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Big Hole, Beaverhead, Ruby Trout Declines Prompt Research

Montana Fish, Wildlife & Parks in partnership with the Montana Cooperative Fishery Research Unit at Montana State University is seeking to get to the bottom of what is ailing the Big Hole, Beaverhead, and Ruby rivers with their declining trout populations as well as disease. In particular, three research projects will aim to determine what is affecting fish abundance and a fourth study, conducted by FWP, will look at fish health and building capacity to sample fish for diseases.

The three studies with MCFRU will focus on adult mortality, juvenile origins and survival, and fish diseases. Since 2011, trout numbers in these rivers have steadily declined and are now near historic lows. While those declines are certainly linked to low flows and warm water temperatures, the research projects will take a more in-depth look at other factors that may be affecting these fisheries.

The adult mortality study will involve tagging and tracking fish. FWP staff will capture and tag fish on the Big Hole, Beaverhead and Ruby rivers, along with the Madison River. The project will assess how flows, water temperatures, angling and disease influence survival. As part of the study, fish biologists Matt Jaeger and Jim Olsen are developing adaptive management plans that will inform fishing regulations on the Big Hole, Beaverhead and Ruby rivers. This could include spawning closures and catch-and-release as examples.

The juvenile study will look at where fish are born and their spawning and rearing habitat, mostly in tributaries. Biologists will sample the fish’s otolith, or ear bone, to determine where the fish has lived and traveled during its life. This work will help focus and direct potential habitat projects.

The third project will examine the level that disease is impacting trout populations on these three rivers. It will include testing for novel pathogens and help determine better ways to routinely sample fish for disease in the future.

The public can participate in fish health monitoring by reporting dead and sick-looking fish on the new web portal

For more information and to follow the progress of the research projects, visit


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