Climate Impacts on the Marine Survival of Atlantic Salmon

Survival during the first year at sea is the main determinant of Atlantic salmon recruitment. Recruitment appears to be related to basin scale climate variation in the form of the Atlantic Multi-decadal Oscillation. Sea surface temperature variation during the spring period when smolts enter the marine environment correlates with North America survival rate whereas Europe survival is correlated with late summer sea surface temperatures. This differential response to climate is reflected in a differing role of post-smolt growth and predation pressure on smolts. European post-smolt growth has varied in correlation to the recruitment patterns for southern European stocks, consistent with the hypothesis that growth governs the accumulated mortality during the post-smolt year in these stocks. Post-smolt growth does not appear to have the same effect on North American stocks where post-smolt growth has increased in recent years while survival has declined. North American Atlantic salmon recruitment appears to be governed by variation in predation pressure during the first months at sea. The persistent range of Atlantic salmon in North America and Europe may be redefined by the dynamics of ocean thermal conditions in combination with stressors associated with other segments of its life history.