Study: Climate change threatens cutthroat trout habitat

Cutthroat trout usually have bright red slash marks on their throats. Great Falls Tribune File Photo

cutthroat trout
A study, published Monday in Proceedings of the National Academy of Sciences, by fisheries researchers concludes that climate change might cut the West's trout habitat in half over the next 70 years.

The cutthroat trout (Oncorhynchus clarkii) is a species of freshwater fish in the salmon family of order Salmoniformes. It is one of the many fish species colloquially known as trout. The common name "cutthroat" refers to the distinctive red coloration on the underside of the lower jaw.

Cutthroat (right) are typically prized as a sportfish, particularly by fly anglers, as their propensity to inhabit remote waters and diminutive streams appeals to the sense of adventure present in many outdoor enthusiasts. In addition, their tendency to exhibit significant activity and resistance to anglers in conjunction with this species' affinity for terrestrial or mature insects serves to bull troutincrease popularity of the cutthroat as a angler's quarry. Finally, the cutthroat participates in a unique predator-prey relationship with the bull trout (left) that is key to ecosystem integrity across much of its natural range.

Several native subspecies of cutthroat are currently listed as threatened, generally due to loss of habitat and introduction of non-native species. Native cutthroat species are found along the Pacific Northwest coast, in the Cascade Range, the Great Basin, and throughout the Rocky Mountains.

Trout Unlimited's Seth Wenger and U.S. Forest Service biologist Dan Isaak were among 11 researchers who found, among other things, that cutthroat habitat could dwindle between 33 percent and 58 percent.

That's after the range of cutthroat habitat (left: range @USGS) has already shrunk by more than 85 percent due to competition from non-native species like rainbow trout and brook trout. Two subspecies have already gone extinct.

Isaak said he knows there will be skeptics but defends the foundations of the research. The climate predictions are based on 10 of the 20 climate model credit CESMclimate models (right: @CESM) 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.

trout eggsThe study concludes warmer winters are causing more winter floods that wash away the gravel that holds brook and brown trout eggs (left). And changing flows will give rainbow trout an advantage over native cutthroat trout, allowing the invaders to crowd out the natives.

Wenger said the paper was based on data collected from nearly 10,000 fish surveys conducted in the western half of Montana, as well as the western parts of Colorado and Wyoming, eastern and troutnorthern Idaho, and Utah. The data was used to build statistical models that forecast the decline in total suitable habitat.

Fortunately, trout populations don't yet show impacts of climate change, the authors said. And Wenger said the numbers beyond 2050 are uncertain, leaving the potential scale of the impact on cutthroats open to interpretation.

But Wenger said the most dire climate models show temperatures in Idaho rising an average of 9 degrees in 70 years.

"The overall picture is fairly negative for trout," Wenger. "The sort-of good news is that there is still some uncertainty of how much warming we will see. But even the best-case scenario isn't great."
UFS model mountain streamThe scientists said human intervention could help. Stepping up measures to reconnect cooler trout waters and restore stream side trees and vegetation would keep streams cooler (left: UFS model forest). There could also be changes to the climate beyond man's control, including the eruption of a volcano whose ash cloud serves to cool things for years to come.


Great Falls Tribune,"Study: Climate change threatens cutthroat trout habitat", accessed August 18, 2011

Helena Independent Record, "Idaho study: Trout face climate change troubles", accessed August 18, 2011


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