Quantifying impacts of harbor seal Phoca vitulina predation on juvenile Coho Salmon in the Strait of Georgia, British Columbia

Abstract

AbstractObjectiveCoho 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.MethodsTo 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.ResultOur 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.ConclusionMarine mammal predation on juvenile Coho Salmon is potentially a very important factor limiting survival and recovery of Coho Salmon in the Strait of Georgia.