Hybrid Trout Threaten Montana's Native Cutthroats Climate change in the West is luring rainbow trout to higher elevations, where the fish are mating with native cutthroats, genetic evidence shows. Biologists and anglers worry cutthroats could vanish.

Hybrid Trout Threaten Montana's Native Cutthroats

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Many parts of the US have been getting warmer over the past several decades and have also been experiencing persistent drought. Wildlife often can't adjust. NPR's Christopher Joyce reports on new evidence that a changing climate maybe threatening one of the American West most highly prized fish - the cutthroat trout.


CHRISTOPHER JOYCE, BYLINE: If you wade into one of the tiny streams of the Shields Basin in Montana, you might see a two-inch fish wriggling out from under a rock. These cold mountain streams are home to young cutthroat trout. Last year I was waiting in one of the streams with biologist Brad Shepard from the Wildlife Conservation Society. He was looking for invaders.

BRAD SHEPARD: What we are doing is we're looking at the invasion front of non-native fish as they are moving up, as the climate is warming.

JOYCE: The non-native fish are rainbow trout. They were introduced in the West decades ago to give anglers more fish to catch. The rainbows mostly stayed well down in the valleys - the mountain water was too cold. But over the past few decades, stream flow at higher elevations is down and water temperature is up. These conditions favor rainbow trout, so rainbows are moving upstream. When they meet the cutthroat, they mate and create a hybrid - essentially a new kind of trout.

SHEPARD: And it is irreversible. Hybrids produce hybrids.

JOYCE: Clint Muhlfeld is a biologist with the U.S. Geological Survey. He says there are still plenty of cutthroats, but they are all in danger of becoming hybrids. Now you might think, so what? A trout is a trout by any other name. But trout fishing brings in tens of millions of dollars just in Montana, and lots of anglers want to catch native cutthroat trout. More important, biologist like Muhlfeld worry that these hybrids might die out too, leaving fewer fish overall.

CLINT MUHLFELD: Well, we started studying this, we were first finding all these hybrid trout across all these water bodies and wondering what is hybridization do to their overall performance?

JOYCE: Now Muhlfeld and his colleagues have done the genetic research to answer that question. And in fact these hybrid trout don't do well at all.

MUHLFELD: The hybrid offspring have greatly reduced fitness. Their ability to produce offspring and have those offspring survive.

JOYCE: Muhlfeld says a change in climate triggered this phenomenon.

MUHLFELD: So essentially, hybridization was a time-bomb, waiting to go off under the right environmental conditions.

JOYCE: The genetic research appears in the journal Nature Climate Change. Christopher Joyce, NPR News.


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