Cooperative Fish and Wildlife Research Units Program: Montana Fishery
Education, Research and Technical Assistance for Managing Our Natural Resources

Montana Fishery Project

Improving conservation status of arctic grayling; assessing and increasing landscape connectivity benefits of denil fishways in the Big Hole River

August 2017 - December 2019


Participating Agencies

  • US Geological Survey

Recovering and improving the conservation status of Arctic Grayling populations are USFWS Region 6 priority goals. The Arctic Grayling is a species of special conservation concern, and a Candidate Conservation Agreement with Assurances program was established in the Big Hole River Watershed to facilitate conservation in 2006. Barriers, such as irrigation diversions, may limit the movement of Arctic Grayling; Arctic Grayling in the Big Hole Watershed move 60-80 miles throughout the year to reach spawning, refuge, and feeding habitats. Conservation actions, such as ensuring landscape connectivity, taken before a species is listed or its habitat lost can provide simpler alternatives to expensive litigation and recovery programs. Arctic Grayling are an iconic and important component of our aquatic fauna; their presence means that quality riparian habitat remains intact to support other aquatic species. The Arctic Grayling population above Great Falls, Montana, has declined significantly. Improving the conservation status of the Arctic Grayling population that resides in the Big Hole River Watershed is important to the species overall conservation status. Hydraulic structures such as irrigation diversions are common to the river systems in Montana. They are essential for providing water diversion for agriculture but can be barriers to Arctic Grayling and other aquatic species. For over a decade, the United States Fish and Wildlife Service (USFWS), Montana Fish, Wildlife and Parks (MTFWP), USDA-Natural Resources and Conservation Service (NRCS) Montana, Montana Department of Natural Resources and Conservation (DNRC), local ranchers, NGOs, and others have worked to balance agricultural needs with the conservation of native fish, rivers, and streams. This partnership is a model for how conservation and agriculture can be blended to maintain and ideally improve both. Denil fishways have been installed in irrigation diversions throughout the Big Hole River Watershed to provide fish passage, with more fishways planned in this watershed and others. They are either included as part of the standard design and installation for new diversions or are installed as a retrofit to existing diversions. The Denils are made of steel, are 2 ft. in cross section, and are either 6 ft. or 12 ft. in length. They are typically installed into the pin and plank portion of the diversion with a total vertical drop of 1 ft. The effectiveness of these fishways has not been assessed and design criteria remain untested. Conservation partners need to know the efficiency of fish passage for Arctic Grayling and other aquatic species and their economics and water usage. Lack of assessment limits our ability to use an adaptive management strategy that might lead to better design features; partners maybe missing opportunities for win-win conflict resolution scenarios such as developing criteria that might increase passage success and landscape connectivity while providing more economical use of water when it is scarcest.