Wyoming’s legendary trout fishing, especially for cutthroats, draws people from all over. Cutthroats need cold water, so there’s concern over a new study that says water temperatures are rising.
An analysis recently published by the University of Wyoming Extension office zeros in on the Snake River headwaters in Teton County.
The analysis considers possible future scenarios driven by current trends. A “shrinking snowpack” scenario could lead to earlier spring runoff, lower water levels, and higher water temperatures during the summer, according to researchers.
That could threaten the viability of prized native trout, particularly cutthroats, researchers warm.
Wyoming fishing guide Chris Hayes said he’s already seeing a running trend of warmer water temperatures along the Snake River, Green River and other watersheds.
In terms of sensitivity to water temperature, Hayes said he thinks that cutthroat trout are the most affected, followed by rainbow trout, brook trout, and brown trout.
The trend of shallower, warmer waterways was especially apparent this year, Hayes told Cowboy State Daily.
“It’s been a really rough year,” he said. "At the beginning of July, we were looking at water levels (on the Green River) that were normally what we’d see at the end of July or the beginning of August."
Warmer Water, Algae Rob Oxygen
The common wisdom is that warmer water makes fish lethargic. Hayes said that’s because warmer water tends to have less oxygen in it.
Shallow water also allows more sunlight to reach the riverbed, spurring the growth of more plants and algae.
Initially, that might seem like a good thing, because plants put oxygen back into the water, at least during daylight.
But after dark, the plants’ cycle reverses and they start taking oxygen out of the water, Hayes said. After absorbing sunlight all day, the water will retain heat long after sunset.
“Fish get hit with a double whammy” of the plants and the lingering heat both lowering oxygen levels, he said.
Different Species, Different Heat Tolerances
Hayes said he’s not sure why cutthroat are the trout species most sensitive to heat. It’s likely because they’re native to places such as the upper Snake River and upper Yellowstone River, where waters are naturally colder.
Snake River cutthroats and Yellowstone cutthroats have a big appeal for out-of-state clients, he said.
“There’s certainly an appeal for some people to catching those fish in their native waters,” he said.
Brown trout are originally from Europe, and those in Wyoming are most likely from genetic lines going back to Germany and Scotland, Hayes said.
Brook trout originate on the East Coast, he added.
There’s also some disagreement over whether Colorado River cutthroat trout are native to the Green River basin, Hayes said.
The Wyoming Game and Fish Department argues that those fish might have at some point migrated up from their core habitat in Colorado, because the Green River is a tributary of the Colorado River, he said.
However, Hayes doesn’t think that’s possible. The stretch of the Colorado River that flows through Utah is too hot and silty for Colorado cutthroat trout to have made the journey, he said. So, they must have been transplanted into the Green River at some point.
Magic Numbers
While there have been some wet, cool years over the past decade, the general trend has been hotter and drier, Hayes said.
Anglers and guides do what they can to mitigate the situation, he said. People who use spin-casting lures or bait tend to keep fishing when it gets warm because they plan on keeping the fish for food.
Most fly-rod anglers do catch-and-release, he said. So, they’re mindful of stressing fish out by catching them when the water is warm.
He said the “cutoff point” for catch-and-release fishing is generally sustained water temperatures of 70 degrees.
“Some people are going farther than that, 68 degrees is the cutoff number,” Hayes added.
So far in Wyoming, that’s done voluntarily, Hayes said. Other states and the national parks have implemented “hoot owl” fishing hours, meaning that fishing isn’t allowed during peak heat times.
Fishing Under Hoot Owl Regulations
Hoot owl regulations are in force on some rivers in Montana, fishing guide Kyle Rausch told Cowboy State Daily.
In most cases, the restrictions are based on prolonged water temperatures of 71 degrees or higher, said Rausch, who is the owner and operator of Missoula-based R.R. 406 Fly Fishing guide service.
When hoot owl is in effect, fishing isn’t allowed from 2 p.m. until midnight, he said. The idea is that by midnight, the water has had enough time to cool off.
Also noting how sensitive cutthroat trout are to heat, Rausch said the hoot owl restrictions go into effect once the water hits 65 degrees in on the upper Bitterroot River in Montana. That’s a first-class cutthroat fishery.
Rausch agreed that the lower water content in warm water makes things tough on trout.
When a big trout fights for a long time before being reeled in, only to be put back into warm water, “it’s like running a 400-meter sprint, and then having to recover with only half the normal oxygen,” he said.
Mark Heinz can be reached at mark@cowboystatedaily.com.
