UM Study Links Warmer Weather With Decrease in Cutthroat Genetic Purity, May Decrease Overall Trout Levels

A new article published in Nature Climate Change by researchers from the University of Montana shows a link between warmer temperatures and the interbreeding of native Westslope cutthroat trout with non-native rainbow trout. UM Division of Biological Sciences Professor Clint Muhlfeld says that hot dry temperatures in the early 2000s set off a time bomb of hybridization.

"What we see in the Flathead is that, despite millions and millions of rainbows being introduced over the last century, we only saw hybridization levels in large amounts in one source population. But over a 30 year period of rapid warming, we saw hybridization expand into the system irreversibly corrupting those native gene pools which have evolved over thousands, and thousands of years."

Muhlfeld and his team compared modern genetic data of trout with genetic data gathered in the 70s and 80s to reach the conclusion that slower stream flows and warmer stream temperatures were pushing the two trout species to hybridize at a quickening pace.

Muhlfeld says the hybridized trout have lower survival rates than Westslope cutthroat trout and that, if warming trends continue, it may lead to a decrease in the overall number of trout in Montanan’s rivers.