BOZEMAN – Montana Fish, Wildlife & Parks, in partnership with Montana State University (MSU), have brought on new staff and students in preparation for this year’s field season to study rainbow and brown trout declines and fish health concerns in the Jefferson Basin.

FWP recently hired a new fisheries technician based in Dillon to support efforts in the Big Hole, Beaverhead, Ruby and Madison rivers, including upcoming studies with MSU. That work will include three PhD students and support staff who will begin studies on recreational use, adult trout mortality and juvenile trout recruitment in 2024 on the four rivers.

FWP and MSU staff and students are meeting regularly to prepare for the upcoming field seasons. FWP staff will continue to provide regular updates on these projects through news releases and public meetings.

“We’re looking forward to beginning this important field season this spring,” said Mike Duncan, FWP’s fisheries program manager in southwestern Montana. “We’re grateful for the partnerships that will make these studies possible as we work toward solutions to the issues we’re seeing for fish in the Jefferson Basin.”

Fish health update

In the Big Hole and Beaverhead rivers, FWP staff and anglers have observed clinically diseased adult fish with apparent increasing frequency in recent years. FWP has conducted health assessments in those rivers. However, disease in fish is a complex interaction among the fish host, potential pathogens and environment, which poses challenges in determining the primary cause of fish health issues.

FWP staff have detected the parasite that causes proliferative kidney disease in the Big Hole River and many other rivers across Montana using molecular testing methods. However, staff have yet to see the disease manifest itself in fish in the river. It is also unclear whether the observed fungal infections or lesions are the primary cause or secondary effects of another disease. Thus far, testing has not identified any bacteria or viruses that are common fish pathogens.  

Tissue from diseased fish are being examined at a cellular level by pathologists from the U.S. Geological Survey (USGS) and U.S. Fish & Wildlife Service (USFWS). Results will be available this winter and will help determine the next steps in health assessments. Further testing for potential fungi, bacteria or viruses using alternative culture methods and technologically advanced molecular testing will occur this spring, summer and fall in adult and juvenile fish collected from the Big Hole and Beaverhead rivers. 

In the meantime, FWP has convened a workgroup with experts from across the country to better understand risk factors and underlying stressors influencing fish health at individual and population levels in these rivers. The workgroup will develop a proactive monitoring approach to characterize the relative contribution of potential stressors, including water quantity and quality, climate, and angling pressure that will be implemented this spring.

FWP’s partners include fish health experts, histopathologists, water quality specialists, microbiologists, fish physiologists and fish biologists with FWP, MSU, USFWS, USGS, Washington Animal Disease Diagnostic Lab at Washington State University and the USGS Montana Cooperative Fishery Research Unit.

For more information about FWP’s response to trout declines in the Big Hole, Beaverhead and Ruby rivers, visit bit.ly/3Scbf9X.