Adult Atlantic salmon (Salmo salar) return from the ocean to spawn in single stream reaches, but the life history of juveniles during their freshwater phase is less certain, due largely to the difficulty of tracking individuals. A better understanding of this life stage would be helpful for improving conservation and management strategies. Kennedy et al. have measured strontium isotope ratios in salmon otoliths--ear stones formed from concentrically deposited layers of calcium carbonate--and used these to reconstruct their habitats; different streams have distinct isotopic signatures that are determined by the underlying bedrock of the watersheds. The Sr ratios reveal that some juvenile Atlantic salmon, which have been assumed to move no more than 50 m during their 2-year freshwater residence, can move back and forth between habitats or even steadily downstream in the course of becoming smolts. -- HJS
Can. J. Fish. Aquat. Sci. 59, 925 (2002).
