Bull trout redd numbers mostly stable
By Moosetrack Megan

Posted: December 20, 2015

Montana Fish, Wildlife & Parks (FWP) Fisheries field crews have completed the annual inventory of bull trout spawning sites in the Flathead, Clark Fork and Kootenai drainages, which comprise northwest Montana’s FWP Region One. Experienced observers walk known spawning areas and count the number of spawning nests called redds. Female bull trout excavate a depression in the streambed, deposits her eggs, which are immediately fertilized by a male, and then covers the fertilized eggs with clean gravel. These nests are typically four to six feet long by three feet wide, and easily identified. Redd counts are indicative of the abundance levels of spawning adult bull trout each year and used to assess status of bull trout populations in northwest Montana.

According to FWP Bull Trout Specialist Tom Weaver, low stream flows created shifts in spawning locations during the 2015 counts in some river drainages in Northwestern Montana. “In some streams our annual index sections were not accessible to fish due to debris jams, beaver dams, or other flow related conditions, resulting in lower than expected counts,” says Weaver. He noted that as time allowed, crews conducted additional surveys downstream from the normal index reaches to confirm if spawning runs had been blocked.

“With the exception of portions of the Kootenai, bull trout redd numbers were stable for all basins similar to 10-year averages,” says Weaver. Region One Fisheries Program Manager Mark Deleray adds that his staff and cooperators put in a significant amount of field time to collect these data every year. Avista, Bonneville Power Administration and the Department of Natural Resources and Conservation (DNRC) provide funding assistance. Glacier National Park, the US Forest Service and Plum Creek Timber Company assisted with field counts. “It’s important to have the actual field counts as there is considerable agency and public interest in bull trout population status since they were listed under the Endangered Species Act,” says Deleray.

Deleray noted that bull trout redd counts provide a means to assess the status of bull trout populations over time, and that one year’s count alone is not indicative of a population trend. Rather, these redd counts provide an annual basis for bull trout conservation discussions among fisheries professionals and angler groups.

The following is a summary of the status of bull trout redd counts in the drainages of northwest Montana:

Flathead Lake: This was the 36th year of annual FWP index counts for Flathead Lake bull trout. The index count consists of parts of eight streams and is a partial count for the basin.
FWP personnel, with help from Glacier National Park staff survey parts of four North Fork
and four Middle Fork tributaries each year. The count in the four North Fork streams over the past 10 years has ranged from 51 to 144, averaging 86 redds. The 2015 count of 50 is below this 10 year average, but similar to the counts of 54 in 2010, 58 in 2012 and 51 last year. We had an extremely low count in the Big Creek index section this year (1 redd), which caused concern. When a supplemental survey in Hallowat Creek, a tributary which typically contains a portion of this drainage’s spawning resulted in no redds, we suspected a blockage downstream. Since the Moose and Robert fires, a log debris accumulation has formed approximately one mile downstream from the lower end of our index section. An additional survey of this area found new gravel deposition and channel braiding, with extensive beaver activity which blocked most upstream migration. We observed 20 redds in the area below the blockage, which has not contained suitable spawning habitat prior to the recent channel changes. In additional surveys conducted outside of the four North Fork index reaches, FWP fisheries teams counted over 130 redds in the Canadian North Fork and others in additional Montana North Fork tributaries.

Counts in the four Middle Fork reaches have ranged from 56 to 171 over the past decade, averaging 114 redds. The current count of 132 is identical to last year, higher than seven of the past 10 years and 16% above average. The high Middle Fork index counts in recent years are similar to the counts in the 1980s.

When combined, the eight stream index count of 182 is under the average number (200) observed over the past 10 years, and the second lowest in that time period. Again, low flows, barriers and the additional 20 redds found downstream from the standard index section in Big Creek, which are not included in this year’s combined total of 182, makes the 2015 total closer to the ten year average.

Every three to five years crews count all 33 stream sections in the North and Middle forks that are known to support bull trout spawning. This includes streams of the North Fork in British Columbia, additional Middle Fork streams in Glacier National Park and in the Great Bear and Bob Marshall Wilderness areas. These basin-wide total counts have shown that the eight index sections support about 45% of the annual bull trout spawning run out of Flathead Lake and allows us to estimate total redd numbers with a high degree of confidence. Using the 2015 index count of 182 redds, we estimate a basin-wide total of 404 this year. If the Big Creek number is adjusted, the basin-wide estimate would be 449 redds. Overall, redd counts for Flathead Lake are stable.

Hungry Horse Reservoir/South Fork: In the South Fork, FWP has annually counted four tributaries draining directly into Hungry Horse Reservoir for the past 23 years. These streams support just under 20% of total spawning in the South Fork drainage. The 2015 count of 52 redds for the reservoir index sections is below the ten year average. Considering the extremely low flow conditions this fall and the resulting changes in habitat conditions observed elsewhere, some spawning may have occurred downstream from the annual index sections, but timing constraints did not allow for additional surveys. The 2015 bull trout net catch of 9.1 fish per net in Hungry Horse Reservoir was the second highest on record. In general, redd numbers in the South Fork are stable.

Field crews have surveyed four Wilderness backcountry spawning streams10 times since initiated in 1993. A basin-wide count in the South Fork Drainage requires in excess of 60 worker days and ten head of stock for backcountry sections. Expanded backcountry counts are tentatively planned for 2017.

Swan Drainage: Index counts in four stream sections in the Swan Drainage have been completed annually for the past 34 years. With field assistance of Plum Creek Timber Company and US Forest Service personnel and partial funding from DNRC, we have completed basin-wide surveys in the Swan annually since 1995. This includes our four index sections plus an additional six stream sections. While this year’s basin-wide total of 421 redds is below the average over the last decade (494), it is similar to last year’s total of 428. In the recent seven years, Swan Drainage redd counts appear to have stabilized around this lower level. Although identification of the exact mechanism is difficult, reductions in the number of redds in the Swan drainage are likely the result of competition/predation from lake trout and netting bycatch bull trout mortality from the interagency lake trout suppression experiment.

Upper Stillwater and Whitefish Lakes: Upper Stillwater Lake and Whitefish Lake support bull trout populations which are distinct from the larger systems in the Flathead Basin. Bull trout from Upper Stillwater Lake spawn in the Stillwater River. Those from Whitefish Lake spawn in Swift Creek and the West Fork of Swift Creek. FWP fisheries biologists have monitored these populations in cooperation with the DNRC for the past 22 and 23 years respectively. The 2015 count of 45 redds for the Stillwater River is the highest in the last 10 years. The 2015 Whitefish Lake count of 11 is equal to the 10-year average. Redd numbers appear stable.

Lower Clark Fork: Bull trout inhabiting the lower Clark Fork River and the reservoirs behind Thompson Falls, Noxon Rapids and Cabinet Gorge Dams spawn in accessible tributaries from the Thompson River downstream to Cabinet Gorge. Data in the attached table come from tributaries to the Clark Fork River from the Thompson River downstream to Idaho. FWP-led field crews have monitored spawning runs in these streams annually over the past 15 years. The 2015 count of 70 redds is lower than the annual average. Overall redd numbers are stable. In some cases bull trout redds were found outside of monitoring reaches because of low water. These redds were not included in the index count. Approximately 18 accessible tributaries from eight major drainages are monitored annually by crews from FWP, AVISTA Utilities, Plum Creek Timber Company, and the US Forest Service.

Kootenai Drainage: Over the past 21 years, bull trout redd counts have been completed by FWP and Canadian fisheries biologists on the Wigwam River and three other Kootenai River tributaries in Canada, the Grave Creek Drainage, the Quartz Creek Drainage, O’Brien, Pipe, Bear, the West Fisher and the Callahan Creek Drainages. Bull Lake supports a separate population which spawns in the Keeler Creek Drainage. This effort includes assistance from British Columbia and Idaho Fish and Game. The vast majority of bull trout from Koocanusa Reservoir and the Kootenai River upstream spawn in the Canadian tributaries. These tributaries in British Columbia accounted for an average of over 90% of the annual spawning in the Kootenai Drainage.

The 2015 counts for Koocanusa Reservoir spawning tributaries including the Grave Creek drainage, Wigwam River drainage, Skookumchuck River and White River drainage in British Columbia were within the range observed over the past decade and higher than the last several years. Counts by FWP staff in spawning streams downstream of Libby Dam toward Kootenai Falls including the West Fisher, Quartz, Pipe, and Bear creek drainages were considerably lower than average, as were those in tributaries downstream from the falls to the Idaho border. Extremely low flows resulted in passage problems, including both partial and potentially complete debris jam barriers, enhanced beaver related impacts and an overall reduction in quality spawning habitat availability. Additionally, historic spawning site gravels have been removed through flow events and not replaced due to debris jams. The lowest count on record in the Keeler Creek Drainage is likely influenced by an expanding northern pike population in Bull Lake.