A warming climate has accelerated the growth of a non-native trout population in a northwest river system to the detriment of the area's westslope cutthroat trout, says a new research study.
During the late 1800s to 1969, some 20 million rainbow trout were stocked in waters that flow through Montana and southern British Columbia, and they have been mating with the river system's native cutthroat, NBC News reported.
The hybridization between the two trout varieties could eventually render the pure native fish extinct, especially since a warming climate has spurred the rainbow population to greater growth.
"This is the first example we are aware of that has shown how invasive hybridization has probably spread due to climate warming," Clint Muhlfeld, lead study author and a research ecologist with the U.S. Geological Survey in West Glacier, Mont., told NBC News.
Because rainbows thrive in warmer waters, the non-native trout were generally confined to parts of the Flathead River system that are protected from cold waters and spring flooding, restricting the chances for hybridization with cutthroats.
But Muhlfeld points to a drought in the early 2000s that resulted in the warmer waters and lower spring flows preferred by rainbows as the "right environmental conditions" to encourage crossover between the two types of trout.
Conservation groups have been working to plug streams with dams in an attempt to stop rainbow trout from spreading even more through the river system.
As he details in the study published in Nature Climate Change, Muhlfeld says a growing rainbow population means that "over time you're going to lose the native cutthroat trout. The writing is on the wall."
According to Muhlfeld's research, hybridized fish that have rainbow accounting for even 20 percent of their DNA are only half as fit as the original native fish with pure DNA.
"This has important consequences," Muhlfeld told NBC News. "If our native fish are mostly hybridized and their fitness is lower, then their potential to be resilient and adapt in the face of climate change is going to be reduced."
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