KALISPELL - Montana's bull trout are not faring overly well in the Swan River drainage, where introduced lake trout appear to be outcompeting - and eating - the natives.

Biologists, who spent much of October counting fish nests, predict that if lake trout continue to prosper, anglers should expect substantial changes to the species mix in Swan Lake.

For nearly 30 years, scientists have gone to the Swan to count "redds" - the underwater nests where bull trout lay their eggs. The high mark of 612 redds came, ironically, in 1998, which was the year bull trout were granted protections under the federal Endangered Species Act.

At the time, the Swan was considered a stronghold, as native fish elsewhere in the Flathead River system were struggling.

Now, that situation has reversed.

While the Flathead system is holding steady, this year's Swan drainage redd count - 366 - is the lowest since 1992. Nearly 400 were counted last year, 521 the year before that.

Elk and Squeezer creeks fared worst, registering redd numbers well below the recent average. In fact, redd counts in Elk Creek have not been this low - 134 - in almost a quarter-century.

State fisheries biologist Tom Weaver said teams have been monitoring Swan Lake populations carefully, aware that invasive lake trout have been reproducing there for years. He warns continued declines of bull trout are likely there if the non-natives spread further.

Predatory, non-native lake trout, in fact, are considered - alongside drought and habitat degredation - a primary factor in bull trout demise. They were first introduced to Flathead Lake in the early 1900s, part of an attempt to produce a commercial fishery strong enough to encourage settlement in the area.

Today, the region is surely settled, the lake trout are thriving and the natives are, in some waters, nearly gone.

A prime example can be found in Bowman Lake, located upstream from Flathead Lake in Glacier National Park's western fringe. In 1962, an angler hooked the first lake trout known there. In 1969, scientists fishing with gill nets could still snag about five bull trout per net, and no lake trout.

But when they repeated the gill-net survey in 2000, they hauled in about three lake trout per net, and almost no bull trout. They recorded full a full reversal in species mix in just 30 years.

The past 30 years have been busy with monitoring, as biologists take to the field each fall for the annual redd count. This year's work showed below-average counts in both the Swan and the South Fork Flathead River drainage.

The South Fork total - 66 redds - was down from 74 last year, 161 the year before that, and 174 the year before that.

The numbers, however, may not accurately reflect general population trends. Bull trout remain for a few years in the small streams where they are born, before migrating down into larger lakes such as Flathead and Swan. They return to their birth streams at about age 6 or 7 to spawn the next generation.

That means this year's redd count actually represents an echo from 2003 - when the South Fork produced a paltry 76 redds - rather than a precipitous decline from the past few years.

The same delayed biological schedule may help explain numbers from the North Fork Flathead River drainage, which came in at 85 this year (down from 106 last fall, 122 in 2006, and 144 in 2006). The drop may echo the slim redd year of 2003, when only 61 egg nests were counted.

Still, the North Fork - unlike the South Fork and the Swan - registered near the 10-year average, far higher than the low of 44 in 1997 and far shy of the 1982 high of 406.

Likewise, counts in the Middle Fork Flathead River drainage came within the 10-year average, at 102 this year. (The high there was 173 in 1985, and the low of 31 came in 1996).

While the river system upstream of Flathead Lake seems to be stabilizing after the 1990s crash, biologists now are turning their attentions to the Swan drainage. The most recent monitoring there comes on the heels of more bad news from the Swan - in June, netting turned up the first invaders in Lindbergh Lake, four lake trout ranging from 16 to 19 inches long.

Reporter Michael Jamison can be reached at (406) 862-0324 or mjamison@missoulian.com.