SPATIAL VARIATIONS IN FEEDING AND CONDITION OF JUVENILE PINK AND CHUMSALMON OFF VANCOUVER-ISLAND, BRITISH-COLUMBIA

Spatial variations in feeding and condition of juvenile pink (Oncorhyn chus gorbuscha) and chum (Oncorhynchus keta) salmon, and their implica tions for growth, were examined on the Vancouver Island continental sh elf in early summer 1992. Juvenile pink salmon off northern Vancouver Island had more material in their stomachs, were in better condition, and had higher potential growth rates (from a bioenergetics model) tha n pink salmon off southern Vancouver Island. These variations were con sistent with spatial differences in zooplankton biomass, there being m ore plankton in the northern region. There was a significant positive relationship between condition of pinks and the amount of material in their stomachs, suggesting a positive feedback on feeding success. Juv enile chum in the north also had more material in their stomachs than chum to the south. However, condition factor was not significantly dif ferent between southern and northern regions nor was there a significa nt relationship between condition factor and the weight of stomach con tents for chum on the southern shelf. A bioenergetics model suggests t hat chum in the south were food limited. Stable carbon isotope data al so indicated different feeding histories for some chum in the southern region, which may have been recent migrants onto the continental shel f from near-shore areas, or possibly a nearby hatchery. Estimation of the energy required by juvenile salmon to migrate north in a continent al shelf area with low zooplankton biomass and a weak northerly curren t (inner shelf), compared with an area with higher zooplankton biomass but a strong southerly current (outer shelf), indicated sufficient su rplus energy only in the inner shelf, consistent with observations of northward migrations predominantly through this area. Spatial variatio ns in current velocity and zooplankton biomass can affect feeding, con dition, and potential growth of juvenile pink and chum salmon off Vanc ouver Island.