Partitioning the Sea: Advances in Understanding the Ocean Ecology of Gulf of Maine Atlantic Salmon

Gulf of Maine Atlantic Salmon, at the species southern North American range, undertake extensive ocean migrations into the North Atlantic. Increased natural mortality at sea is considered a primary threat that constrains recovery of this endangered species. Our goal was to partition ocean use in time and space to better investigate and understand limiting factors.  We used multiple methods: smolt trapping, marking, acoustic and satellite telemetry, pelagic trawls, fishery sampling, and modeling. For smolts, estuaries act primarily as corridors (not nurseries) and migration is shifting earlier in response/adaptation to changing climate. Hatchery smolts differ in their early marine diets and despite similar epipelagic migratory patterns have lower ocean survival than naturally-produced fish.  Migration continues at a rapid pace with postsmolts exiting US waters in 3 weeks. While at sea US Atlantic Salmon were exploited in numerous foreign mixed-stock fisheries.  Primary marine feeding areas are the Labrador Sea and the coast of West Greenland and although marine diets have remained relatively stable, total energy consumed has decreased.  Modelling has identified that climate and ecosystem drivers of Northwest Atlantic conditions directly and indirectly influenced salmon abundance and productivity. Collectively, these studies have increased our understanding of ocean ecology.