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Objective: Coho Salmon Oncorhynchus kisutch provide an important resource for recreational, commercial, and Indigenous fisheries in the Pacific Northwest. The goal of this study was to improve our understanding of how marine mammal predation may be impacting the survival and productivity of Coho Salmon in the Strait of Georgia, British Columbia. Specifically, we quantified the impact of harbor seal Phoca vitulina predation on juvenile Coho Salmon during their first several months at sea. Early marine survival is believed to be the limiting factor for the recovery of Coho Salmon populations in this region. Methods: To estimate the number of juvenile Coho Salmon consumed by harbor seals, we developed a mathematical model that integrates predator diet data and salmon population and mortality dynamics. Result: Our analysis estimated that harbor seals consumed an annual average of 46−59% of juvenile Coho Salmon between 2004–2016, providing the first quantitative estimate of seal predation in the Strait of Georgia. Conclusion: Marine mammal predation on juvenile Coho Salmon is potentially a very important factor limiting survival and recovery of Coho Salmon in the Strait of Georgia. Impact statementCoho Salmon populations in the Strait of Georgia have experienced precipitous declines in marine survival over the last four decades. In this study, we used predator diet data to quantify the potential impact of harbor seals on juvenile Coho Salmon. Our results suggest seal predation may strongly influence survival of young salmon during their first several months at sea, and should be considered in future recovery efforts. [ABSTRACT FROM AUTHOR]