Spawning surveys show positive results

Montana Fish, Wildlife and Parks reports that bull trout spawning surveys in eight tributaries of the North and Middle forks of the Flathead River had encouraging results.

FWP completed the surveys between Oct. 1 and 10. Biologists counted the number of “redds” or nests made in streambed gravels by adult bull trout from Flathead Lake. This is the best estimate of the mature bull trout spawning run from Flathead Lake.

Identical sections are counted annually and represent a known portion (about 45 percent) of the total bull trout spawning in the drainage. The entire drainage is counted every three to five years. This was the 33rd consecutive year of index counts for the Flathead Lake bull trout population.

This year’s basin-wide estimate of 500 redds indicates a stable bull trout population. The counts have been relatively stable over the past 15 years (about three generations of bull trout), averaging 434 redds.

This year’s estimate of 500 redds is 66 percent above the minimum secure level of 300 redds calculated under the Flathead Lake and River Fisheries Co-Management Plan. Based on the average number of eggs per female, this translates to several million eggs deposited in the North and Middle fork tributaries.

The estimate of 500 redds is 57 percent of the 1980s average but twice as high as the low level reached in the mid-1990s. FWP called this rebound encouraging and indicates the current bull trout population is relatively stable.

Mature bull trout migrate upstream from Flathead Lake in the summer, spawn in September and then return to Flathead Lake in October. The young fish hatch and then live in the tributaries from one to three years before migrating downstream to Flathead Lake, where they grow to adults and complete their life cycles. Biologists estimate about half the adult bull trout in Flathead Lake spawn each year.