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Tough But Sensitive: How Climate Change Threatens Bull Trout

Bull trout
flickr/USFWS Headquarters
Bull trout

In the beginning, the idea of global warming was easy for me to ignore. Of course I found the footage of floating polar bears distressing, but the ice caps seemed far away, and scientists seemed even farther from any real answers. Instead, I distracted myself with fantasies of extended summer vacations and longer-lasting tans. Although I admit to subscribing to some serious misinformation, I have come to realize that climate change threatens far more than just the fierce and fuzzy white denizens of the Arctic. In particular, I began noticing newspaper and journal articles that warned of the effects of climate change on one of my favorite Montana native species, the bull trout. I learned that even slight increases in temperatures in the Pacific Northwest will warm waters enough to make them uninhabitable for bull trout. Without this fish, the prospect of longer summers and milder winters lost its appeal.

Bull trout are one of the world’s most sensitive cold-water fish species and need different temperatures throughout their lifetime in order to survive and successfully reproduce. They wait till fall to spawn, after water temperatures drop below 48 degrees Fahrenheit. The fish then migrate long distances, sometimes over 100 miles, to lay their eggs in the cold headwaters of mountain streams. In order for bull trout eggs to properly develop, the water must stay in the 30s or low 40s during incubation. It can take the eggs up to eight months to hatch, longer than any other trout or salmon species.

The U.S.D.A. Forest Service recognized the sensitivity of bull trout and used predictions made by the Intergovernmental Panel on Climate Change to determine the effects of rising temperatures on bull trout habitat. Climate change experts predict a minimum average warming of 2 degrees Fahrenheit in the next 50 years and an increase of over 10 degrees in the next 100 years. And while a few degrees seem minimal to us, it will have devastating effects on bull trout. For every degree the temperature rises, bull trout become restricted to higher elevations where the water is cooler.

The result is a conservationist’s nightmare: dramatic loss in genetic diversity, fragmentation and isolation of populations, and the loss of an important predator from native ecosystems. The studies published by the Forest Service in 2007 predict enormous losses in bull trout habitat, up to 90 percent over the next 100 years.

As temperatures continue to rise, some of the last suitable habitat for bull trout will be found right here in western and southwest Montana. Because of the cold temperatures of our high mountain streams, we have an edge in preserving this fish species. Bull trout need the “four c’s” to maintain healthy populations: Clean and Cold water, Connected and Complex habitats. Preserving bull trout habitat in Montana means keeping waterways free of pollution, preventing development that causes erosion along our rivers, and ensuring that fish can migrate past dams.

Journalist and outdoorsman Greg Tollefson wrote of a fishing trip in one of western Montana’s many mountain streams. After fooling a small trout with a fly, he watches the shadowy missile of a bull trout slice from the depths and clamp its jaws around his already-hooked fish. The fish-thief tears back down to the clouded depths as line strips off Tollefson’s reel. Readers are assured that this would only happen in “Bull Trout Country,” where a game of tug-of-war with this wild and aggressive fish leaves the lucky angler with an experience unrivaled by any other freshwater fish species in the Northwest. Fortunately for us, this may be a marvel we can enjoy in Montana for generations to come.

"Field Notes" is produced by the Montana Natural History Center.

(Broadcast: "Fieldnotes," 10/27/15. Listen on air or online Sundays at 12:55 p.m., Tuesdays at 4:54 p.m., and Fridays at 4:54 p.m., or via podcast.)

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