Smallmouth bass recruitment variability and its relation to stream discharge in three Virginia rivers

The recruitment of smallmouth bass Micropterus dolomieu in rivers commonly exhibits a high degree of annual variation. We examined three rivers in Virginia with the objectives of determining the magnitude of recruitment variability, identifying a functional index for measuring year-class strength, and examining the relationship between stream discharge and recruitment success. Recruitment in the three study rivers varied by as much as an order of magnitude among years. The electrofishing catch per unit effort of age-0 smallmouth bass in September-November was a reliable measure of year-class strength. The recruitment success of smallmouth bass was significantly related to mean June streamflow using a nonlinear model, with the strongest year-classes produced in years with moderate flows. Mean June streamflow reasonably predicted the abundance of age-0 smallmouth bass in the fall. Our data suggest that stream discharge during and immediately after spawning could be critical to smallmouth bass recruitment success.