Brown Trout: What’s Up?

Despite bad news about Big Hole brown trout, I was lucky enough to catch this beautiful brown trout the day after the TU meeting discussed below.

“There’s not a lot of good news,” is not what people wanted to hear, when Montana Fish, Wildlife & Parks fisheries biologist Jim Olsen began his presentation to the George Grant Chapter of Trout Unlimited on May 12. 

 The gathering actually drew an in-person audience, for a change, with covid-19 restrictions loosening, though some people took in the program at their home computers.

 Olsen is the biologist assigned to the Big Hole River and its watershed, and he reported on the latest data from electrofishing surveys done this spring, adding this year’s information to almost 50 years of sampling data.

While he reported on survey results on several stretches of the river, the Melrose to Browne’s Bridge stretch was typical of what’s happening.

 Both brown trout and rainbow trout have been on a decline in the last several years, and he’s trying to figure out what is going on that’s causing the decline. This stretch was hit by a saprolegnia (a water mold disease) outbreak in 2014 that caused a temporary decline in fish numbers, especially brown trout. After a dip, numbers rebounded in 2016. Since then, fish numbers, both brown trout and rainbow trout have been declining. Olsen noted that whirling disease has been affecting rainbow trout in this area.

 Currently, surveys indicate trout populations of around 400 brown trout and 400 rainbow trout per mile. A troubling statistic is that age two fish are only around 100 per mile.

 Olsen summarized his presentation with known information. There is currently poor recruitment (fish surviving to adulthood), no significant disease factors, and by and large the fish are strong and healthy. Warm weather begins sooner in spring and lasts longer into autumn. Significantly, angling pressure is way up. Olsen has been working the Big Hole since 2008 and total angler days per season has doubled during this time to nearly 90,000 angler days annually.

 He adds that there is no real data on fish harvest though he believes that some 90 percent of fish caught are released, though there is always some mortality with catch and release. He suspects that angling pressure is affecting fish populations, especially damage to spawning redds which are highly vulnerable. He also notes that other rivers in southwest Montana have similar issues.

 In response to an audience suggestion of stocking fish, Olsen responded that FWP’s commitment is to manage habitat for wild fish, not stocking.

 Olsen says he is considering making a recommendation to the Montana Fish & Wildlife Commission to return to a regular closed season on the Big Hole, as the doubling of angling pressure is a statistic that stands out in looking at changes to the fishery.

  Olsen also reported on efforts to restore French Creek to a native fishery. The entire watershed was treated with a first dose of rotenone in 2020, and a second dose will be done in 2021. If DNA testing in 2022 shows that efforts to get rid of non-native fish are successful, they will begin stocking westslope cutthroat trout in 2022.

 Caleb Uerling, who became fisheries biologist for the Upper Clark Fork watershed in 2019, reported on low trout numbers in the upper Clark Fork River, though trout numbers are improved slightly from a low in 2019, including some small populations of cutthroat trout.

 He also had some intriguing data on the Little Blackfoot River, with fish numbers ranging from 600 to 1100 per mile, including both brown trout and cutthroat trout. Most intriguing was a pair of photos of a large brown trout that showed up in electrofishing in almost identical locations in two consecutive years, growing from 25 inches to 26 inches during that time.

 I’ll close by reporting that the following day, I went out on the Big Hole with a Dillon friend, Ray Gross, floating the Melrose stretch. I caught just two fish for the day, one a 10-inch rainbow and the other a gorgeous brown trout that may well be my best trout of 2021.

 We were somewhat frustrated by the lack of fish action, but we can’t make the fish bite. Still, that big brownie certainly made the day a success.

 Paul Vang’s new book, “Golden Years, Golden Hours,” is available at How Novel, The Second Edition, Isle of Books & Books, or online at

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