Genetic changes in Atlantic salmon stocks since historical times and the effective population size of a long-term captive breeding programme

Human-caused genetic changes in two Atlanticsalmon (Salmo salar L.) stocks, from therivers Iijoki and Oulujoki in Finland, wereassessed by comparing the genetic parameters ofthese stocks before and after the hatcherybreeding of several successive generations,corresponding to 40 and 33 years since the wildstate. The changes were also compared withthose observed in a large wild salmon stock inthe River Teno during 56 years. In all, thevariation at seven microsatellite DNA loci wasexamined in 11 Atlantic salmon samplesoriginating from these three rivers. Theeffective population size, N_e, duringbreeding of the Iijoki broodstock and for theTeno salmon was also estimated by the temporalmethod based on allele frequency changes. Forthe Iijoki broodstock, the changes could betracked generation by generation from thefounding of the stock. Statisticallysignificant changes in allele frequencies werecommon in the hatchery stocks (F = 0.029, forIijoki), but not in the wild Teno stock, whichwas temporally very stable (F = 0.007). Allelicrichness decreased statistically significantly(24.8%) in the Oulujoki broodstock, from 62.1to 46.7 alleles at nine loci. On average, therewere 9.7 fewer alleles (15.7%) in thecontemporary broodstocks than in thecorresponding historical stocks. The meanheterozygosity was 6.6% lower in thecontemporary Oulujoki broodstock, but remainedunchanged in the Iijoki broodstock. Theestimated N_e for the Iijoki broodstock wasunder 80 for 4.5 generations from 1962 to 1995and for the wild Teno salmon over 900 for 56years from 1939 to 1995.