The Lake Mille Lacs walleye population has declined to the second-lowest level since monitoring began in 1983.

And Department of Natural Resources officials aren’t sure why.

Based on recent netting assessments, the lake’s walleye index dropped from 10.8 fish per net (22.9 pounds per net) in 2010 to 9.7 fish per net (16 pounds per net) in 2011.

The long-term trend of walleye population assessments on Mille Lacs since the mid-1980s has been declining overall, but the trend for female walleyes has been stable. The DNR says this may reflect the fact that the walleye harvest strategies employed by both the state and the Chippewa Bands, are more selective for smaller, male walleyes.

The implications of the decline in males to the overall fishery are not clear, the DNR says. And it’s unclear whether the new information will affect fishing regulations on the lake, the state’s most popular walleye fishery.

DNR managers will meet with the Mille Lacs Fisheries Input Group, an advisory group of anglers and local business interests, to discuss the status of the lake’s fish populations before setting 2012 regulations.

The DNR says walleye fishing has been good at Mille Lacs, and fisheries managers believe good fishing may continue this winter and spring, even in the face of a decreasing walleye population. This may be due to relatively low numbers of young-of-the-year perch, the primary food sources for young walleye. The perch are also small, according to the new assessment data.

Fisheries managers say a smaller perch population typically results in hungry walleyes. Looking to 2012, a resulting high harvest would be a concern if it is projected to reach or exceed the state’s allocation, which will be set in February in cooperation with Chippewa Band managers.

Meanwhile, northern abundance also went down — expected given a regulation change in 2011. The former regulation was a 24- to 36-inch protected slot that allowed the keeping of one northern longer than 36 inches. In 2011, a new regulation protected northern from 27- to 40-inches and allowed the taking of one fish longer than 40 inches.

Tullibee (cisco) abundance also dropped in 2011 from relatively high abundance levels in 2009 (34 fish per net) and 2010 (11 fish per net) to catches of less than two per net in 2011. The relatively warm late summer may have resulted in higher mortality for this cold-water species.

Smallmouth bass have been increasing in abundance for many years, and although not at an all-time high as observed in 2009 (1.9 fish per net), they were above average in abundance at 1.1 fish per net.