Impact of human‐induced environmental changes on genetic structure and variability in Atlantic salmon, Salmo salar

The genetic effects on Atlantic salmon, Salmo salar L., populations from potential bottleneck situations caused by human activities in two Norwegian rivers, Laerdalselva and Batnfjordelva, were studied by analysing DNA from fish scales collected before and after the populations had been exposed to human-induced changes: river regulation, Gyrodactylus salaris infection and rotenone treatment. Using 15 microsatellites, no significant changes were found in the genetic structure and diversity of four population samples from Laerdalselva collected over 34years. However, salmon from Laerdalselva were significantly differentiated from nearby (angstrom rOyelva) and more distant (Batnfjordelva and Suldalslagen) populations, testifying to the power of the marker system to detect small genetic differences. Furthermore, two population samples from Batnfjordelva, collected 20years apart, showed low but significant differentiation. The lack of effects on neutral genetic composition in Laerdalselva, despite several potentially severe bottleneck events, indicates that stocking and sea cohorts maintain the status quo of this population.