Climate Change Threatens Native Trout Diversity

BOZEMAN, Mont. – Scientists have discovered that the diversity of a threatened native trout species will likely decrease due to future climate change. 

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Researchers have found that in native bull trout, genetic diversity – critical for species to adapt to a warming world – is already lowest where stream temperatures are warmest and winter flooding is highest. These trends are predicted to continue into the future, suggesting that this imperiled species is more susceptible to climate change than previously thought. 

“Genetic diversity is extremely depressed where future climatic conditions may be most challenging for bull trout,” said U.S. Geological Survey scientist Ryan Kovach, the lead author of the report. “Together, these results highlight that bull trout may have little resiliency in a warming world.”

The study, published in Global Change Biology, combined estimates of stream habitat conditions, current and future stream temperatures and flows, and estimates of genetic diversity patterns in 130 bull trout populations from 24 watersheds across the Columbia River Basin. The bull trout was listed as "threatened" under the U.S. Endangered Species Act in 1998.

Researchers with the USGS, University of Montana and U.S. Fish and Wildlife Service examined whether bull trout genetic diversity was related to climate vulnerability at the watershed scale, which was determined on the basis of current and future predictions of stream temperature and flow and existing habitat conditions.  

“Although genetic diversity is literally the fundamental building block for all life, it is almost completely ignored in the context of climate change,” said Kovach. “Our research shows that genetic diversity in a rare trout species is strongly related to climate and may provide little buffering in the future. By ignoring these patterns we may be under-estimating the potential impacts of climate change, a problematic situation for species like bull trout that are already at risk of extinction in the United States.”

The study found that in bull trout populations across the Columbia River Basin genetic diversity was greatest in the most upstream headwater areas, and decreased in populations downstream. Genetic diversity was also greater in bull trout populations living in larger and more complex areas of habitat, but was lower in populations inhabiting low-complexity, warm streams, with frequent winter flooding. 

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“Over the next century, stream habitats will warm and stream flows will become more variable across the Columbia River Basin. However, our study shows that fish populations that will need to adapt the most to these changes may have the lowest adaptive potential because they have the lowest amounts of genetic diversity,” said co-author and USGS scientist Clint Muhlfeld. “Therefore, managers can increase resiliency and adaptive potential in vulnerable populations by reducing existing stressors, such as restoring and reconnecting cold, clean and complex habitats, and reducing impacts of invasive species.” 

The article is titled “Genetic diversity is related to climatic variation and vulnerability in threatened bull trout” and can be viewed at the following website.  

This study was supported by the USGS USGS National Climate Change and Wildlife Science Center, the Great Northern Landscape Conservation Cooperative and the Department of Interior Northwest Climate Science Center.

More information about aquatic species vulnerability to climate change can be found on the USGS Northern Rocky Mountain Science Center website.