The interactive effects of stream temperature, stream size, and non-native species on Yellowstone cutthroat trout

Climate change and non-native species are considered two of the biggest threats to native salmonids in North America. We evaluated how non-native salmonids and stream temperature and discharge were associated with Yellowstone cutthroat trout (Oncorhynchus clarkii bouvieri) distribution, abundance, and body size to gain a more complete understanding of the existing threats to native populations. Allopatric Yellowstone cutthroat trout were distributed across a wide range of average August temperatures (3.2 to 17.7 degrees C), but occurrence significantly declined at colder temperatures (<10 degrees C) with increasing numbers of non-natives. At warmer temperatures, occurrence remained high, despite sympatry with non-natives. Yellowstone cutthroat trout relative abundance was significantly reduced with increasing abundance of non-natives, with the greatest impacts at colder temperatures. Body sizes of large Yellowstone cutthroat trout (90th percentile) significantly increased with warming temperatures and larger stream size, highlighting the importance of access to these more productive stream segments. Considering multiple population-level attributes demonstrates the complexities of how native salmonids (such as Yellowstone cutthroat trout) are likely to be affected by shifting climates.

Automated summary

This research highlights the impacts of non-native species, stream temperature, and discharge on the distribution, abundance, and body size of Yellowstone cutthroat trout. It shows that warmer temperatures and larger stream sizes are beneficial for large Yellowstone cutthroat trout, while colder temperatures and higher abundance of non-natives negatively affect their relative abundance. Multiple population-level attributes need to be considered to understand how native salmonids like Yellowstone cutthroat trout are affected by changing climates.