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Biologists try to determine what's ailing walleye population on Mille Lacs Lake

AITKIN, Minn. -- It's an angling irony. Walleye fishing has been very good on Mille Lacs Lake this summer. Most days, anglers on this treasured Minnesota walleye lake can catch plenty of walleyes, many of them from 20 to 27 inches long.

But the Mille Lacs walleye population is not as healthy as it might appear.

Last fall's walleye net catches by Department of Natural Resources crews were the lowest in 40 years. While anglers are catching lots of larger walleyes, they're having trouble catching smaller ones, including the 18- to 20-inchers legal to keep for a meal. Only about one in eight walleyes that anglers catch is in that size range, according to angler surveys, said Eric Jensen, DNR large-lake specialist at Aitkin.

Even the larger walleyes are skinny, well below the weights they might have been in past years, due to a shortage of forage fish in the lake.

After seeing last fall's dire netting results, the DNR tightened walleye regulations on Mille Lacs this year, allowing anglers to keep just two walleyes from 18 to 20 inches long, or one in that size range and one over 28 inches long. Last year, regulations allowed Mille Lacs walleye anglers to keep four walleyes under 17 inches long, with the exception that one could be longer than 28 inches.

Of further concern to anglers and fisheries biologists, walleye year classes from 2009 to 2012 have failed to contribute significantly to the lake's walleye population, and small walleyes have begun to show up in stomach samples taken from northern pike, smallmouth bass and larger walleyes.

The DNR also changed bass regulations on Mille Lacs this year. For the past several years, anglers could keep just one smallmouth bass on Mille Lacs, and it had to be longer than 21 inches. This year, the limit was changed to six, with a protected slot limit from 17 to 20 inches, except that one can be longer than 20 inches.

The bass population has expanded about 20-fold since the mid-1990s, Jensen said, but growth rates have slowed in recent years. Fisheries managers believe that harvesting more bass might help increase growth rates again.

Managing harvest

As a result of federal court decisions in the 1990s involving American Indian treaty rights, both the DNR and eight bands of Minnesota and Wisconsin Chippewa must harvest walleyes on Mille Lacs under a "safe harvest" framework. The DNR and the Chippewa each manage their own fisheries, and the two meet annually to agree on safe harvest levels.

As a result of concerns over the walleye population, the two parties agreed this year to cut in half the total allowable harvest for sport angling and Chippewa netting, from 500,000 pounds last year to 250,000 pounds this year.

Of this year's total allowable harvest, sport anglers are permitted 178,750 pounds of walleyes and the Chippewa are permitted 71,250 pounds, Jensen said. This past spring, during the walleye spawning period, Chippewa netters and spearers reported taking about 15,000 pounds of walleyes, DNR officials said.

Through June 30, sport anglers had harvested about 71,000 pounds of walleyes, Jensen said. That figure includes estimated hooking mortality, or fish that die after being released. Also through June 30, anglers had released an estimated 800,000 pounds of walleyes, Jensen said, compared to about 1.4 million pounds released during the same period last year.

What's wrong?

DNR fisheries officials say they're uncertain what is causing the decline in the lake's walleye population. Their fundamental concern is that not enough small walleyes are becoming big walleyes because of increased mortality rates.

"Our reproduction is good," Jensen said. "But the strange thing that's happening is, once we get past that age-zero, our survival of small fish really goes down."

With the lake's perch population down by about half, larger fish, including walleyes, must turn to some other fish for forage, Jensen said.

"What that suggests to me is that in the absence of normal forage, the walleyes and other predators are eating what's most abundant, which is young-of-the year walleye," Jensen said.

Stomach content analysis of larger walleyes and other predator fish has indicated that's exactly what's happening, he said. More stomach content analysis is planned, DNR officials say.

The lake also is changing as a result of aquatic invasive species, Jensen said. Zebra mussels were discovered there in 2005, and their numbers grew exponentially until last year, he said. They filter algae, an important part of the food chain. The lake has become much clearer in recent years, a common occurrence where zebra mussels become established.

"We have quite a bit of uncertainty about the role aquatic invasive species are playing," Jensen said. "That's the big monkey wrench thrown in the middle of this."

Netting an issue

Many nonband residents in the Mille Lacs area contend that Chippewa netting of spawning walleyes is the main cause of the lake's declining walleye population. Longtime Mille Lacs resident and fishing guide Steve Fellegy in March created an organization called Save Mille Lacs Sportfishing aimed at forcing the DNR back to court to get netting stopped.

"I can't see another route out of this," he said. "We're not fighting treaty rights. We're forcing the DNR to go back to the court and say, 'This is wrecking the lake.' "

He also supports a moratorium on sport fishing.

"Sport angling and netting, any kind of harvest, should be stopped for a period of years like they did on Red Lake," Fellegy said.

The DNR's Tom Jones, regional treaty coordinator at Aitkin, says the lake's walleye problems are more complex than simply netting.

"People believe that Indian nets are causing all the problems," Jones said. "But if you look at the relative take (of walleyes) by anglers and netters, anglers are still taking more little fish and more total fish. It's probably the case that the combined band and state fisheries influence the walleye population. It's not as simple as saying one side caused it and one didn't."