Climate Change Helping Hybridization between Native, Invasive Trout Species: USGS Study

Climate changes have resulted in the rapid cross-breeding of native and invasive species of trout, a new study based on a U.S. Geological Survey shows.

Researchers at the USGS along with colleagues at the University of Montana and Montana Fish, Wildlife & Parks found that change in temperature has accelerated hybridization between native westslope cutthroat trout and introduced rainbow trout.

Experts have predicted that warmer temperatures will help invasive fish grow and form hybrids with native fish. The study is published in the journal Nature Climate Change

Both westslope cutthroat and rainbow trout spawn in spring and can produce fertile inbred offspring. Sustained cross-breeding between two species leads to loss of genetic diversity in the ecosystem.

"Climatic changes are threatening highly prized native trout as introduced rainbow trout continue to expand their range and hybridize with native populations through climate-induced 'windows of opportunity,' putting many populations and species at greater risk than previously thought," said  project leader and USGS scientist Clint Muhlfeld, according to a news release. "The study illustrates that protecting genetic integrity and diversity of native species will be incredibly challenging when species are threatened with climate-induced invasive hybridization."

Rainbow trout can tolerate warmer water along with lower spring flows. For larger part of the last century, these trout species were found only in downstream Flathead River population. However, warmer temperatures have helped these fish swim upstream and mate with native fish, nbcnews reported.

The new study looked at data from 30 years and found that cutthroat trout have seen a reduction in their population. Currently, just ten percent of the cutthroat trout population are genetically pure.

"The evolutionary consequences of climate change are one of our greatest areas of uncertainty because empirical data addressing this issue are extraordinarily rare; this study is a tremendous step forward in our understanding of how climate change can influence evolutionary process and ultimately species biodiversity," said Ryan Kovach, a University of Montana study co-author.

The study was funded by the Great Northern Landscape Conservation Cooperative, the Interior Department's Northwest Climate Science Center and others.