Biologists implant acoustic transmitters in St. Louis River sturgeon to monitor their movements
The surgical patient lay on the operating table, belly up, on Monday afternoon. A cool breeze drifted up the St. Louis River. Canada geese honked overhead.
As operating rooms go, this one had a pleasant atmosphere.
The surgeon, Anna Varian, held a scalpel in her right hand, ready to make her initial incision.
"They have really tough skin," Varian said.
She was talking about the adult lake sturgeon that lay before her upside down, gills flexing, mostly submerged in river water.
Varian, assistant Duluth area fisheries supervisor for the Minnesota Department of Natural Resources, began slicing through the sturgeon's white belly. The unsedated fish, perhaps 45 inches long, did not flinch.
The sturgeon had been captured earlier just upstream by a DNR crew using an electro-fishing boat. In electro-fishing, a generator on the boat sends electrical current into the water, momentarily stunning nearby fish. When a sturgeon comes flopping to the surface, biologists on board net it.
Varian's plan was to implant in the sturgeon's underside a hydro-acoustic tag, or transmitter, that will help fisheries officials track movements of the fish. The sturgeon-tagging project was launched this spring. Fisheries biologists hope to put acoustic tags in about 60 St. Louis River sturgeon in the Twin Ports to monitor their movements, said Pat Schmalz, DNR fish research supervisor at French River.
The acoustic tagging project 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.
With Wisconsin DNR fisheries technician Aaron Nelson holding Varian's sturgeon patient in place, she made a slit about 1½ inches long in the fish's skin. She placed the acoustic tag — about the size of tube of lipstick — into the slit and made sure it lay flat inside the sturgeon.
Still the fish did not budge.
Varian then went to work closing the incision with a few stitches, a skill she said she perfected by watching YouTube videos. Once she was finished, the fish was taken to recovery — an oxygenated tank of water near shore. When it had fully recovered, it was set free in the river and swam off as if nothing had happened.
Receivers in place
Already, fisheries workers have placed four acoustic receivers at key spots in the river, with nine planned in all. Whenever a tagged fish passes within 400 to 600 meters of one of the receivers, it will pick up the fish's signal, Schmalz said. Receivers placed in both the Duluth ship canal and Superior Entry will document passage of sturgeon in and out of the lake.
"We can learn a little bit more about their movement, and track them, see when they come in and out of the river and what habitats they're using," Varian said.
Sturgeon spawn this time of year just below the Fond du Lac Dam on the river. Some live in the river much of the year, while others migrate down to Lake Superior and disperse along the South Shore as far away as Chequamegon Bay, Schmalz said.
Although anglers have been inadvertently catching and releasing St. Louis River sturgeon for many years, last year it became legal to target the species. All sturgeon caught by anglers on the river must be released. Anglers have taken sturgeon up to at least 60 inches, and the DNR captured one on Wednesday that was 65 inches long, the longest that biologists have seen on the river.
Another sturgeon success
The success of St. Louis River sturgeon follows that of the Rainy River on the Minnesota-Ontario border, where sturgeon have flourished after commercial fishing ended on Lake of the Woods. There, the DNR has captured sturgeon up to 78 inches long, and reliable angling reports tell of sturgeon up to 84 inches long, said Phil Talmage, DNR area fisheries supervisor at Baudette.
"If we had something like that here, that would be great," Schmalz said. "Now that we have things like the catch-and-release season opening, we think we need to know more details about the population of sturgeon so we can manage it."
The sturgeon recovery is one of the St. Louis River's most notable success stories since cleanup efforts began in the late 1970s. In the years prior, the species was essentially extirpated by overfishing and by pollution in the river. First stocked by Minnesota and Wisconsin DNRs in 1983, sturgeon have re-established themselves and are now spawning in the river. Evidence of their spawning — tiny sturgeon fry and other juvenile sturgeon — have been discovered in the river in recent years. Sturgeon stocking ended on the river in 2000.
Other fisheries agencies around Lake Superior also are doing acoustic monitoring of sturgeon, Schmalz 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, Schmalz said. Each agency's transmitters and receivers will monitor the passage of sturgeon from any other jurisdiction, he said.
The Minnesota DNR also has used acoustic tagging on other species in the state, including walleyes, muskies, northern pike and invasive carp.