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Baltic salmon

Salmo salar

Photo: Ingemar Pettersson/AzotePhoto: Ingemar Pettersson/Azote

The salmon reproduces in rivers across the whole Baltic Sea. Juveniles stay in freshwater streams for one to four years and then spend one to several years at sea on a feeding migration before they return to spawn in their natal river.

Conservation genetic management advice

  • Manage each population separately. Protect populations within each river.
  • Restore spawning habitats.
  • Avoid mixed fisheries and large scale stocking.
  • Phase out large scale releases. For conservation releases to support or reestablish weak or extinct populations, use genetically close populations.
  • The occurrence of two major lineages within the Baltic Sea should be taken into account. Transplantations between these phylogeographic lineages should be strictly avoided.

Threats to genetic biodiversity

The Baltic salmon is subjected to large scale fishing which is expected to affect both fish abundance and genetic diversity. Mixed fisheries and large scale releases threaten remaining gene pools and naturally spawning stocks.

Hatchery breeding often uses too small populations which risks depletion of genetic diversity over time. Genetic homogenization in wild populations from releases is documented and could result in, for example, loss of genetic adaptations.

Power plant constructions have blocked migratory routes between spawning and feeding grounds in many rivers around the Baltic Sea. Only around 30 percent of previous salmon rivers harbour wild populations today.

Knowledge on genetics in the Baltic (2017)

Salmon is without comparison the genetically most well studied species in the Baltic Sea. The Baltic salmon is genetically differentiated from other salmon populations in Europe and in the Atlantic Ocean. Strong homing to natal spawning grounds results in a pronounced genetic substructure, where each river harbours at least one genetically unique population. A relatively large proportion of the species genetic variation is due to differences between populations inhabiting different rivers.

The majority of the natural populations are lost, and not all of those remaining are sustainable. Effective size of local populations and for the Baltic populations as a whole is depleted.

Baltic salmon exhibit lower genetic variation than Atlantic populations, probably due to bottleneck events during the colonization of the Baltic Sea after the last ice age. The genetic dichotomy in Baltic salmon, where northern and eastern populations form two different genetic groups, is most likely an effect of two colonizing lineages.

References


CONTRIBUTORS 

Linda Laikre
linda.laikre@popgen.su.se

Sara Kurland
sara.kurland@zoologi.su.se

Additional information

The population structure of Baltic salmon has been known since the mid 1980s. Already then it was clear that the species should be managed on a population by population basis, and that releases were potentially harmful to native gene pools.

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