Genetic assessment of Atlantic salmon Salmo salar and sea trout Salmo trutta stocking in a Baltic Sea river

Microsatellite DNA variation was used to assess the outcome of stocking Atlantic salmon Salmo salar and migratory trout Salmo trutta in River Savara, N Sweden. No information on pre-stocking genetic composition of S. salar and S. trutta in River Savara was available. In 2 year-classes of S. salar smolt, microsatellite data indicated that post-stocking genetic composition differed markedly (F-ST = 0.048) from the main donor strain, Byskealven S. salar, and from other Gulf of Bothnia S. salar stocks (F-ST 0.047 and 0.132). The STRUCTURE programme failed to detect any substructuring within Savara salmon. It was concluded that only minor introgression estimated to a proportion of 0.11 (95% CI 0.07-0.16) has occurred in S. salar. Salmo trutta showed overall low differentiation among populations with maximum F-ST of 0.03 making analysis more cumbersome than in S. salar. Still, the Savara S. trutta deviated significantly from potential donor populations, and STRUCTURE software supported that majority of trout in Savara formed a distinct genetic population. Admixture was more extensive in S. trutta and estimated to 0.17 (95% CI 0.10-0.25). (C) 2008 The Authors.