Attraction of Migrating Adult Sockeye Salmon to Conspecifics in the Absence of Imprinted Cues

Pacific salmon (Oncorhynchus spp.) use olfactory cues to navigate upstream during the spawning migration. Two main sources of olfactory cues have been identified—imprinted natal cues and conspecific odors (pheromones)—although the relative importance of these cues is unresolved. We tested the response of migratory adult sockeye salmon (O. nerka) to conspecific odors in the presence of, and in the absence of, imprinted natal cues. The results indicate that sockeye salmon are attracted to conspecifics when imprinted natal cues are absent, but not when they are present. This suggests that pheromones may provide a directional cue that is secondary to the primary cue of imprinted chemicals. There are several potential benefits to this method of navigation that could result in increased reproductive success of stray migrants, which could promote dispersal and increase genetic diversity within populations.