Study finds Idaho trout face climate trouble

Story by Rocky Barker
The Idaho Statesman
August 17, 2011
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When Seth Wenger and Dan Isaak release a scientific paper that predicts hard times for the West's trout, they know a lot of people are skeptical.

"Fundamentally, skepticism is a good thing in science," said Wenger, a fisheries researcher with Trout Unlimited in Boise.

Both Wenger and Isaak, a fisheries biologist at the U.S. Forest Service's Rocky Mountain Research Station in Boise, were a part of a team of 11 scientists who said trout habitat could drop by 50 percent over the next 70 years because of a warming world. The paper, published Monday in the peer-reviewed science journal Proceedings of the National Academy of Sciences, predicts native cutthroat habitat could decline by 58 percent.

The two men, who have devoted their lives to scientific research, say they depend on the scientific method and peer review to judge the quality of the research that underscores their findings. The climate predictions are based on 10 of the 20 climate models developed independently worldwide that all show the world is getting warmer.

"The climate models have been right for 30 years and they are getting better all the time," Isaak said.

The data these men have collected in the watersheds of the West shows the same trends, they said. And warmer water isn't the only problem.

The research also shows that warmer winters are causing more winter floods that wash away the gravel that holds brook and brown trout eggs.

The changing spring and summer flows give rainbow trout an advantage over native cutthroat trout in the rivers they share, allowing the invaders to crowd out the natives. And the forecast for the future is more unnerving to these researchers and anglers than even they want to believe.

The most dire climate models show temperatures in Idaho rising an average of 9 degrees in 70 years, Wenger said. "That would make Boise pretty unpleasant," he said. "None of us want to believe that."

But Wenger is a scientist. He may hope the models that predict only a 4- to 5-degree rise over 70 years are more accurate, but he has to use the science that is available.

"I have to set aside my feelings and use the best data," he said.

The best data says it's going to get warmer, but there remains a lot of uncertainty in the numbers, especially past 2050, Wenger said. So there is a range of possible impacts on cutthroats. The scientists forecast reductions in habitat ranging from 33 percent to 58 percent.

But these findings are only predictions.

"We are not yet seeing the trend in the trout populations themselves," Wenger said.

And all of these predictions are based on current conservation practices. If the nation and the region were to step up measures to reconnect cooler trout waters and restore streamside trees and vegetation that keep streams cool, then the future could be brighter.

But what if all the climate models are wrong?

"There just is not a lot of data supporting the alternative view," Wenger said.

There are natural events that could change the trend, Isaak said.

A large volcano eruption could cool global temperatures for years or even decades.

Or an asteroid could hit and send millions of tons of material into the atmosphere for decades.

Beyond 2050, a dramatic reduction in greenhouse gases from a quick transition away from fossil-fueling burning could slow the warming, but even that is uncertain, Wenger said.

If the natural or man-made actions don't take place, Wenger's team of 11 scientists predict, rainbow trout habitat may drop by 35 percent and brown trout by 48 percent. Surprisingly, brook trout, introduced from eastern streams, could decline by as much as 77 percent.

That actually could help bull trout, listed as a threatened species, Isaak said.

"It may prove that bull trout tend to be more resilient," he said.

To contact Rocky Barker call 377-6484.

Rocky Barker

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