Spatiotemporal Spawning Patterns of Smallmouth Bass at Its Upstream Invasion Edge

Abstract

AbstractClimate change and land‐use practices are causing widespread warming of streams, forcing resident species to adapt or migrate. For instance, in the John Day River, Oregon (Columbia River basin), rising temperatures are facilitating the range expansion of Smallmouth Bass Micropterus dolomieu into critical salmon rearing habitat. Understanding Smallmouth Bass reproductive ecology at its range boundaries is integral to understanding and ultimately predicting its upstream range expansion. We addressed this knowledge gap by exploring potential temperature‐mediated effects on Smallmouth Bass reproduction at the leading edge of its nonnative riverine distribution in the Pacific Northwest. We used continuous snorkel surveys to characterize its upstream extent in the North Fork John Day River, where we observed spawning patterns and measured adult nest‐guarding male size, fecundity, brood development, habitat attributes, and nest success over 2 years (2014, 2015). We found a pattern of asynchronous and protracted spawn timing across the leading invasion edge, >90% nest success, and few changes in reproductive attributes (e.g., fecundity, brood development) as the thermal regime became increasingly colder. We also found increased selectivity of nest substrata and decreased guarding requirements in upstream habitats. These results suggest that reproductive success does not limit the upstream range expansion of Smallmouth Bass and highlight potential ecological benefits that may offset the energetic demands associated with dispersing upstream. Overall, our findings enhance the current understanding of how reproduction influences range expansion of nonnative Smallmouth Bass populations in streams, enabling us to better guide managers tasked with minimizing the spread of this nonnative species in the future.Received November 2, 2015; accepted February 1, 2016 Published online June 15, 2016