FWP and MSU continue partnering on four studies

Montana Fish, Wildlife & Parks has wrapped the 2025 field season for trout research in southwestern Montana. Over the last eight months, researchers have spent hundreds of hours talking to anglers, counting fish, taking tissue samples, analyzing results and compiling data all in a focused effort to better understand what is affecting fish populations in some of Montana’s most prized fisheries.

The research effort is part of a multi-year partnership between Montana State University and FWP. The focus of the joint effort is four studies: trout recruitment in tributaries and how it contributes to mainstem populations, major limiting factors of mortality for adult trout, and recreational use including angler success and harvest across the study area. The fourth study, led by the Big Hole Fish Health Workgroup, is focused on better understanding the potential causes and effects of head lesions and fungal infections most often observed on brown trout and mountain whitefish in the three rivers above.

Interim summaries from these studies will be posted on FWP’s website as they become available in the coming months.

“We’re confident this focused research effort will provide us key insights that we’ll adopt into management plans moving forward,” said Quentin Kujala, FWP chief of conservation policy. “We can’t pull off an effort like this without the ongoing support and participation of anglers, who we know are just as passionate about these rivers and the fisheries as we are.”

The four studies were prompted by trout population estimates in 2023 that were at or near historic lows in portions of the Big Hole, Beaverhead and Ruby rivers.

Juvenile recruitment study

This year MSU staff sampled juvenile trout in 12 tributaries to the three rivers. They also sampled juvenile trout as part of abundance estimates in several mainstem sections. Some of the mainstem trout analyses includes otolith microchemistry, which uses inner ear structures in fish to determine which waterbody each fish hatched in, when the fish entered the mainstem rivers and important movement corridors within the watersheds.

This research will inform efforts to improve conditions in tributaries and specific mainstem reaches that are or have potential to contribute to mainstem trout populations. Such efforts will include continuing to work with water users to improve flows and enhancing spawning and rearing habitats to improve juvenile trout survival in important streams or mainstem areas.

Adult mortality study

FWP staff tagged trout in the Big Hole, Beaverhead, Ruby and Madison rivers again this year, which offered another opportunity to recapture fish that were tagged last year. This sampling, as well as reports from anglers who catch tagged fish, helps researchers identify individual fish and monitor their health, survival, movements and other indicators over time.

Anglers who report catching tagged fish are substantively contributing to the informed management of these fisheries. FWP and MSU have been working with Montana Trout Unlimited to host regular drawings for anglers who submit these reports. Prizes such as guided fishing trips, gear, artwork and other giveaways have gone out to dozens of anglers, including three anglers who were awarded prizes this month. To date, MSU staff have awarded $100 for each of the 122 cash reward tags that have been reported by anglers. These drawings will continue, including a year-end prize drawing among all anglers who submitted a tagged fish report in 2025.

Researchers are asking anglers to continue clipping tags off of fish caught in these rivers, then submitting a report for each tag. If you catch a fish with two tags, please remove and report both tags to MSU’s website. To submit a report, click here.

Fish health

FWP staff continue to monitor fish health after sick fish were reported in the Big Hole, Beaverhead and Ruby rivers in 2023. Since then, reports and sightings of sick fish have declined. Monitoring efforts during spring and fall sampling efforts indicate prevalence to be less than 1 percent of the fish handled by FWP staff in 2024 and 2025. However, reports of sick and dead fish typically peak during the summer when conditions are not suitable for sampling because of high water temperatures and low flows.

Although no potential causes of the head lesions or fungal infections have been identified by the Big Hole Fish Health Workgroup, FWP staff and partners continue to pursue testing that will identify or at least rule out potential pathogens or other causes. FWP plans to further support fish health concerns and needs through additional staffing that was approved during the 2025 Montana Legislature. This includes hiring a disease ecologist to study fish health and a technician to help with sampling across the entire state.

River recreation study

A recent increase in recreational floating has prompted a fourth study examining how use on rivers affects the quality of recreationists’ experiences and the impacts to infrastructure, such as fishing access sites. FWP and MSU staff are interviewing recreationists on the Big Hole, Beaverhead, Ruby, Madison and upper Yellowstone rivers. The study aims to better characterize overall use on and around rivers to help FWP and partners provide the best recreational experience possible while protecting the resources Montanans enjoy. Those efforts are being led by creel clerks who interview recreationists while they’re out enjoying the water. Important insight into angler catch rates and harvest will help inform the adult mortality study as well as the adaptive management plans that FWP staff continually refine based on new information. To review those specific plans as well as the entire Statewide Fisheries Management Plan, which is scheduled to be updated next year, click here.

“We greatly appreciate anglers and other recreationists who are contributing to these studies,” said Mike Duncan, FWP’s fisheries program manager in southwestern Montana. “Their continued support will make informed solutions possible for sustaining these cherished resources.”