For Immediate Release:  December 2, 2025

Contact: 

• Dr. Zachary Hoylman, (406-499-8118), hydrosphere.analytical@gmail.com
• Patrick Kelly, Western Watersheds Project, (208) 576-4314, patrick@westernwatersheds.org

New Report Finds That Arctic Grayling Face Increasing Risk in Big Hole River, Despite Conservation Efforts

MISSOULA, Mont.— According to a new study submitted to the U.S Fish & Wildlife Service, Arctic grayling in Montana’s Big Hole river face increasing risk despite conservation efforts undertaken since 2017. Summertime flows continue to decrease and water temperatures are climbing due to climate change and habitat degradation, undermining any gains potentially accrued by conservation actions in the Basin.

“This analysis makes clear that the Big Hole River is warming and drying faster than current conservation efforts can compensate, leaving Arctic grayling and other cold-water species increasingly vulnerable.” said Dr. Zachary Hoylman, chief scientist with Hydrosphere Analytical and author of the study. “Without decisive action to safeguard instream flows, the Big Hole River will continue to lose the ecological integrity that made it a renowned stronghold for Arctic grayling and other cold-water dependent fish.”

The comprehensive evaluation found that the combined pressures of hotter summers and shrinking streamflows are overwhelming any potential benefits of previous management actions. When combined with the extensive irrigation withdrawals and riparian degradation already occurring throughout the Big Hole watershed, the intensifying climate change impacts identified in the report pose a serious threat to Arctic grayling, which depend on cold clean water and stable flows for growth, movement, and survival.  

“This new study has serious implications for the already struggling native Arctic grayling population in the Big Hole, as well as for other fish species in precipitous decline throughout the basin” said Patrick Kelly, Montana Director for Western Watersheds Project. “The US Fish & Wildlife Service now has the science it needs—and the responsibility—to act boldly on behalf of Arctic grayling, a species that has waited far too long for meaningful protection.”  

By integrating decades of temperature, hydrologic, and climate data, the analysis fills major scientific gaps and undermines the previous rationale for not listing Arctic grayling under the Endangered Species Act. That previous determination relied on a limited record ending in 2017 and did not fully or adequately account for the accelerating influence of climate change. As the U.S. Fish & Wildlife Service now prepares its court-ordered listing determination, the urgency of stronger and more enforceable protections cannot be overstated. The evidence shows that voluntary and small-scale conservation measures are not enough to counteract the impact of increased climate warming.

“These findings demand stronger, enforceable action, not voluntary or piecemeal measures,” said Kelly. “Protecting instream flows and restoring functional riparian zones must be treated as non-negotiable requirements for Arctic grayling survival.”

Key Takeaways and Conservation Implications of the Big Hole study:

• The river’s thermal resilience has not improved despite years of touted conservation actions. The analysis finds no measurable increase in thermal buffering since 2017, contradicting repeated assertions that past efforts have strengthened river conditions for Arctic grayling.
• The Big Hole River is warming dangerously. Climate change is driving sustained increases in summer air temperatures, which in turn are causing more frequent and prolonged warm-water stress events in Arctic grayling habitat.
  
• Summer streamflows are declining leaving river habitats hotter and more vulnerable every year. A basin-wide drop of nearly 50 CFS per decade means the Big Hole river is losing adequate flow, its most important natural defense against warming.
  
• Previous federal decisions not to list Arctic grayling did not fully account for climate change. The 2020 U.S. Fish & Wildlife Service determination relied on a truncated and inadequate dataset ending in 2017, missing the sharp increases in warming and flow decline documented in subsequent years.
  
• Arctic grayling are not alone in facing decline. Native cutthroat and introduced trout populations are also declining in the Big Hole as warm-water conditions expand and cold-water refuges shrink.

Background & Timeline:

Arctic grayling once occupied hundreds of miles of rivers in Montana’s upper Missouri River basin. By the mid-1900s, overharvest, stream diversion and flow reduction, grazing and riparian damage, dam construction, and non-native trout introductions drove dramatic declines. Today, the upper Big Hole River supports the last native fluvial grayling population in the lower 48 states.

• 1991–1994 – First formal petitions submitted to the U.S. Fish & Wildlife Service (USFWS) to list the Upper Missouri River fluvial Arctic grayling under the Endangered Species Act (ESA).
  In 1994, USFWS finds listing “warranted but precluded,” placing grayling on the candidate list.
• 1995 – Montana completes its Arctic Grayling Restoration Plan, calling for reestablishing multiple viable fluvial populations.
• 2003–2005 – Litigation forces renewed federal attention; USFWS reevaluates grayling’s listing priority.
• 2006 – The Big Hole River Candidate Conservation Agreement with Assurances (CCAA) is launched, a voluntary conservation program with Big Hole watershed landowners.
• 2007 – USFWS issues a revised finding claiming the grayling does not qualify as a distinct population segment; grayling removed from candidate list.
• 2010 – USFWS reverses course, recognizes the Upper Missouri River fluvial Arctic grayling DPS, and again finds listing “warranted but precluded.” Grayling returns to candidate status.
• 2014 – After another review, USFWS finds listing “not warranted,” citing improvements from the CCAA. The decision is immediately litigated.
• 2018 – The Ninth Circuit vacates the 2014 decision and orders USFWS to reassess using stronger scientific evidence.
• 2020 – USFWS issues another “not warranted” finding, again relying heavily on the Big Hole CCAA and perceived habitat improvements.
• 2024 – A federal court vacates the 2020 decision, ruling that USFWS did not adequately analyze threats or population viability. USFWS is ordered to re-do listing determination.
• 2025 – New analyses, including the Hoylman (2025) report, are submitted to USFWS for incorporation into the current Species Status Assessment (SSA), which will inform the forthcoming court-ordered ESA listing determination.