Biologists disagree over bull trout health in Flathead

Two biologists from two different government agencies agree on one thing — bull trout numbers in the Flathead appear to be stable. But they differ on the future of the native fish.

Montana Fish, Wildlife and Parks biologist Tom Weaver says bull trout redd counts show a stable population over the past 10 years, and some spawning streams in the North Fork, particularly Coal Creek, saw a surge in numbers this year.

Biologists count spawning beds, called redds, each fall to gauge how many adults are returning to streams each year and the overall health of the bull trout population. The higher the count, the more robust the population.

This year, biologists counted 225 redds in the North Fork and Middle Fork tributaries, compared to 229 last year and 189 one year earlier. But those numbers pale in comparison to the early 1980s when numbers ranged from 300 to as many as 600 in 1982.

Twenty-three redds were found in Coal Creek this year, a significant rebound from 2009 when none were counted. Weaver said he believes redd numbers were low or zero in Coal Creek that year because biologists — himself included — handled the fish too much during research in the 1980s and 1990s. As a result, the adults died. A bull trout reaches maturity at age 6 or 7, which would help explain gaps in the redd counts, he noted.

“They’re called bull trout, but they’re very fragile,” he said.

Meanwhile just to the south, Big Creek continues to lag behind, U.S. Fish and Wildlife Service biologist Wade Fredenberg said. This year, just eight redds were found in Big Creek, compared to 40 in 2007. But the numbers have fluctuated — in 1984, only nine redds were counted, and lake trout weren’t nearly as big a problem back then.

Fredenberg suspects the smaller population results from Big Creek being closer to Flathead Lake, where bull trout have a tough time competing with non-native predatory lake trout. And future numbers could be worse.

“Modeling would suggest that over time (streams with low numbers) aren’t going to come back — they’ll blink out,” he said.

Biologists still aren’t exactly sure if lake trout eat small bull trout or if lake trout just out compete them for food, Fredenberg said. But biologists do know this — the two fish don’t mix. When lake trout and bull trout are in the same lake, the non-native lake trout win out hands down.

Fredenberg said the FWS supports suppression of lake trout in Flathead Lake, and if gill netting proposed by the Confederated Salish and Kootenai Tribes is the best way to do it, then so be it.

Weaver doesn’t support the gill netting proposal. Smaller lake trout able to avoid the nets could end up feeding all the more on bull trout, he said.

Fredenberg disagreed. That would be the case if netting targeted just big fish, but the nets will target all lake trout, he said.

Weaver is also worried about bycatch. Gill netting doesn’t discriminate, he said — any fish that swims into one is dead. He said he supports current management of the lake, which includes the Mack Days fishing derbies that suppress lake trout numbers each year.

But Fredenberg points to lake trout suppression efforts at Lake Pend d’Oreille in Idaho, where lake trout have been netted for about six years, and kokanee salmon and bull trout numbers are much better.

Anglers may find out soon enough. CSKT continues with plans to implement a netting program, at least on the south half of the lake where it has jurisdiction.