The genetic structure of sea trout (Salmo trutta L.) in Norway

Sea trout is the anadromous form of brown trout (Salmo trutta) and is culturally, economically, and ecologically important across its native distribution. Here, we describe the genetic structure of sea trout caught in 105 rivers from the 2600 km long Norwegian coast using >3000 individuals genotyped for 93 SNPs. Our results indicated that most of the study populations are genetically different from each other with a mean pairwise FST of 0.067. While most genetic variation was found within the different populations (93.2%), around 4.5% variation was found between rivers within the different fjord systems and neighbor joining analysis generally grouped together populations from the same fjord or geographic region. Isolation by distance (IBD) for the 105 populations was significant (r2 = 0.21), but the same analysis on three smaller spatial scales revealed different patterns: significant IBD in the Hardangerfjord, moderate IBD in the Sognefjord, and no IBD for the 28 most northern populations, altogether suggesting that there is not a simple relationship between geographic distance and genetic isolation. This documentation of sea trout intra-specific biodiversity must be considered in conservation of the intra-specific diversity of sea trout, including prioritizing habitat restoration, stocks included in genebank, and protection from negative impacts from aquaculture.