Genetic differentiation and gene flow in Atlantic salmon,Salmo salar L.: a case study of the River Shannon system in Ireland

An analysis of the effect of an extensive restocking programme on genetic differentiation and gene flow of the Atlantic salmon, Salmo solar L., in the River Shannon system in Ireland is presented, using allozyme electrophoresis to estimate population differentiation. The observed differentiation in the River Shannon is attributed to random genetic drift, caused by small effective population sizes in some of the tributaries, coupled with the confounding effect of extensive stocking of indigenous fish which were largely derived from a single tributary. The methods of analysis are assessed by applying numerical resampling techniques to determine confidence levels for each of the estimates.