Life History Patterns of Juvenile Coastal Coho Salmon in Southern Oregon

Early coho salmon life history has been described as consisting of a single strategy: freshwater residence for the first year of life followed by yearling smolt migration to sea. However, there is evidence suggesting the existence of alternative life histories, particularly on coastal populations. We monitored the movement of PIT tagged juvenile coho salmon and used otolith micro-chemistry to identify the prevalent resident and nomadic strategies and examine possible relationships between those strategies and fish body mass, growth and apparent survival in a southern Oregon coastal watershed. Our results show that mobile juvenile coho salmon were larger and grew faster than sedentary individuals. Apparent survival to smolting was greater in summer among sedentary than mobile fish, but did not differ in winter. Some years, the proportion of spawners that had migrated to the estuary as subyearlings was higher than that of fish that smolted as yearlings. Four main life histories were identified: migrating fry, migrating parr, migrating parr re-entering freshwater and leaving as yearlings (“nomads”), and yearling smolts. This diversity of life histories reflect the capacity for plastic behavior in coho salmon and the importance of managing both freshwater and estuarine nursery habitats to sustain this species.