Using coded-wire-tag recovery to investigate the early marine migration of juvenile salmon in the Strait of Georgia: implication for growth and survival

Pacific salmon have a complex life cycle that involves both freshwater and marine phases, though it is in the marine environment that they spend the greater part of their lives and gain the bulk of their mass and energy that will subsequently be used for reproduction. An assessment of when and where they migrate to in the ocean is critical first step to understand how the marine environment affects Pacific salmon. In the Strait of Georgia, juvenile salmon leave their natal river in the spring and summer, may reside inshore for some period of time before moving to the offshore waters of the Strait of Georgia and eventually onto the continental shelf and Gulf of Alaska before returning to their natal river to spawn. Although this general migration pattern has long been known, information on the migration behaviour of individual populations is generally lacking, due to the logistical difficulty of inferring the migration of from catch data alone. Here we synthesize 17 years of coded-wire-tag (CWT) recovery data from trawl surveys conducted in the Strait of Georgia to infer the early marine distribution and dispersal of juvenile Coho salmon and Chinook salmon. We also compared the change in the size of the dominant populations in relation to their ocean entry location and marine distribution, and examine the relationship between smolt survival and capture size of these populations