Walleye numbers in Lake Mille Lacs -- the state's most popular walleye fishery -- have fallen to their lowest level in 40 years, and officials aren't sure why.
The lake's larger walleyes also are skinny, a sign they are not finding enough food.
"We're concerned,'' said Department of Natural Resources fisheries research manager Don Pereira. Causes could be as varied as the harvest regulations governing sport anglers and Chippewa netters, the explosion of zebra mussels in the lake, improved water clarity or the amount of prey fish such as perch and tullibees.
It's too early to say if the DNR might tighten walleye regulations on the huge lake, Pereira said. Further restrictions could undercut the tourist industry, business owners say. Anglers this summer could keep walleyes less than 17 inches and could keep one fish over 28 inches.
DNR survey nets this fall averaged 4.8 walleyes -- the lowest since 1972 and a continuation of a decline that began in 2009. Last year, 9.7 walleyes per net were recorded.
The disappointing results further complicate the lake's walleye management. DNR officials already were worried about declining numbers of male walleyes, the focus of a meeting next week between DNR and tribal fisheries researchers.
"This raises the urgency'' of those discussions, Pereira said.
The balance between regulations and attracting anglers is fragile, business owners around the lake say.
"If anglers can only keep a couple of fish, they'll go someplace else,'' said Eddy Lyback, who owns Mille Lacs marine and ice fishing businesses.
"This should give the state more leverage to stop the springtime gill netting (by tribes).''
Ironically, said Terry McQuoid of McQuoid's Inn, sport fishing was excellent this summer.
"This was a fantastic year,'' he said. But 70 to 80 percent of the catch was within the protected slot and had to be released, he said.
The hot bite might have been the result of too few forage fish in the lake.
"Fishing success is driven as much or more by forage abundance as abundance of fish themselves,'' Pereira said.
Of factors affecting the Mille Lacs fishery in recent years, the exponential growth of zebra mussels is perhaps least understood and could have affected the net survey's accuracy.
"I think the zebra mussels could play a role in the test net results,'' said former DNR fisheries biologist Dick Sternberg. "But there are so many factors affecting Mille Lacs walleyes now, with slot limits and netting and perch abundance, it's confounding.''
The poor condition of larger walleyes caught in the DNR nets could be tied to a lack of juvenile tullibees, said Rick Bruesewitz, DNR area fisheries supervisor.
Walleyes also feed on perch, and their numbers were also down in the survey.
"We had a heck of a tullibee kill this summer,'' Bruesewitz said. The deaths were caused by water temperatures near 80 degrees.
A DNR walleye-tagging study this spring will offer another estimate of the population and will be compared to the gill net survey. But the results will come too late to help set walleye regulations for the 2013 open-water season.
The DNR will take some good news to its meeting this winter with the Mille Lacs Input Group, a consortium of area resort owners, bait shops and other businesses, to discuss their research and regulation options: Electrofishing surveys showed Mille Lacs walleye reproduction this year appeared to be good.
Sport anglers have harvested about 320,000 pounds of Mille Lacs walleyes so far this year. Combined with the 80,000 pounds netted by the Chippewa bands this spring, the harvest remains below the 500,000 pounds the DNR and tribal officials set for 2012.
A 1999 U.S. Supreme Court decision affirmed off-reservation hunting and fishing rights held by the eight Chippewa bands and established the "co-management'' of Mille Lacs between the state and the bands.
Failing agreement with the bands over possible management changes, the DNR can act unilaterally, but only under certain conditions, such as conservation of the resource.
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walleyes per DNR survey gill net, down from 9.7 last year.