Biologists keep an eye on walleyes

(Bob King/Duluth News-Tribune/MCT)
Dennis Pratt, a volunteer with the Wisconsin DNR, empties a hefty walleye...
Story by Sam Cook
Duluth News Tribune
April 16, 2012
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DULUTH, Minn. — The tail of the huge mama walleye broke the surface of the water, flexing slowly, side to side. It was a massive tail, as wide as a handspan. Soon it would be fanning the tannin-stained water of the St. Louis River over a patch of gravel as she deposited her payload of eggs.

But not today.

One Thursday morning, the big girl had been detained for a few minutes by fisheries biologists with the Minnesota and Wisconsin Departments of Natural Resources. Nine biologists, both current and volunteers coming out of retirement, were doing their annual spring walleye sampling.

For at least 30 years, the two agencies have combined forces to gather information on the walleyes both states share in the St. Louis River estuary.

“The goal is to index the spawning population of western Lake Superior and the St. Louis River,” said John Lindgren, fisheries specialist senior with the Minnesota DNR. “We want to monitor catch rates and size and age structure of these fish.”

The data comes in handy when anglers ask Lindgren or other biologists what’s happening with walleyes in this popular fishery.

Paul Piszczek, the new Wisconsin DNR fisheries biologist in Superior (replacing Dennis Pratt), lifted the big walleye from the tank on board a DNR johnboat and laid her gently on a measuring board.

“761,” Piszczek called out.

That was her length in millimeters. She was a 30-inch walleye, and her scaled flanks gleamed green and gold in the early-morning light. She was the kind of walleye every walleye angler dreams of catching, and she would never look better than at this moment. Her jaws were huge, her eyes the size of quarters, her body bulging with thousands of eggs.

What a gorgeous creature.

The assembled biologists took the second spine of her dorsal fin, whose annual rings would later reveal her age. Dan Wilfond, a Minnesota DNR fisheries specialist, recorded her length and gender on his laptop computer.

The big female was one of 41 walleyes in the tank. They had been captured upriver, near the generating station below the Fond du Lac Dam. The walleye spawning run usually would peak between April 18 and 22, when water temperatures reach 48 degrees, said Bill Blust, Wisconsin DNR fisheries specialist in Superior. But with the unseasonably warm and advanced spring, biologists decided to start.

Earlier that morning, Lindgren and a crew of three had taken the DNR’s electro-shocking boat upriver. A boom with electrodes dangling in the water off the bow put a mild current in the water. Momentarily stunned walleyes flopped to the surface, where Pratt and Peter Stevens, Lake Superior fisheries manager for the Wisconsin DNR, netted the fish and dropped them in a tank of water amidships.

The netters had to be quick. When Pratt and Stevens saw a fish flopping to the surface, they stabbed the water with their dipnets, rarely missing their targets.

Once the tank was filled with fish, Lindgren and his crew motored to another DNR boat tied off in a narrow channel off the main river. That’s where the processing crew worked.

The agencies try to work up 1,000 fish each spring, figuring that’s a sample size that will give them accurate information. The data they get will tell them what proportion of the walleye population is made up of each length of fish. That is how the agencies know when a bumper year-class of walleyes is moving through the population.

“We’ve got a big year-class coming in now, we think,” Blust said. “Four-year-olds. Thirteen to 15 inches long. That’s a good thing. We need that big year class. The big year classes drive the fishing.”

This particular Thursday was going to be a slow day for electro-fishing, Blust said, watching Lindgren’s crew make its first downstream pass.

“They should really be getting them here,” he said. “It’s really slow.”

The water temperature was 46 degrees, Lindgren said. That’s not quite prime time for walleye spawning, but with the early and unseasonably warm spring, the agencies didn’t want to take a chance on missing the run.

There would be more productive days this spring.

“You can’t rush mother nature,” someone said.

Piszczek lifted the hog walleye from the measuring board, cradling her underside with one hand, holding just in front of the tail with his other hand. Without delay, he swung her over the side of the boat and slid her into the water.

One flap of her tail, and she was gone. Off to make more baby walleyes for anglers to catch in 2017 and beyond.

Sam Cook

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