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).
KEYWORDS: Genetic assignment; Genetic introgression; Salmo salar; Salmo trutta; Stocking

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