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salmonnb: a program for computing cohort-specific effective population sizes (Nb) in Pacific salmon and other semelparous species using the temporal method


Robin Waples, Fax: (206) 860–3335; E-mail:


We describe a new method and a computer program salmonnb to calculate the effective number of breeders (Nb) per year in semelparous species with variable age at maturity. The existing temporal method for the ‘salmon’ life history produces an estimate of the harmonic mean Nb in the two sampled years. salmonnb reads genotypic data in standard formats and computes yearly Nb values by combining information from pairwise comparisons of samples taken in 3 or more years. Simulations show that the new method produces unbiased estimates of yearly Nb, and precision is inversely proportional to true effective size.