![]() For Atlantic salmon, the use of archival tags has expanded our knowledge of where they feed in the ocean 12, 23, 24, 25, 26 and provided detailed data on individuals’ depth and temperature use 27, 28, 29. The development of electronic tracking technologies has opened new possibilities to collect detailed spatially unbiased information on fish migrations and individual behaviour over large ocean areas 21, 22. They have also provided little information on detailed migration routes and behaviour. These previous studies have been spatially limited by primarily sampling from fisheries and surveys at the Faroes, Greenland and in the Norwegian Sea 20 rather than over more widespread regions that Atlantic salmon are believed to use. More recently, genetic studies have disentangled novel aspects of the species’ ocean migration and distribution 17, 18, 19. Traditionally, information on the ocean migration originated from sampling and conventional tagging surveys based on mark and recapture methods 15, 16. The Atlantic salmon is one of the world’s most studied fish, but detailed knowledge of its ocean distribution and behaviour is limited. With knowledge of the oceanic distribution of salmon from different regions, the causative mechanisms underlying the variation in growth and productivity can be better understood. A key element in identifying and evaluating factors that contribute to reduced survival is knowledge of migration routes, migration timing and feeding areas. However, the causal links between ocean processes and survival remain elusive. This has increased interest in the spatio-temporal ocean distribution of Atlantic salmon 11, 12 and the impacts of the ocean environment on individual growth and survival 13, 14. One of the major hypotheses for the decline is reduced marine survival 9, 10. In Europe and North America, the abundance of Atlantic salmon has generally declined since the 1970s 9, 10. It has been suggested that many of these species have expanded their marine feeding areas northwards 7, 8, resulting in longer migration distances to foraging areas. Diadromous Atlantic salmon ( Salmo salar) and Pacific salmon ( Oncorhynchus spp.) spawn and spend the juvenile phase in rivers and perform long-distance ocean feeding migrations 5, 6. Temperatures have increased in the north Atlantic and Pacific oceans over the last few decades, causing large-scale oceanographic changes 1, 2 and northward distributional shifts of many species 3, 4. Climate-induced changes in oceanographic conditions will alter the location of frontal areas and may have stock-specific effects on Atlantic salmon population dynamics, likely having the largest impacts on southern populations. Dissimilarities in distribution likely contribute to variation in growth and survival within and among populations due to spatio-temporal differences in environmental conditions. The oceanic distribution differed among individuals and populations, but overlapped more between geographically proximate than distant populations. Individuals migrated further north and east than previously reported and displayed increased diving activity near oceanographic fronts, emphasizing the importance of these regions as feeding areas. We attached 204 pop-up satellite archival tags to post-spawned salmon when they migrated to the ocean from seven European areas and maiden North American salmon captured at sea at West Greenland. Determining the mechanisms driving range-wide reductions in Atlantic salmon marine survival is hindered by an insufficient understanding of their oceanic ecology and distribution.
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