Genetic Assessment of Salmon and Sea Trout Stocking in a Baltic Sea River

Microsatellite DNA variation were used to assess the outcome of stocking salmon and trout in River Saevara, N Sweden. No information on pre-stocking genetic composition of salmon and trout in R Saevara was available. In two year classes of salmon smolt microsatellite data indicated that post-stocking genetic composition differed markedly (Fst = 0.048) from the main donor strain, Byskeaelven salmon, and from other Gulf of Bothnia salmon stocks (Fst 0.047- 0.132). The STRUCTURE program failed to detect any sub structuring within Saevara salmon. It was concluded that only minor introgression estimated to a proportion of 0.11 (95% CI 0.07 - 0.16) has occurred in salmon. Sea migrating trout showed overall low differentiation among populations with maximum Fst of 0.03 making analysis more cumbersome than in salmon. Still, the Saevara trout deviated significantly from potential donor populations and structure software supported that majority of trout in Saevara formed a distinct genetic population. Admixture was more extensive in trout and estimated to 0.17 (95% CI 0.10 - 0.25)

Overwintering and downstream migration of sea trout (Salmo trutta L.) kelts under regulated flows - northern Sweden

Post-spawning migrations of sea trout (Salmo trutta L.) in two northern Swedish river systems, Vindelalven and Pitealven, were studied. Telemetry was used to evaluate spawning locations, post-spawning mortality, overwintering survival/habitat selection/location, partitioned natural mortality from dam passage mortality and overall survival from post-spawning to the sea entry. Fifty-eight sea trout (L_T = 50-86 cm) were radio-tagged at the beginning of their spawning migration from June to September in 2003 and 2004, and their spawning in September and October each year was monitored. In total, 91% (n=53) survived spawning and were thus defined as kelts. Of these, 92% (n=49) overwintered under ice-cover in deep, slow flowing sections of the rivers. Overwintering mortality was low, on average 8%. The main seaward migration occurred during May and June and was initiated when ambient water temperatures exceeded 4-6 degrees Celsius, independent of the start of the spring flood when flows rose to 1000 m^3/s. The highest downstream migration speed was approximately 25km/24h and migrations mainly took place at daytime. During seaward migration, the kelts encountered hydropower stations that lacked bypass systems for fish passage, which delayed their downstream migrations. Passage mortality at the power stations was 69 and 25% in the Vindelalven and Pitealven, respectively. These losses, combined with the naturally high winter survivals of kelts at the unregulated river parts, underline the importance of developing safe passage routes for kelts at hydropower facilities for conserving sea trout populations in regulated rivers

High variability in spawning migration of sea trout, Salmo trutta, in two northern Swedish rivers

Telemetry was used to examine spawning migration of sea trout, Salmo trutta L. (n = 126), in two rivers in northern Sweden. The spawning areas defined by radio-tagged fish differed between the river systems. In the River Vindelaelven, sea trout spawned in the main stem and 80% of tagged individuals returned to areas where hatchery-reared juveniles had been previously stocked. In the River Piteaelven, 74% of tagged sea trout ascended tributaries for spawning. Tagged fish were categorised into three groups of migratory pattern. CART (classification and regression tree) analysis indicated that distance from tagging location to spawning site (Sdist) explained the migratory patterns. Large Sdist separated fish with stepwise upstream migration from those with up- and downstream migrations and one-directional direct migration. Fish tagged early in the season migrated the longest distance to spawning areas. Stocking locations and sex explained the large search behaviour up- and downstream in the rivers. The findings are important for the sustainable management of sea trout in the Gulf of Bothnia

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)