Anadromous salmonid fishes frequently exhibit strong geographic population structuring. However, population genetic differentiation of Atlantic salmon (Salmo salar) at fine geographic scales differs across equivalent spatial extents in different regions. So far, fine-scale genetic differentiation has not been assessed in rivers of the Baltic Sea, a region that contains an evolutionarily distinct Atlantic salmon lineage. Thus, Baltic salmon are currently managed on the river level, without focus on potential genetic structure and diversity within rivers. Here, we used microsatellites to characterize the genetic structure of wild juvenile salmon sampled throughout the interconnected, northern Baltic Tornio and Kalix Rivers. We found genetic differentiation within the two rivers, but not between them: salmon in the upper reaches differed from individuals in the lower reaches, regardless of river system. Further, examining smolts migrating from the river to the sea and adults returning from the sea to spawn, we found an association between the genetic structure and seasonal migration timing. Out-migrating smolts genetically assigned to upper river reaches were older and tended to reach the sea later in the season than smolts from the lower reaches. In contrast, mature adults originating from the upper reaches returned to the river early in the season. Our observation of genetic population structuring between downstream and upstream reaches of the large Tornio and Kalix rivers, and its association with migration timing, implies that careful temporal management of the northern Baltic fisheries would help to preserve the diversity and sustainability of the wild salmon stocks of these rivers.

淡水鲑科鱼类经常表现出强大的地理种群结构。然而，大西洋鲑（Salmo salar）的种群遗传分化）在精细的地理尺度上在不同区域的等效空间范围内有所不同。到目前为止，尚未在波罗的海的河流中评估精细的遗传分化，该地区包含进化上截然不同的大西洋鲑鱼谱系。因此，波罗的海鲑鱼目前在河流一级进行管理，而没有关注河流内潜在的遗传结构和多样性。在这里，我们使用微卫星来表征整个北波罗的海托尔尼奥河和加利克斯河相互连接的野生鲑鱼的遗传结构。我们发现了两条河流之间的遗传分化，但没有发现它们之间的差异：上游的鲑鱼与下游的个体有所不同，而与河流系统无关。此外，研究从河中迁徙到海中的软体动物和从海中返回并产卵的成年鸟类，我们发现遗传结构和季节性迁徙时机之间存在关联。从基因上分配给上游河段的迁出的mol鱼比来自下游河段的鱼更老，并且往往在本季节晚些时候到达海洋。相反，来自上游的成年成年人则在本季节初返回河中。我们观察到Tornio和Kalix大河下游和上游河段之间的遗传种群结构及其与迁徙时机的关系，这意味着对波罗的海北部渔业进行认真的时间管理将有助于保持野生鲑鱼种群的多样性和可持续性。这些河流。从基因上分配给上游河段的迁出的mol鱼比来自下游河段的鱼更老，并且往往在本季节晚些时候到达海洋。相反，来自上游的成年成年人则在本季节初返回河中。我们观察到Tornio和Kalix大河下游和上游河段之间的遗传种群结构及其与迁徙时机的关系，这意味着对波罗的海北部渔业的谨慎时间管理将有助于保持野生鲑鱼种群的多样性和可持续性。这些河流。从基因上分配给上游河段的迁出的mol鱼比来自下游河段的鱼更老，并且往往在本季节晚些时候到达海洋。相反，来自上游的成年成年人则在本季节初返回河中。我们观察到Tornio和Kalix大河下游和上游河段之间的遗传种群结构及其与迁徙时机的关系，这意味着对波罗的海北部渔业进行认真的时间管理将有助于保持野生鲑鱼种群的多样性和可持续性。这些河流。