Spatiotemporal Spawning Patterns of Smallmouth Bass at Its Upstream Invasion Edge

Abstract

Climate 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

Acknowledgments

We thank Lucinda Morrow from Washington Department of Fish and Wildlife for conducting age analysis on our Smallmouth Bass scales; David Lawrence for providing temperature and habitat data; two anonymous reviewers for their constructive comments, and Chris Repar, Travis Hedrick, and Michelle Louie for field assistance. Particular appreciation goes to all the landowners of the North Fork John Day River for access to their land and endless support throughout the years. Funding support was provided by the Northwest Climate Science Center graduate fellowship, grants from Anchor QEA and Northwest Scientific Association and the University of Washington H. Mason Keeler Endowed Professorship awarded to Julian Olden. Handling and care of vertebrates during this investigation were covered under the auspices of the University of Washington Office of Animal Welfare IACUC protocol 4172-07.