Effects of poor recruitment on riverine Smallmouth Bass population dynamics.

Objective: Altered flow regimes pose significant risks to the stability of populations of riverine Smallmouth Bass Micropterus dolomieu. Periods of poor recruitment, due to early life stage mortality resulting from high-flow events, can cause size-structure and density alterations of populations. The aim of this study was to opportunistically test for changes in dynamic rates of a riverine Smallmouth Bass population using a long-term data set that spanned a period of poor recruitment. Methods: Our study evaluated size-specific CPUE (fish/h), mortality, growth, and condition and tested for recruitment determinants of Smallmouth Bass through three consecutive years of poor age-0 recruitment in the South Branch Potomac River, West Virginia. We used fall nighttime boat electrofishing surveys during 2009-2022 to monitor this population before and after the poor-recruitment time frame (2016-2018). Result: Age-0 CPUE was greater during the time frame prior to the poor-recruitment time frame. However, there was no difference in the CPUE of quality-length Smallmouth Bass between the two time frames and CPUE of preferred-length fish was greater during the poor-recruitment time frame. Growth and relative weight increased during the poor-recruitment time frame. There was no significant difference detected in mortality between the recruitment time frames. Streamflow during the spawning period was a significant factor influencing fall recruitment of age-0 Smallmouth Bass. A Ricker density-dependent model with an added streamflow term performed as well as a basic, log-linear streamflow model and a density-independent model that also incorporated a streamflow term. Conclusion: Our results provide evidence of density-dependent structuring in this population. Decreases in population density increased population dynamic rates that maintained or improved size structure. High adult biomasses did not increase age-0 recruitment. Many riverine Smallmouth Bass populations may display favorable density-dependent responses to declines in juvenile recruitment. Thus, management agencies should better understand the resiliency of these populations prior to establishing expensive programs or regulations, which may be ineffective, to combat alterations in juvenile recruitment. [ABSTRACT FROM AUTHOR]