COMPETITION BETWEEN JUVENILE PINK (ONCORHYNCHUS-GORBUSCHA) AND CHUM SALMON (ONCORHYNCHUS-KETA) AND ITS EFFECT ON GROWTH AND SURVIVAL

Pink (Oncorhynchus gorbuscha) and chum salmon (Oncorhynchus keta) fry have the potential for significant interactions in estuarine and nearshore waters of the Fraser River. Potential competitive effects were investigated by rearing both species for 60 d from fry emergence in monoculture and five duoculture environments (0, 10, 25, 50, 75, 90, and 100% pink salmon, and 100, 90, 75, 50, 25, 10, and 0% chum salmon, respectively), with the total number of fish in each environment constant. As the relative abundance of chum salmon increased, the mean weight of both pink and chum salmon declined, and reduced phenotypic variation in weight was observed. No marked trends in survival were observed in either species, but there was some indication that pink salmon survival was higher at intermediate relative densities of pink and chum salmon. Pink salmon biomass increased from 0.8 to 1.8%/d depending on the environment, and chum salmon biomass increased from 3.2 to 3.8%/d.