- Associated Press - Saturday, May 16, 2015

ATWATER, Minn. (AP) - One day, Diamond Lake walleye from Central Minnesota might populate southern Minnesota lakes with a strain more suited for those shallow, nutrient-rich waters. Researchers discovered the genetically unique population while unraveling the mystery of Lake Sarah.

On this day in mid-April, however, Diamond Lake wasn’t giving up much in the way of potential brood stock. Two nets had blown down and a third had tangled in 40 mph winds the day before.

Spicer area fisheries supervisor Dave Coahran and Assistant Supervisor Brad Carlson worked the northwest corner of the lake, pulling up each of the 11 nets that extended about 40 feet perpendicular to the shore. They worked out the snarls, retied the openings, reset the nets on the cobbled lake bottom. By Net four, the first walleyes turned up. Coahran and Carlson ran a thumb along the belly of each.

“She’s partially spent,” Coahran said, tossing a female back into the water. Green females, those that aren’t yet releasing eggs, went back, too.

Ripe females went into one side of a divided, aerated tank; males into the other. Spicer is the only one of the Minnesota Department of Natural Resources’ eight egg-take stations that harvests walleye eggs from more than one lake, the St. Cloud Times (https://on.sctimes.com/1IxllY2 ) reported.

The Spicer quota, 180 quarts, would come from four lakes - Diamond, Rice, Koronis and Elizabeth. The resulting walleye fry, fish about the size of a mosquito, will stock some of the 39 lakes managed by Spicer staff. Spicer also sends fry to Windom, whose territory includes Lake Sarah.

By late morning, Coahran and Carlson had transferred 21 Diamond Lake females and 15 males from boat to DNR truck and headed for the New London hatchery.

The effort produced only 1 quart of the pure Diamond Lake strain. Fertilization is more successful when the eggs of four females mix with the milt of 10 or 11 males.

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Crews obtained eggs from Diamond Lake walleyes for the first time two years ago. DNR fisheries research scientist Loren Miller called the timing fortuitous. He had been tracing the genetics of Lake Sarah walleye, which didn’t match northern populations.

“The question was where were they coming from if not the introduced northern stock,” Miller said.

Lake Sarah sits in Murray County, part of the 10-county Windom area where walleye reproduce naturally in only about 10 percent of the 100 managed lakes. The eggs tend to smother under layers of sediment. The 10- to 11-foot-deep lakes tend to winter kill.

“Walleye is the king of Minnesota, so a lot of walleye management does occur,” said Ryan Doorenbos, Windom area fisheries supervisor.

Back in 1991, Windom area fisheries staff was seeing walleye of an age that couldn’t be attributed to stocking. Lake Sarah hadn’t been stocked for eight years. The walleye population was not only naturally reproducing, it was increasing. In 2001, the office got $500 from a Worthington fishing club to sample 50 walleyes. Turned out they were different from the fish stocked in surrounding lakes.

“This prompted us to say, ‘Does this strain have a unique predisposition to spawn on southern lakes?’” Doorenbos said.

Researchers knew Lake Sarah had been stocked with Cannon River sources in the 1970s. Attempts to explain Lake Sarah also led Miller to test Spicer-area lakes, which produce a unique strain derived from the Crow River.

“At least Rice, Koronis and Diamond lakes all still maintain a distinct strain, even though fish from other places have been stocked on top of them in the past,” Miller said.

That tells him stocked fish that haven’t adapted to the conditions aren’t crossing with the fish that originate from local sources.

“They’re looking at whether we can develop another brood stock based on these fish and see if we can enhance natural reproduction on some other southern Minnesota lakes since that strain seems to perform better,” Miller said.

Success could make a small dent in the bigger picture.

The DNR stocks about 1,050 of Minnesota’s 11,842 lakes, an effort that costs about $3.5 million a year and puts 350 million to 450 million walleye fry into lakes.

Next year, Doorenbos said the Windom staff plan to stock walleye traced to the Cannon River source in four lakes where they’re more likely to reproduce naturally. How the fish take hold won’t be known until they spawn in five or six years.

“Our goal is to create a self-sustaining population in those four lakes,” Doorenbos said.

Eventually, the Diamond Lake strain could be stocked in southern lakes. This year, for the first time, the DNR harvested walleye eggs from Lake Sarah.

For now, the Spicer crew will repopulate lakes within its area with the Diamond Lake strain. Ten percent of the egg take will return to Diamond Lake in the form of walleye fry.

By the end of their four-day walleye run, Spicer crews would take 63.25 quarts from Diamond Lake. The season’s take from all four lakes totaled 231.5 quarts.

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Back in New London, the truck pulled into the hatchery, where a shed covers the raceway.

Clad head to toe in rain gear, workers netted the walleye out of the truck’s holding tanks. The females went into a blue barrel of water treated with a chemical to temporarily slow their breathing. Reducing the fight makes stripping easier on both fish and people.

Once the females turn belly up, they’re scooped out of the water, blotted dry on a towel cinched taut over another barrel, stripped of lemon-yellow eggs and tossed into the water-filled raceway. Then the males are stripped of milt.

Once 48-degree refrigerated river water is added to the plastic tub, fertilization takes place within about two minutes. The mix is gently stirred with a goose feather. A gray clay slurry, which reduces clumping, is added and stirred for another minute before the tub is emptied into a floating crib.

The name of the origin lake is written in black marker on the white tubs, and tagged to the wooden crib covers. Eggs are gently rocked in the cribs and then left overnight to harden.

Fish are returned to the lake.

Hardened eggs are taken to the hatchery.

By now, they’re sturdy enough that Gary May, natural resources specialist, can use a wooden ruler to level them off as he measures out three 1-quart saucepans per numbered plastic container.

May connects the containers to the water supply, and adjusts the flow until the yellow eggs roil gently from the bottom.

Once they hatch, fry will be piped into holding tanks.

Besides eggs collected locally, New London was scheduled to hatch another 120 quarts collected from Pine River and 120 more from private sources. All told, New London received 491.5 quarts of walleye eggs this season.

Minnesota’s 11 hatcheries were slated to receive nearly 4,200 quarts of walleye eggs. Depending upon the source, each quart contains 120,000 to 137,000 eggs.

Hatchery staff can measure the initial stage of success in about 18 days, when the fry emerge. The average hatch rate is 65 percent.

Despite the careful observation, timing, measuring and follow-up lake sampling, the fish retain a few secrets - such as precisely why some strains remained pure.

“What my work does can’t tell me why, it’s just providing evidence that it is happening,” Miller said.

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Information from: St. Cloud Times, https://www.sctimes.com


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