Attraction of migrating adult sockeye salmon to conspecifics in the absence of natal chemical cues

Directed animal movement, which drives behaviors such as natal philopatry or dispersal, is guided by the input of sensory information. Anadromous salmonids are philopatric (they return to their natal habitat to reproduce), and their upstream movements during the spawning migration are directed by olfactory cues. Two main sources of olfactory cues have been identified—imprinted natal cues and pheromones—although the relative importance of these cues is unresolved. We tested the response of migratory adult sockeye salmon (Oncorhynchus 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. The finding follows the hierarchical navigation hypothesis and is supported by previous findings in salmonid research. There are several potential benefits to this method of navigation that could increase the reproductive success of stray migrants, which could promote dispersal and increase genetic diversity within populations.