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Study: Changing climate could cut Western trout habitat in half

Trout Unlimited Press Release
BOISE, Idaho — A new study shows a changing climate could reduce suitable trout habitat in the western U.S. by about 50 percent over the next 70 years, with some trout species experiencing greater declines than others. The results were reported by a team of 11 scientists from Trout Unlimited, the U.S. Forest Service Rocky Mountain Research Station, Colorado State University, the U.S. Geological Survey and the University of Washington Climate Impacts Group.

The study, published Aug. 15 in the peer-reviewed science journal Proceedings of the National Academy of Sciences, predicts native cutthroat throughout the West could decline by as much as 58 percent, while introduced brook trout could decline by as much as 77 percent. Rainbow and brown trout populations, according to the study, would also decline by an estimated 35 percent and 48 percent respectively.

The study notes that the decline of cutthroat trout is "of particular significance, " because cutthroats are the only trout native to much of the West and a keystone species in the Rocky Mountain ecosystem.

"The study advances our understanding of climate change impacts by looking beyond temperature increases to the role of flooding and interactions between species, " said TU’s Dr. Seth Wenger, the paper’s lead author. "The study also is notable in scope, using data from nearly 10,000 sites throughout the western United States. "

Wenger was quick to point out that, while the predictions are indeed dire, there is hope. By restoring and reconnecting coldwater drainages and by protecting existing healthy habitat largely located on public lands in the West, some of the decline in trout populations can likely be avoided.

"Essentially, Trout Unlimited is already protecting remaining strongholds and restoring degraded habitat — exactly the kind of things that need to be done to reduce the impact of a changing climate on coldwater fisheries in the West, " Wenger said.

"This report is a wake-up call, " said Chris Wood, the president and CEO of Trout Unlimited. "The good news is that we’re already working to protect high-quality trout habitat, such as backcountry roadless areas on national forests. We’re reconnecting tributaries to mainstem rivers, and we’re restoring degraded habitat. It is imperative that we accelerate the scope and the pace of that work if we are to have healthy trout populations and the irreplaceable fishing opportunities they provide through this century."

Wenger and his fellow researchers used an "ensemble " of climate models to arrive at the study’s findings. Some models predicted more warming than others, but under even the most "optimistic " model, cutthroat trout populations in the West could decline by 33 percent. Scientists note that cutthroat trout populations are already in trouble — some subspecies have been removed from 90 percent of their historic native range and are listed under the Endangered Species Act. Declines from a changing climate would impact native cutthroat trout beyond the impacts they’ve already suffered.

"This study validates the work TU is doing in the West and all across the country to protect, reconnect, restore, and sustain trout habitat, " Wood continued. It also reinforces the danger in congressional proposals that would remove protection from backcountry roadless areas and cut funding for state and federal natural resource agencies."

The study can be read in its entirety here, or at Proceedings of the National Academy of Sciences website when it publishes Aug. 15.

The research was funded by the National Fish and Wildlife Foundation, the U.S. Geological Survey and the U.S. Forest Service Rocky Mountain Research Station.

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