DULUTH - St. Louis River muskie anglers learned something fascinating this past week about the fish they chase all summer: Not all of them stay in the river.
Of 60 muskies that have been fitted with hydro-acoustic "tags" by researchers, nearly 40 percent have ventured into Lake Superior, and 25 percent have remained there for more than a month. One of them swam all the way to Chequamegon Bay near Washburn and another to Bark Bay of Lake Superior near Cornucopia.
"We were extremely surprised that so many fish went out to the lake and spent so much time there," said Curt Ellestad, president of the Lake Superior chapter of Muskies Inc.
It opens new possibilities to local muskie anglers, he said.
"You can go out in Lake Superior and fish them," Ellestad said. "It makes sense to me."
Researchers, too, were somewhat surprised.
"I expected them to use Lake Superior, but the rate they're going out there is higher than I expected," said Jeramy Pinkerton, a fisheries specialist at the Minnesota Department of Natural Resources. "The fact that we had one that went to Chequamegon Bay - I don't think a whole lot of people expected that."
"It's certainly an eye-opener," said Paul Piszczek, Wisconsin Department of Natural Resources fisheries biologist in Superior.
Last year was the first year of a five-year acoustic monitoring study of the river's muskies.
The project is a cooperative effort of the Minnesota and Wisconsin DNRs and the University of Minnesota. It's funded by Minnesota Sea Grant.
Several members of the Lake Superior chapter of Muskies Inc. helped with the project last summer, when the muskies were captured and fitted with the hydro-acoustic transmitters. That was done surgically, by cutting a small slit in the underbelly of each fish and slipping in a transmitter about the size of a tube of lipstick.
Erin Schaeffer, a University of Minnesota graduate student, did nearly all of those surgeries. She, too, was surprised so many of the river's muskies moved into Lake Superior at times.
"I don't know if we'll ever know why they went that far," Schaeffer said. "The lake is so cold. I have no idea why they'd leave a river system that seems to offer everything they need."
The muskies' movements were recorded on receivers that picked up signals transmitted from the fish. Forty receivers are spread out through the estuary, as well as in the Duluth ship canal, Superior Entry and in Lake Superior. (The signals picked up at Chequamegon Bay and Bark Bay were recorded on receivers placed by the U.S. Fish and Wildlife Service, which is monitoring sturgeon movements.)
At a Muskies Inc. meeting Tuesday, March 13, in Duluth, Schaeffer showed maps of the muskies' movements in the St. Louis River and Lake Superior. Red shading on the maps showed where most muskies were spending time from spring to summer to fall. As an angler, Ellestad was amazed.
"This is a game-changer," Ellestad said. "It's unbelievable, because it tells us where we should be spending our efforts. It's a revelation."
The first year's research showed that many muskies spent the spring season generally in the Spirit Lake and Pokegama Bay area, summers spread from Spirit Lake to Pokegama Bay to the Duluth-Superior harbor, and the fall season from Pokegama Bay to the lower river and into nearshore areas of Lake Superior.
Difference between strains?
Researchers want to better understand the movement patterns and habitat use of muskies, and to determine if there's a difference in habits among the Minnesota strain of muskies, the Wisconsin strain and a hybrid of the two, Pinkerton said. They've documented that already.
"One big thing we're seeing is that the Leech Lake strain (stocked by Minnesota) seems to be using Lake Superior a lot more than the Wisconsin strain or the hybrid strain," Pinkerton said.
Thirteen of the 15 muskies that spent a month or more in Lake Superior were of the Leech Lake strain, he said.
That kind of information could have implications for future stocking efforts, Pinkerton said. Anglers tend to prefer larger muskies, and the Leech Lake strain grows larger than the Wisconsin strain, he said. But it would seem that a portion of those Leech Lake strain fish might be less available to anglers if the fish are in Lake Superior part of the year.
More to learn
Researchers aren't sure why the muskies leave the river for Lake Superior. It's unlikely for food, Pinkerton said, because fish of two strains rarely left the river. It could be that the Minnesota fish, originating from a larger body of water like Leech Lake, are more prone to explore, Pinkerton said.
He cautions that researchers have seen just one summer's worth of data on the muskie movements.
"As we add to this, we could see these trends disappear," he said.
Muskies were first stocked in the St. Louis River estuary in 1983 by the Wisconsin DNR. Both Wisconsin and Minnesota DNRs stocked the species almost annually through 2005. Since then, the agencies have taken a break from annual stocking (except in one year) to see if muskies are successfully reproducing on their own.
This year, researchers will take a closer look at whether muskies are using portions of the river that have been restored through recent Great Lakes Restoration Initiative cleanup efforts, Pinkerton said.
Muskies are considered a self-sustaining population in the St. Louis River, Pinkerton said. Researchers also conducted a population estimate of St. Louis River muskies last year. The population is estimated at 1,704, Pinkerton said.
"We're going to investigate a supplemental stocking program, likely starting in 2019," he said.
The plan would be to stock about 2,500 muskies every other year, he said.