Prey relationships between juvenile pink (Oncorhynchus gorbuscha) and chum (O. keta) salmon in Prince William Sound, Alaska

Abstract

The food relationships between juvenile pink salmon (Oncorhynchus gorbusaha) and chum salmon (O. keta) released from a hatchery Prince William Sound are examined. Samples of zooplankton and salmon fry were collected from nearshore waters adjacent to the hatchery. Salmon fry in this area have little opportunity for spatial segregation by habitat and are obliged to use common food resources. An electivity index shows that both salmon fry species selectively prey upon available zooplankton. The diets of the two salmon species are compared using a measure of overlap, Cλ, which is calculated using numerical (percent number) and mass (percent dry weight) data from stomach analyses. Values of Cλ calculated from numerical data show a moderate degree of food overlap. Values of Cλ calculated from mass data, however, show less overlap. It is concluded that on a basis of diet biomass, these two species of salmon fry effectively partition food resources.