Mille Lacs Treaty Management Fact Sheet
Since treaty management began, the DNR has used restrictive regulations to keep the total walleye harvest (including tribal harvest) an average of 200,000 pounds lower than in the 10-year pre-treaty period, when the angler catch (including hooking loss) averaged more than 590,000 pounds.
The DNR calculates the safe harvest level based on its estimate of the number of walleyes in the lake. That estimate comes from a computer model that relies heavily on data that is guesstimated, simulated, assumed or generated randomly.
Gillnetting results are an important factor in the computer model, but the gillnets do not provide a representative sample of the walleye population because they are set near shore. There are some new sets farther offshore that have higher catch rates but the model gives them little weight. There is no netting in the mid-lake region.
The harvest cuts were made despite the fact that the walleye population has remained healthy, with no significant changes in any of the indicators biologists normally monitor. Since the mid-70s, for example, the gillnet data shows slight increases in pounds of walleye per net and average weight of walleyes in the catch, and a slight decline in number of walleyes per net. But the latter is most likely a result of the tight slot limits.
Important creel statistics like catch per man-hour and average walleye weight have shown long-term increases-more evidence that the walleye population is in good shape.
The DNR calculates an exploitation rate to show what percentage of catchable size walleyes are being harvested each year. According to the treaty-management agreement, the rate cannot exceed 24%. The rate averaged 23% in the pre-treaty
period, but only 15% since treaty management began.
Tight harvest slots have resulted in a depletion of mid-size walleyes and a build-up of bigger and smaller ones. The gillnet catch of walleyes in the 16- to 18-inch slot was down by about 50% in 2001 while the catch of 20- to 24-inchers was up by about 50%.
The new 2002 slot will target walleyes in the 14- to 16-inch range, a size class that was already down 36% in the 2001 gillnet survey.
The tight slots resulted in a hooking loss estimated to be more than 79,000 pounds in 2001, nearly twice the average tribal harvest. But the DNR has no data on the true hooking mortality rate, which could easily be twice the rate being used.
The build-up of big walleyes, along with good numbers of large pike and muskies, may be decimating forage crops. In 2001 sampling, practically every kind of baitfish was down at least 87 percent from pre-treaty levels and some, like trout perch and young-of-the-year suckers and tullibees, were not found at all.
Because of the food shortage, large walleyes are growing more slowly and are skinnier for their length. The weight of a typical 9-year old walleye, for example, decreased by 25 percent from 1999 to 2001.