lakes Fishery Commission reported Thursday.

The commission said lamprey numbers are down in lakes Michigan, Huron and Ontario but up in Erie as well as Superior. And they aren't sure why the Lake Superior lamprey population is more than double the target level.

"They had been on a downward trend for about eight years until this tick up," Marc Gaden, Great Lakes Fishery Commission spokesman, told the News Tribune.

If the commission can't get the lamprey increase under control it could be bad news for Lake Superior anglers. There are now an estimated 100,000 adult lamprey in the lake, well above the goal of 45,000, Gaden reported, but well below the 800,000 level at their peak 60 years ago.

"We're above goal, and it is a concern that it went up, but it's still just a fraction of what it was before treatment started in the 1950s," Gaden noted.

Lamprey swam their way out of the Atlantic Ocean and into Great Lakes infamy a century ago through man-made canals and remain a major predator of fish such as lake trout. The Great Lakes Fishery Commission is in charge of the constant battle to poison enough lamprey to allow Great Lakes fish to survive — a more than $21 million annual effort to preserve the $7 billion annual Great Lakes fishing economy.

Lamprey populations across the Lake Superior region may be rebounding after the harsh winters of 2013 and 2014, Gaden said, and could be responding to both increased fish populations and generally warmer water temperatures, which lamprey like.

"We're looking at whether climate change is going to make more streams more suitable for lamprey," he said.

Lamprey are targeted as juveniles in the rivers where they spawn, with a focused toxic chemical that kills them in the stream without killing native species. Many Lake Superior tributaries are treated on a revolving basis. But it appears lamprey are now spawning in more rivers.

The Commission is looking at the Chippewa, Nipigon, Gravel, and Batchawana rivers as sources of additional lamprey for Lake Superior.

Ironically, as rivers are cleaned up and fish habitat restored, they may become more suitable for lamprey to spawn. The lampricide chemical also doesn't work well in large rivers.

"The Bad River has also been treated recently, however, some concerns remain that treatment effectiveness may not have been ideal for this system," the commission reported Thursday.

"We haven't yet found them in the St. Louis itself, which is good news. But there's no reason they shouldn't be spawning there, so it is a concern going forward," Gaden said, due to the improving water quality and restored fish habitat in the river. "Lamprey are a fish, so conditions are getting better for them in the St. Louis, too."

Lamprey nearly wiped out all Great Lakes fish by the mid 20th century but the annual chemical attack has kept them in check. Before control, sea lampreys killed an estimated 103 million pounds of fish per year. Now, because of control, sea lampreys kill less than 10 million pounds of fish per year.

To stem the increasing lamprey tide on Lake Superior, Gaden said crews may decide to treat new rivers or treat known lamprey hotspots more often. The Minnesota Department of Natural Resources in June reported that lamprey have been spawning in the lower Knife River on the North Shore in recent years, the first time that's ever been seen.

"We're checking to see if there are new sources, new rivers where we didn't know they were coming from," he said.

While zebra mussels, goby and the potential invasion of Asian carp get more headlines as destructive invaders, nothing has compared to sea lamprey for sheer devastation of Great Lakes fish.

The commission calls the sea lamprey "one of the worst human-caused ecological disasters ever inflicted upon the Great Lakes." They attach to fish with a tooth-filled, suction cup mouth and file a hole through the fish's scales and skin with a razor-sharp tongue. The average sea lamprey will kill up to 40 pounds of fish during its adult, parasitic stage. Sea lampreys prefer trout, salmon, whitefish and sturgeon but they also attack smaller fish such as walleye and perch.

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