Biologists find no surprises in bull trout counts

According to Montana Fish, Wildlife and Parks Region 1 fisheries program manager Mark Deleray, there were no surprises in the 2014 bull trout redd counts for the Clark Fork, Flathead and Kootenai river drainages in Northwestern Montana.

“Bull trout redd numbers appear stable in all basins, being very similar to 10-year averages,” he said. “In each basin, this year’s count may be slightly higher or lower than last year’s, but not significantly different than recent years.”

Experienced fisheries field crews walked known spawning areas and counted the number of spawning nests called redds. Female bull trout excavate a depression in the streambed where they deposit their eggs, which are immediately fertilized by a male.

The redds are typically four to six feet long by three feet wide and are easily identified when walking down the stream channel. Redd counts indicate the abundance of spawning adult bull trout each year and are used to assess status and trends in bull trout populations in Northwest Montana.

One year’s count alone is not indicative of a population trend, Deleray noted. Redd counts instead provide an annual basis for bull trout conservation discussions.

This was the 35th year for the Flathead Lake bull trout count, which is a partial count for the basin. The 2014 count in the four North Fork streams was 43 percent below the 10-year mean, but similar to counts in 2010 and 2012. The 2014 count in the four Middle Fork reaches was higher than in seven of the past 10 years and 26 percent above average.

Every three to five years, crews count all 33 stream sections known to support bull trout spawning in Flathead Lake, including the upper mainstem of the North Fork and six of its tributaries in British Columbia, two additional Middle Fork streams in Glacier National Park and 10 other Middle Fork tributaries in the Great Bear and Bob Marshall wilderness areas.

These basin-wide counts have shown that the eight index streams support about 45 percent of the annual bull trout spawning run out of Flathead Lake, which allows fisheries biologists to estimate total redd numbers with a high degree of confidence. Using the 2014 index count, they estimate redd counts for Flathead Lake appear stable.

Each year for the past 22 years, FWP has counted redds in four tributaries that drain directly into the Hungry Horse Reservoir and support about 20 percent of total bull trout spawning in the South Fork drainage. While the 2014 count is 15 percent below what’s been observed over the past 10 years, redd numbers in the South Fork appear stable.

Annual index counts in four stream sections in the Swan River drainage have been completed for the past 32 years. While this year’s total is 16 percent below the average over the past decade, it does represent a considerable increase over the 2013 count, biologists concluded.

Since 2009, efforts have been made to reduce the population of non-native lake trout in Swan Lake. Although identification of the exact mechanism is difficult, reductions in the number of redds in the Swan drainage were likely the result of competition or predation by lake trout, or a result of netting bycatch mortality from the lake trout suppression project.

Upper Stillwater Lake and Whitefish Lake support bull trout populations are not part of the larger systems. FWP has monitored these populations in cooperation with the Department of Natural Resources and Conservation for the past 18 and 20 years. The 2014 counts in both of these lake systems were very similar to the average over the past 10 years, and redd numbers appear stable, biologists concluded.