So, you like to fish? You’re not alone. In 2024 (the most recent year with complete records), over 487,000 fishing licenses were sold in the state of Montana, including about 165,000 non-resident, 1-day licenses. This seems like a big number, especially when hoot-owl regulations close streams to fishing from 2 p.m. to sunrise daily and together with outright stream closures limit the number of places and hours you can fish in a day. This summer, 21 rivers in western Montana were under restrictions that limit fishing, and in Yellowstone National Park, the Madison, Firehole, and Gibbon rivers and their tributaries were completely closed to fishing by mid-July.
Hoot-owl restrictions and closures were first enforced in the early 2000s by Montana Fish, Wildlife and Parks, but they have become more frequent and on a greater number of rivers in Montana ever since. Why? Because the climate is getting warmer as a result of increased greenhouse gases in the atmosphere (largely from the combustion of fossil fuels). According to National Oceanic and Atmospheric Administration, average annual temperatures in Montana rose 2.5-3.0 degrees Fahrenheit between 1950 and 2024. At the same time, precipitation has decreased in winter and increased in spring. With warmer temperatures, there is less snow and more rain, the snow melts faster, spring runoff comes earlier, and summers are relatively dry.
When stream temperatures reach 73 degrees Fahrenheit for three consecutive days, hoot-owl restrictions are imposed. When angler pressure, warm water, and diminished stream flow act together complete closures occur, as happened for much of the Big Hole River this summer. At these higher stream temperatures, native trout become more vulnerable to disease, decreased levels of dissolved oxygen, and competition from nonnative species. Water temperature also directly effects fish growth. Generally, the rate at which fish grow increases with temperature up to a maximum, but once that temperature threshold is crossed, growth rates slow. Cold water in some small headwater streams is currently below the optimum temperature, and warming from climate change can spur fish growth. Unfortunately, in mainstem river habitats, summer water temperatures exceed the threshold, slowing fish growth and increasing stress. It’s these mainstem rivers, such as the Big Hole, Madison, and Jefferson rivers, where most fishing occurs and where competition from nonnative fish is greatest.
Declining streamflow during summer further complicates the problem. Shallow water reduces the number of stream pools and riffles where fish live and thus their abundance. An earlier and shorter spring runoff results in a longer period in summer when low stream flows are unfavorable for trout.
In contrast, large deep lakes in Montana are somewhat buffered from increasing air temperatures, and the area of a lake with optimal water temperatures for fish growth may actually increase as the climate warms. However, native Cutthroat and introduced Rainbow trout are spring spawners that reproduce in tributary streams. These spawning migrations are closely linked to the timing of snowmelt and runoff, and as the climate continues to warm, these trout will have to adapt to earlier peak flow, followed soon thereafter by lower flows and warmer stream temperatures. Studies have shown that average peak runoff in Yellowstone rivers is now 8 days earlier than in the 1950s, and summer stream flows have declined by 28 percent.
So, the bottom line is that rising air temperatures and changing precipitation patterns are currently reducing our opportunities to fish for prized trout. It seems to me that we need to act now to slow climate change so that in the decades ahead, our grandchildren can still enjoy some of the great fishing holes that we’ve known.
Bob Gresswell is a retired fish biologist from the US Geological Survey Northern Rocky Mountain Research Center. He has studied the ecology and management of Cutthroat trout in Yellowstone and the West for over 50 years.
By Bob Gresswell: August 26, 2025 – Bozeman, Mt
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