Retrospective Analysis of Smallmouth Buffalo (Ictiobus bubalus) Flow-Recruitment Relationships in Multiple Rivers Reveals Importance of High-Flow Pulses

Development of environmental flows standards to support biodiversity and ecosystem services is critical for effective water management yet remains daunting. Rate-based studies of flow-ecology relationships are expected to facilitate mechanistic understanding of system dynamics and support forecasting responses to environmental flow scenarios. Contemporary age-structure data and retrospective flow analyses were used to model effects of the flow regime on annual recruitment of Smallmouth Buffalo, a long-lived periodic life-history species, in three river basins. Model selection procedures used a two-tiered approach to identify attributes of the flow regime during the spawning season that were correlated with recruitment index values, as well as antecedent and post-spawn flow attributes that improved model fit. Smallmouth Buffalo lived more than 60 years in the study basins, and recruitment index values were highly variable among years. High pulse length during the spawning season was positively correlated with recruitment, was included in all competing models and was a critical contributor to significant models with high explanatory power. Conversely, recruitment was negatively correlated with high pulse number and the date of max flow during the spawning season. Our study demonstrates the utility of rate-based approaches for understanding flow-ecology relationships and our findings support the importance of high flow pulses of sufficient magnitude, duration, and timing for Smallmouth Buffalo spawning and successful recruitment. Models elucidating hydrological drivers of recruitment success in indicator taxa like Smallmouth Buffalo can be used to forecast population responses to alternative scenarios of flow management and environmental change.