Gene flow and conservation of genetic variation in anadromous Atlantic salmon (Salmo salar)

An estimate for effective migration among populations of anadromous Atlantic salmon is Nm < 1 under the assumptions of the n‐island model, where N is the effective population size, and m is the migration rate. For populations less than 1000‐2000 kilometers apart the estimate is Nm > 1. The gene flow estimation is based on (i) the use of the coefficient FST and (ii) Slatkin's method of conditional average frequencies of alleles and (iii) his method of rare alleles as indicators. Two data sets were constructed from protein polymorphism studies. The first involved allele frequences of the 4 most variable loci at 89 sampling locations, and the second included 38 loci at 57 locations. Locations cover the whole distribution of the Atlantic salmon, including the Baltic Sea, and Eastern and Western Atlantic Ocean. Only anadromous and natural populations with a minimum sample size of 10 individuals were included. Mean sample sizes were 66 and 56 individuals per location in the data sets one and two, respectively. Three approximate limits are suggested to define the units for conservation of genetic variation, Nm = 1, 4Ns = 1, and m/s = 1, where s is the selection coefficient. Based on these limits, six propositions are derived. The propositions are used to evaluate situations where selection overcomes the effects of random drift and gene flow. Response of population to local selection is proposed as a criterion in preservation of genetic variation for breeding and ranching purposes.