Native Yellowstone cutthroat trout Oncorhynchus virginalis bouvieri Bendire 1882 growth and survival in a headwater stream primarily driven by warming stream temperatures, with non-native brown trout Salmo trutta Linnaeus 1758, posing an additional t

Warming rivers and interactions with non-native species impact salmonid species globally. Understanding how hydroclimatic conditions synergistically and independently interact with non-native species is critical for effectively managing salmonids into the future. We used a 10-year mark-recapture dataset to assess how native Yellowstone cutthroat trout Oncorhynchus virginalis bouvieri Bendire 1882 (hereafter YCT) and non-native brown trout Salmo trutta Linnaeus 1758 growth rates and apparent survival were affected by hydroclimatic conditions and (for YCT) the presence of brown trout in a tributary. Growth (YCT) and survival (both species across size classes) were negatively related to warming stream temperatures. Brown trout growth was positively related to increasing daily streamflow variability (a proxy for streamflow), but this variable was not included in the top YCT growth model. Density dependent effects appeared to be nonexistent (growth) or weakly positive (survival). When sympatric with brown trout, YCT displayed worse survival than allopatric YCT across environmental conditions. Broadly, we found native and non-native trout respond to different hydroclimatic conditions that shift with changing climatic conditions; and brown trout represent an additional threat to YCT survival.