Brook trout are the only species of trout native to the streams of the Great Smoky Mountains National Park (GSMNP) but are experiencing high death rates and population declines. These cold-water fish spawn in the fall and hatch in the late winter to early spring in response to water temperature cues – making them sensitive to increasing water temperatures. Yet, knowing where populations of brook trout are most vulnerable to climate change is challenging because climate stressors like changing water temperatures and stream flow patterns vary drastically from stream to stream, even those just short distances apart. 

Researchers supported by the Southeast CASC analyzed long-term datasets on temperature and stream flow to understand their impacts on the declining populations and increased mortality rates of brook trout. Their findings, published in the Journal of Agricultural, Biological, and Environmental Statistics, show that rainfall can counteract of the adverse effects of hot summers on trout populations. They also show that high winter stream flows, which can dislodge eggs from the safety of the streambed, reduce the number of newborn trout in many, but not all, streams. On the other hand, streams with cooler temperatures and consistent stream flow provide better conditions for trout survival and maturation, suggesting that these streams may be good climate refuges. 

Findings from this Southeast CASC-supported study can help identify vulnerable streams and those with the potential to be climate refuges for brook trout. Because neighboring streams may experience different climate stressors across small areas in the GSMNP, this work could be used to create more targeted management approaches that support the important biological and recreational services the fish provides. Additionally, authors of the study note that their analytical framework can be extended beyond brook trout to help develop adaptive management strategies in other species and ecosystems. 

This work was supported by the Southeast Climate Adaptation Science Center Project titled “Brook Trout Population Responses to Climate Variation Across the Southeast USA.”