Bull-trout spawning-bed counts remain stable

Bull trout populations in Northwest Montana appear to be stable, according to the results of the state fishery program’s annual count of the protected species’ nests, called “redds.”

Officials from Montana Fish, Wildlife and Parks’ Fisheries Division hit rivers and streams last October, wading through nearly 300 of miles of water over hundreds of hours to estimate the current levels of spawning-age bull trout for six river systems.

Fisheries Manager Mark Deleray said the results indicate little overall change in the population over the past 10 years.

“It’s a glass half-full, half-empty situation,” Deleray said. “They’re not declining, which is really good. And some of these populations are really strong.”

Redds counted in the Flathead Lake drainage were down slightly in 2014 from the 10-year average, at 183 compared with 195. The count showed North Fork streams down to 51 from an average of 90, while the Middle Fork jumped to 132 from its average of 105.

The South Fork’s reservoir count was not completed, but counts in that drainage’s Bob Marshall Wilderness streams showed the average of 304 decrease to 265. Likewise, Swan Lake dipped to 428 from an average of 511. Whitefish Lake, averaging 11 redds, had 14.

The Kootenai River count held close to the average of 2,134 redds, with 2,027 last year. Wildlife officials in British Columbia assisted with this count because more than 90 percent of  bull trout spawning occurs north of the border.

While most of the numbers were down slightly, Deleray stressed that year-to-year totals do not indicate a trend, hence the agency’s focus on 10-year averages to establish an idea of the trout’s overall abundance.

Bull trout are native to many waters west of the Continental Divide, but the introduction of non-native mysis shrimp caused a dramatic decline in bull trout’s population in many river systems. Shrimp populations exploded, fueling a boom in lake trout numbers, an introduced species that quickly outcompeted bull trout.

The result for Flathead Lake was a drastic decline in bull trout, cutthroat trout and kokanee salmon. Deleray said by the 1990s the numbers from annual counts showed the bull trout population down to less than a quarter of historic levels. An Endangered Species Act listing of “threatened,” fishing prohibitions and other conservation measures brought those numbers back up to about half of historic levels by the new millennium, where they appear to have stabilized.

“We’re at twice the level we were in the ’90s. The bad news is they’re half the level we had historically,” Deleray said. “We basically had two different lakes. A lot of people want to go back to the ’80s [but] there’s no way to go back to the ’80s. It’s completely changed.”

Beginning in late summer, bull trout begin an annual migration upstream from Flathead Lake, staking out spawning grounds in tributaries of the North and Middle forks of the Flathead River. In September, the females carve out large depressions in the stream beds to lay their eggs. Deleray said the trip proves extremely exhausting for the fish, the majority of which only spawn once.

“Some of these fish will migrate 130 miles,” he said. “It takes a huge amount of energy not only to make those runs, but the males are fighting with each other and the females are digging out these redds.”

The counters can easily identify the shallow underwater pits by the bright color on the overturned rocks, contrasted against the algae and dirt overlaying the surrounding stream bed. 

The Flathead portion of the redd count covers sections of eight main tributaries used by bull trout from Flathead Lake and accounts for about 45 percent of the total nests in that drainage area. Bull trout populations are evaluated separately in other drainages such as the South Fork and Swan Lake, where dams impede spawning activity.

In addition to collecting redd numbers, counters have also come across signs of illegal fish poaching, although Deleray noted these practices appear to have declined in recent years.

“There’s evidence annually; we’ll find makeshift spears and makeshift dams trying to trap them,” he said. “You can see how vulnerable they would be.”

Reporter Samuel Wilson may be reached at 758-4407 or by email at swilson@dailyinterlake.com.