Bull trout counts variable under difficult survey conditions

FWP field crews have completed the 2005 bull trout redd (nest) counts in monitoring tributaries in the North, Middle, and South Fork of the Flathead drainages, and in the Swan drainage. The annual index sections for all three major populations (Flathead, Swan, and Hungry Horse Reservoir) were surveyed this year, but conditions during many surveys were poor, due to drought during the migration period followed by high flows after extensive rainfall. Compared to last year, counts were up slightly in the combined North and Middle forks of the Flathead, and down in the South Fork of the Flathead and Swan.

According to FWP Fisheries Biologist Tom Weaver, the 2005 numbers should be considered absolute minimum counts because of these difficult survey conditions. Weaver said that it is quite likely that biologists were unable to see an undetermined number of redds.

Flathead Lake Population: This was the 26th year of index counts for the Flathead Lake bull trout population. These fish spawn in tributaries to the North and Middle forks of the Flathead River. The 2005 index count of 144 redds in the eight standard stream sections is eight redds higher than last year. Biologists encountered poor conditions related to high flows during counts in Whale and Trail creeks in the North Fork and Morrison and Ole in the Middle Fork. Beaver dams created partial blockages in Coal, Whale, Morrison and Granite creeks. In Granite Creek beaver dams and extremely low flows during the migration period, kept adult bull trout from reaching practically all of the traditional high density-spawning habitat.

Swan Lake Population: This is the 24th year of the bull trout redd counts in the Swan Drainage. The four annual index stream sections had 402 redds this year, which is about 30 less than the previous three years. There were very poor conditions for the counts in Lion and Elk creeks and surveyors may have missed some redds. Over the previous 23 years, our index count has averaged 390 redds, ranging from 109 to 612. Extensive beaver activity was documented in all four index sections this year.

Hungry Horse Reservoir Population: The four Reservoir index streams have averaged 75 redds annually over the past 12 years. The 2005 total of 64 is approximately 15 percent below average. Conditions were extremely poor during the Sullivan Creek survey and less than optimal in Wheeler and Quintonkin creeks. Surveyors could easily have overlooked redds in the poor lighting and high flow conditions.

Weaver said that the extended drought with low spring runoff during the past several years has allowed extensive beaver dam complexes to grow continuously. The presence of multiple dams in many of the index streams, combined with extremely low flows throughout the spawning period, now prevents adult bull trout from reaching portions of their historic spawning habitat. Heavy rains fell just as this year's spawning subsided in early October. These rains brought stream flows up to the point where counts became much more difficult, but not high enough to flush out fine sediment or breach beaver dams.