Study says high mountain streams serve as ‘climate refuge’

There’s hope for coldwater fish in the West, especially if resource managers are able to plan and implement conservation measures

CDOW Aquatic biologist Jon Ewert holds a rainbow trout for measurement while sampling fish populations in the Blue River in Silverthorne, Colorado.
CDOW Aquatic biologist Jon Ewert holds a rainbow trout for measurement while sampling fish populations in the Blue River in Silverthorne, Colorado. @bberwyn photo.

Staff Report

Global warming is hitting the high mountain world especially hard, with records from recent decades showing temperatures above 13,000 feet increasing 75 percent faster than at lower elevations in some regions. But for a while at least, the high country may end up being a last-ditch climate refuge for many species, including cold-water fish.

A recent study suggests that water temperatures in mountain streams aren’t going up as fast as previously projected. That means there’s time to survey ecological communities and plan conservation strategies, according to a new study published in the Proceedings of the National Academy of Sciences.

“The great irony is that the cold headwater streams that were believed to be most vulnerable to climate change appear to be the least vulnerable,” said Dr. Daniel Isaak, lead author on the study with the U.S. Forest Service, explaining that the research team based its conclusions on a careful analysis of existing data.

The study, including scientists from several agencies and universities, drew information from huge stream-temperature and biological databases contributed by over 100 agencies and a USGS-run regional climate model to describe warming trends throughout 222,000 kilometers (138,000 miles) of streams in the northwestern United States.

During the past 40 years, stream temperatures warmed by about 0.18 degrees Fahrenheit per decade, shifting habitat upstream by about 300-500 meters per decade in headwater mountain streams where many sensitive cold-water species currently live. There’s no question that global warming is taking a toll on habitat, but apparently at a much slower rate than projected.

The results of this study indicate that many populations of cold-water species will continue to persist this century and mountain landscapes will play an increasingly important role in that preservation.

 

“One of the great complexities of restoring trout and salmon under a rapidly changing climate is understanding how this change plays out across the landscape,” said said Dr. Jack Williams, senior scientist for Trout Unlimited. “Dr. Isaak and his colleagues show that many mountain streams may be more resistant to temperature change than our models suggest and that is very good news. This provides us more time to effect the changes we need for long-term persistence of these populations,” Williams said.

The study, entitled “Slow climate velocities of mountain streams portends their role as refugia for cold-water biodiversity” was conducted by Daniel Isaak, lead author from the U.S. Forest Service Rocky Mountain Research Station; Michael Young, Charles Luce, Dona Horan, Matt Groce and David Nagel of the U.S. Forest Service Rocky Mountain Research Station; Steven Hostetler, U.S. Geological Survey; Seth Wenger, University of Georgia; Erin Peterson, Queensland University of Technology; and Jay Ver Hoef, U.S. NOAA Fisheries, Alaska Fisheries Science Center. Additional funding for this research was provided by the U.S. Fish and Wildlife Service Great Northern and North Pacific Landscape Conservation Cooperatives.

States covered by this study are Idaho, Oregon, Washington, western Montana, as well as small portions of western Wyoming, northern Nevada, northern Utah and northern California.

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