Three Decades of Farmed Escapees in the Wild: A Spatio- Temporal Analysis of Atlantic Salmon Population Genetic Structure throughout Norway

摘要

Each year, hundreds of thousands of domesticated farmed Atlantic salmon escape into the wild. In Norway, which is theworld’s largest commercial producer, many native Atlantic salmon populations have experienced large numbers of escapeeson the spawning grounds for the past 15–30 years. In order to study the potential genetic impact, we conducted a spatiotemporalanalysis of 3049 fish from 21 populations throughout Norway, sampled in the period 1970–2010. Based upon theanalysis of 22 microsatellites, individual admixture, FST and increased allelic richness revealed temporal genetic changes insix of the populations. These changes were highly significant in four of them. For example, 76% and 100% of the fishcomprising the contemporary samples for the rivers Vosso and Opo were excluded from their respective historical samplesat P = 0.001. Based upon several genetic parameters, including simulations, genetic drift was excluded as the primary causeof the observed genetic changes. In the remaining 15 populations, some of which had also been exposed to high numbersof escapees, clear genetic changes were not detected. Significant population genetic structuring was observed among the21 populations in the historical (global FST = 0.038) and contemporary data sets (global FST = 0.030), although significantlyreduced with time (P = 0.008). This reduction was especially distinct when looking at the six populations displaying temporalchanges (global FST dropped from 0.058 to 0.039, P = 0.006). We draw two main conclusions: 1. The majority of the historicalpopulation genetic structure throughout Norway still appears to be retained, suggesting a low to modest overall success offarmed escapees in the wild; 2. Genetic introgression of farmed escapees in native salmon populations has been stronglypopulation-dependent, and it appears to be linked with the density of the native population.