BOZEMAN – Montana Fish, Wildlife & Parks recently completed its annual report to NorthWestern Energy for the Madison River drainage.
Through its Federal Energy Regulatory Commission (FERC) license, NorthWestern Energy provides mitigation funds to protect and enhance Madison River basin fisheries. FWP’s report details how these mitigation funds were used in 2020 to complete fish population monitoring in Hebgen Lake and in two sections of the Madison River.
FWP uses these estimates — which have been conducted since the 1960s — to monitor the health of the river’s trout populations.
Last year, biologists found that the number of brown and rainbow trout at least 6 inches long remained below the 20-year averages in the upper Madison River, except for rainbow trout in the Varney section, which runs from Varney Bridge to just above the Eight Mile Ford Fishing Access Site.
There, biologists found an estimated 2,401 rainbow trout per mile, the highest abundance observed in more than 20 years. However, the majority of these fish — more than 2,000 per mile — were age-1 rainbow trout, and only 250 fish per mile were over 11 inches long. Estimated abundances of brown trout in the Varney section remained relatively stable for the fourth consecutive year at 1,339 fish per mile, which is 82 percent of the 20-year average for the section.
In the Pine Butte section, which is the 3.5 miles of river upstream of Lyons Bridge, biologists found an estimated 2,152 rainbow trout per mile, which was similar to 2019 estimates. However, brown trout in that section declined by about 15 percent from 2019 to 1,367 fish per mile. The abundance of rainbow and brown trout over 11 inches long declined from 2019 estimates.
Biologists used gill nets to estimate the abundances of trout in Hebgen Lake. Estimated abundances of both rainbow and brown trout declined in Hebgen Lake in 2020, but they remain near long-term averages of 12.9 brown trout per net and 6.3 rainbow trout per net.
NorthWestern Energy mitigation funds were also used to complete a creel survey on Hebgen Lake in March by gathering information on angler satisfaction and catch rates. This, along with data gathered from gill-netting efforts, will help inform fisheries management of Hebgen Lake.
To see the full report, please visit go.usa.gov/x6yMf.