ROLE OF A RIVERINE PLUME AS A NURSERY AREA FOR CHUM SALMON ONCORHYNCHUS-KETA

We examined the spatial distribution of juveniles in coastal water to assess how riverine plumes serve as nursery areas for chum salmon in e arly ocean life. The distribution of juveniles was restricted within a low-salinity water mass that was formed by riverine discharges. We de tected 2 juvenile sizes at which distributions changed. Distributions of small juveniles (less than or equal to 50 mm in fork length) and me dium-size juveniles (50 to 75 mm) were found in nearshore regions and were less affected by water temperature and salinity. Distributions of large juveniles (>75 mm) were located in waters whose salinity was 25 to 30 psu, and were less-affected by the distance from the shoreline. Results suggested that the juvenile distribution was affected by tole rance to environmental stress (high temperature or high salinity) and by refuge from fish predators. Juvenile chum salmon can use riverine p lume habitats to avoid environmental stress, to search for prey patche s, and to expend less energy for migration.