Last spring, on the banks of the St. Louis River, fisheries officials surgically implanted small transmitters in the bellies of 45 lake sturgeon.
Already, the hydro-acoustic tracking project has revealed valuable information to biologists.
“We’re seeing adult-size, mature sturgeon hanging out in the river until mid-summer,” said Anna Varian, assistant Duluth-area fisheries supervisor for the Minnesota Department of Natural Resources. “We didn’t know there was a river population. Now we know there are adult-size fish hanging out all summer long. That will provide a great fishery for people.”
Anglers may fish for sturgeon on the river but must release any sturgeon they catch.
Until now, DNR officials in Minnesota and Wisconsin had thought that perhaps sturgeon were entering the river each spring to spawn, then returning to Lake Superior. The news of a summer-long river population was welcomed by Jason Kahler of Superior, an avid sturgeon angler.
“I think that’s awesome,” Kahler said. “It’s good to know they can survive the river, that it’s not too polluted.”
Like many anglers on the river, Kahler sees smaller sturgeon — up to about 3 feet — jump out of the water occasionally. But he has never seen the big ones jumping.
How tracking works
After implanting hydro-acoustic tags in the sturgeon last spring, DNR crews placed eight acoustic receivers in the river. So far, fisheries employees have brought up four of those receivers to see how many signals they have received from passing sturgeon. If a sturgeon with a transmitter passes within about 400 meters of a receiver, the receiver records a signal from the fish.
The receivers checked by the DNR had recorded signals from 43 of the 45 sturgeon tagged this spring, Varian said. The transmitters issue a signal every 30 to 90 seconds, she said, so it’s possible that the two undetected sturgeon may have passed by the receivers too quickly to leave a signal. Or a tag might have malfunctioned, or the fish may have died.
Varian said fisheries officials are pleased — and relieved — that the transmitters and receivers are working.
“It’s very exciting,” she said. “It’s a little nerve-wracking to push a couple-hundred-thousand-dollar piece of equipment over the side of the boat and hope you find it again. It’s also nerve-wracking to cut into a sturgeon and put a tag into it. To know we’ve had good survival by seeing this data has been a big relief.”
Paul Piszczek, fisheries biologist for the Wisconsin DNR in Superior, said that in the past he has received anecdotal reports of lake sturgeon caught incidentally in the river.
“The acoustic technology provides a more quantifiable view of lake sturgeons’ seasonal habitat use,” Piszczek said, “which can guide habitat management projects throughout the river.”
The four receivers checked had all been placed in narrow areas of the river upstream of the Bong Bridge. Four other receivers are in place near the Duluth ship canal and Superior entry to detect sturgeon movements into or out of Lake Superior, Varian said. Those receivers have not been checked yet.
Each receiver checked so far has had hundreds of thousand of “hits” on it, Varian said.
“It’s an insane amount of data,” she said. “I don’t know how else to explain it.”
Several fish have been tracked at all four of the receivers checked, Varian said, while some fish have been tracked primarily near one receiver.
“One fish has moved about every half-day from one receiver to another,” she said. “They each have their own personality, I suppose.”
The fish tagged this past spring ranged in size from 39 to 65 inches, Varian said.
Determining population size
The research also will help in tracking spawning movements of sturgeon, which biologists need to know in order to better determine the size of the river’s population. Female sturgeon, unlike other species, may spawn just once every three to seven years, Varian said.
“Unlike with other fish, where we can target all of the adult population at one time, we can’t with sturgeon,” Varian said. “It’s important to know how often they’re spawning. By tagging fish and learning something about their movements, we’re hoping to answer some of those questions. That will help with population estimates.”
Other fisheries agencies around Lake Superior also are doing acoustic monitoring of sturgeon in their jurisdictions, DNR officials said. The U.S. Fish and Wildlife Service is doing monitoring near the Bayfield peninsula, and Fisheries and Oceans Canada is doing the same near the St. Marys River near Sault Ste. Marie. Each agency’s receivers will monitor the passage of sturgeon from any other jurisdiction, he said.
The acoustic tagging project on the St. Louis River is a cooperative effort involving the Minnesota and Wisconsin DNRs, the Fond du Lac Band of Lake Superior Chippewa, the U.S. Fish and Wildlife Service, the Nature Conservancy and the University of Wisconsin-Stevens Point.