Fish index 

Add this one to the global warming binder. Last week, national anglers’ nonprofit Trout Unlimited released a report detailing a phenomenon circulated anecdotally among fisherman for several years now—that climate change is causing a decline in the health of mountain trout fisheries.

Trout Unlimited’s 35-page report—released July 23—details the impact of rising river water temperatures and falling flows across the Intermountain West in what State Director Bruce Farling calls the first comprehensive evaluation of the issue. The document addresses both the environmental aspects of changing habitat and the associated economic loss in sport fishing revenue.

“For us the global warming issue is personalized a little bit,” Farling says of the report. “Nobody has ever looked at all the data; it’s sporadic and a lot of it makes it hard to do the dot connecting. We looked at everything that was out there.”

Among eight Inter-mountain West rivers, the report ad-dresses two in Montana: the Bighorn and Beaverhead County’s legendary Big Hole—home to the last remaining native arctic grayling in the Lower 48. Trout Unlimited researchers relate the struggles of fish populations in these rivers to government stream closures and the loss of tourism dollars to Montana’s $300 million sport fishing
industry.

“We wanted to make the report more than something abstract,” Farling says. “We wanted to talk about real places that people have an affection for.”

According to hydrologist Chris Brick of the nonprofit Clark Fork Coalition, average stream flows have declined steadily since the middle of the last century while the recorded days with water temperatures exceeding 65 degrees continues to climb. The cause is a mix of reduced annual snow pack and air temperatures that have risen 1.8 degrees in Missoula since 1950.

Still, Tom France of the National Wildlife Federation says, “It’s often hard and its often overwhelming relating the science to what’s going on at home.”

At home, local scientists say the rising water temperatures are particularly hard on bull trout and westslope cutties. Though, warm water also aids the spread of whirling disease—a parasitic infection reportedly wreaking havoc on rainbow trout populations. Clark Fork Coalition data shows that brown trout have recently replaced rainbows as the dominant trout species in Missoula’s local blue-ribbon stream, Rock Creek.
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