Ocean predation and mortality of adult Atlantic salmon

• Published in: Scientific Reports
• Main Authors: Strøm, John Fredrik, Rikardsen, Audun Håvard, Campana, Steven, Righton, David, Carr, Jonathan, Aarestrup, Kim, Stokesbury, Michael J. W., Gargan, Patrick, Javierre, Pablo Caballero, Thorstad, Eva Bonsak
• Other Authors: Líf- og umhverfisvísindadeild (HÍ), Faculty of Life and Environmental Sciences (UI), School of Engineering and Natural Sciences (UI), Verkfræði- og náttúruvísindasvið (HÍ), Háskóli Íslands, University of Iceland
• Format: Article in Journal/Newspaper
• Language: English
• Published: Springer Science and Business Media LLC 2019
• Subjects: Ecology; Ichthyology; Vistfræði; Fiskifræði; Atlantshafslax; Alta; Canada; Jaakko; Norway; Tromsø; Atlantic salmon; North Atlantic; Salmo salar; toothed whales
• Online Access: https://hdl.handle.net/20.500.11815/1570; https://doi.org/10.1038/s41598-019-44041-5

Publisher's version (útgefin grein). Predation and mortality are often difcult to estimate in the ocean, which hampers the management and conservation of marine fshes. We used data from pop-up satellite archival tags to investigate the ocean predation and mortality of adult Atlantic salmon (Salmo salar) released from 12 rivers fowing into the North Atlantic Ocean. Data from 156 tagged fsh revealed 22 defnite predation events (14%) and 38 undetermined mortalities (24%). Endothermic fsh were the most common predators (n=13), with most of these predation events occurring in the Gulf of St. Lawrence and from the Bay of Biscay to the Irish Shelf. Predation by marine mammals, most likely large deep-diving toothed whales (n=5), and large ectothermic fsh (n=4) were less frequent. Both the estimated predation rates (ZP) and total mortality rates (ZM) where higher for Atlantic salmon from Canada, Ireland, and Spain (ZP=0.60– 1.32y−1, ZM =1.73–3.08y−1) than from Denmark and Norway (ZP=0–0.13y−1, ZM =0.19–1.03y−1). This geographical variation in ocean mortality correlates with ongoing population declines, which are more profound for southern populations, indicating that low ocean survival of adults may act as an additional stressor to already vulnerable populations. We thank Alta Laksefskeri Interessentskap, Atlantic Salmon Conservation Foundation, Danish Rod and Net License Fund, Inland Fisheries Ireland, Miramichi Salmon Association, Research Council of Norway project 280308 SeaSalar, Tromsø Research Foundation, and Xunta de Galicia for supporting and funding this project. We also thank all staf, students, and volunteers who have contributed to the feldwork, and Timothy F. Sheehan and Jaakko Erkinaro for insightful discussion on an earlier version of the manuscript. Peer Reviewed