Effective number of breeders provides a link between interannual variation in stream flow and individual reproductive contribution in a stream salmonid

The effective number of breeders that give rise to a cohort (Nb) is a promising metric for genetic monitoring of species with overlapping generations; however, more work is needed to understand factors that contribute to variation in this measure in natural populations. We tested hypotheses related to interannual variation in Nb in two long-term studies of brook trout populations. We found no supporting evidence for our initial hypothesis that inline image reflects inline image (defined as the number of adults in a population at the time of reproduction). inline image was stable relative to inline image and did not follow trends in abundance (one stream negative, the other positive). We used stream flow estimates to test the alternative hypothesis that environmental factors constrain Nb. We observed an intermediate optimum autumn stream flow for both inline image (R2 = 0.73, P = 0.02) and full-sibling family evenness (R2 = 0.77, P = 0.01) in one population and a negative correlation bet...