Spatiotemporal Patterns of Smallmouth Bass (Micropterus dolomieu) Reproduction and Recruitment at Its Upstream Invasion Front in a Pacific Northwest Stream

Interactive effects of climate change and anthropogenic disturbances are warming streams. As temperature rises, resident species must adapt or migrate, resulting in altered life history strategies and novel species interactions. Exacerbating these changes are introduced warm-water predators, such as smallmouth bass (Micropterus dolomieu), that expand upstream and negatively impact native species. For instance, in the Columbia River Basin, smallmouth bass has appreciably expanded upstream and is now sympatric with subyearling Chinook salmon (Oncorhynchus tshawytscha). Integral to understanding upstream range expansion potential of bass is to examine its reproductive success and juvenile recruitment at range boundaries. We explore this in the John Day River where bass occupy the upstream limit of its thermal tolerances. Our objectives were to characterize the leading edge of distribution, determine life history attributes of reproductive adults and quantify spatiotemporal variability in nesting patterns and juvenile growth. Reporting on a spatially extensive (50+ km) longitudinal survey of reproductive behavior and recruitment success, our results suggest that juvenile growth drives colonization success, but adult overwinter location dictates the leading edge of invasion. This research highlights how understanding stage specific sensitivities to stream temperature is critical for predicting future distributional potential of invasive fishes and ultimately guiding management practices.