Clark Fork River brown trout in decline

Brown trout decline in Clark Fork River above Deer Lodge

Brown trout aren't doing so well in Montana's upper Clark Fork River.

Montana Fish, Wildlife and Parks fish surveys show a steady trend of declining brown trout numbers in the Clark Fork River upstream of Deer Lodge.

Brown trout are the predominant trout species in this stretch of river and are surveyed annually. Recent surveys show a declining trend, particularly near the Warm Springs area.

FWP, the Montana Department of Environmental Quality (DEQ), the U.S. Environmental Protection Agency (EPA) and the Montana Natural Resource Damage Program (NRDP) are working together to understand more about the cause of decline and what can be done to reverse the trend. 

The Upper Clark Fork has a long history of impacts that have affected the fishery.  Current remediation (mining metals cleanup) efforts are addressing some of the water quality problems related to heavy metals. However, there are many other variables impacting fish such as structural habitat, river flows, and water temperature.  These variables can be important not only in the main stem of the Clark Fork River but also in its tributaries.

The Upper Clark Fork is a complex system with a long history of degradation and, more recently, recovery. This adds to the challenge of sorting out the causes of the fish decline. The partner agencies recently met in Missoula to identify how best to continue meeting this challenge. The overall goal is effective remediation and restoration of the area.

Partners are currently revisiting existing data to better understand decreased juvenile fish recruitment into the population, which seems to be the biggest driver for the decline. They are also prioritizing what other questions need to be addressed with additional research.

“To find what factors are limiting recruitment and overall trout numbers, we all need to share our resources and knowledge,” said Nathan Cook from NRDP. “Addressing issues currently impacting the trout population is part of Montana’s overall restoration goals for the Upper Clark Fork.”

In recent years, partners have worked on habitat projects that provide some short-term streambank improvements while waiting on longer-term natural recovery mechanisms that will help the fishery into the future. Additionally, NRDP continues to allocate restoration funds to projects in priority Upper Clark Fork tributaries, aimed at increasing juvenile fish recruitment contributing to the mainstem population.  

“Rather than a single or simple cause, stressors may vary between seasons, location and fish life stage,” said Pat Saffel, FWP regional fisheries manager. “We’re all coming together to learn as much as we can, so that we can continue making informed management adjustments to help the fishery.” 

Saffel says that FWP and partners will provide updates as research and work in the Upper Clark Fork continues.