Wild About Utah

One of the lesser-known natural, and underappreciated, areas in our state is found 32 miles south of Vernal in eastern Utah: the Ouray National Wildlife Refuge. My wife and I visited last July, hoping to see bird species we don’t find in other parts of the state. We enjoyed the birding, but what made the visit most memorable to me wasn’t birds, but fish.

The refuge lies along the Green River, the largest tributary of the Colorado. If you drive far enough down the main refuge road, you’ll come to the Ouray National Fish Hatchery, dedicated to protecting three of the rarest fishes in North America: the bonytail, the humpback chub, and the razorback sucker.

All three of these species are confined to the Colorado River watershed, and all are on the federal Threatened and Endangered Species list. They’re desert fish, used to warm water. In fact, I learned that one reason why populations of these fish declined in the 1960s was that construction of the Flaming Gorge Dam upstream had made the Green River much cooler, as the water flowing through the dam was drawn from the coldest depths of the reservoir. That was great for trout, turning a 30-mile stretch of the Green into a world-renowned fishery. But it wasn’t so good for desert-adapted fish.

Learning this made me curious. The Ouray refuge is in the Uinta Basin. and it gets cold in the Basin in the winter. So, if cold water is bad for them, how have the bonytail, humpback chub, and razorback sucker survived there for thousands of years?

To answer that, it helps to understand the terms that anglers and fisheries biologists use. They refer to cold water species, like trout, kokanee, and whitefish, and warm water species like bass, perch, and catfish. The rare Green River species are warm water fish. But those labels aren’t about what temperatures the fish can survive, they’re about temperatures they experience when they thrive – during the warmer half of the year.

All fish are cold-blooded. More specifically, they’re ectothermic, getting their body heat from their environment, and poikilothermic, having a body temperature that fluctuates with the temperature of the waters where they live. To survive in winter, they go into a low-energy state called “torpor.” Their heart rate drops, their metabolism slows to a crawl, and their need for food is basically nonexistent. It’s like hibernation, except it happens in the deeper, slower water of a river instead of a cave or burrow.

That’s an important adaptation for the Colorado River fishes. Bonytail and humpback chub feed on insects, crustaceans, seeds and plants, occasionally small fish, all of which are much harder to find in the winter. Razorback suckers eat insects, plankton, and decaying plant matter – also less available in the winter months.

Now that we’re heading into springtime, when the weather gets warmer and the river along with it, both the fish and their prey are becoming active again.

Temperature is no longer a big threat to survival of these species. Flaming Gorge Dam has been re-engineered so that warmer water is drawn through its turbines. Also, flows through the dam are altered during spawning season to increase survival of fish larvae. The Ouray hatchery raises young fish to boost their population. The biggest threats to these species are habitat destruction and competition from non-native fishes. Those are challenges that are much harder to address. But it’s good to know there are biologists helping to recover the rare native fishes of the Green and Colorado Rivers.

I’m Mark Brunson, and I’m wild about Utah’s aquatic species and habitats.

Credits:

Images: Johnson Bottoms, Courtesy US FWS, John Orlanda, Photographer
Razerback Sucker, Courtesy US FWS, Sam Stuckel, Photographer
Bonytail Chub, Humpback Chub, Courtesy US FWS
Featured Audio: J. Chase and K.W. Baldwin as well as Friend Weller, https://upr.org/
Text: Mark Brunson, https://www.usu.edu/experts/profile/mark-brunson/
Additional Reading: Mark Brunson, https://www.usu.edu/experts/profile/mark-brunson/ & Lyle Bingham, Bridgerland Audubon Society

Additional Reading

Mark Brunson’s archive: https://wildaboututah.org/?s=brunson

Upper Colorado River Endangered Fish Recovery Program, U.S. Fish and Wildlife Service, https://www.fws.gov/office/upper-colorado-river-endangered-fish-recovery-program/species

Ouray National Wildlife Refuge, U.S. Fish and Wildlife Service, https://www.fws.gov/refuge/ouray

Ouray National Fish Hatchery, U.S. Fish and Wildlife Service, https://www.fws.gov/fish-hatchery/ouray

Fish, Dinosaur National Park, National Park Service, https://www.nps.gov/dino/learn/nature/fish.htm

Endangered Species Day: A look at how DWR, other agencies are helping razorback suckers in Utah, News, Utah Division of Wildlife Resources, May 14, 2020. https://wildlife.utah.gov/news/utah-wildlife-news/919-endangered-species-day-helping-razorback-suckers.html

Where do fish go when it freezes outside?, National Oceanic and Atmospheric Administration (NOAA), https://oceanservice.noaa.gov/facts/fish-freeze.html