A study authored by the U.S. Forest Service and other organizations including Trout Unlimited finds that global warming is expected to reduce the distribution of trout in the western U.S. because warmer streams will be less suitable for their growth and survival. Native trout will decline primarily in response to water temperature but also to interactions with nonnative species. Additionally, some nonnative species will also decline as winter flooding become more frequent.
The study Flow Regime, Temperature, and Biotic Interactions Drive Differential Declines of Trout Species under Climate Change includes forecasts of native and non-native trout distribution and survival over 70 years. Along with rising water temperatures, the authors looked at the vulnerability of eggs and young trout to predicted increases in seasonal flooding.
Some of the study’s findings include:
- Cutthroat trout and brook trout are most affected by warmer water
- Brown trout exhibit a greater thermal tolerance
- High winter flows will threaten fall-spawning brown trout and brook trout but are likely to benefit rainbow trout, which have a genetic history of surviving under similar conditions in their native range
The study, published in the journal Proceedings of the National Academy of Sciences, suggests that land management agencies take into consideration the complex interaction of climatic change to develop targeted actions supporting different species in different locations.
Strategic actions, the study emphasizes, can enhance the sustainability of trout populations despite the uncertainty in climate change predictions. Under any scenario, protecting and restoring high-quality trout habitat is fundamental to ensuring a vibrant trout presence in the American West.