Tuesday March 31, 2026
California WaterBlog —
Wild Pacific salmon and trout exhibit complex variation in completing their life cycle. Within a single population, some individuals leave their natal (birth) streams soon after they emerge from the nest to begin their seaward migrations, while others remain for several months or years before migrating downstream. During their downstream migration, areas throughout a watershed, such as tributaries, floodplains, and estuaries, can serve as habitat for juvenile salmon to rear and grow. Chinook salmon, in particular, have adaptable and variable life histories that allow them to spread out across the landscape and rear in diverse environments and at different times. This spreading of the population reduces competition in any one environment and increases population productivity and resilience to disturbance.
Salmon raised in hatcheries, on the other hand, are confined to the hatchery until their release. In our recent study1 in the Sacramento River Basin, we evaluated the migratory patterns of hatchery Chinook salmon after their release and compared these patterns to those of Chinook salmon born in the river (i.e., “natural-origin”). We reconstructed their movement paths using otoliths, ear bones of fish that record, much like rings on a tree, the growth history of individual fish. The otolith chemical composition reflects the chemistry of the waters in which the fish was growing during that period of its life and thus provides a record of the different habitats the fish used during rearing and outmigration. Otoliths were collected from adult carcasses encountered by US Fish and Wildlife Service, California Department of Fish and Wildlife, and Pacific States Marine Fisheries Commission surveyors during spawning surveys and at Livingston Stone National Fish Hatchery by USFWS. Annual estimates of adult abundance and the biological samples collected from these programs are vital to understanding the status of salmon populations and reveals insights into their early lives, and which habitats they relied on as juveniles.