| Summary: | Olfactory cues can provide many forms of information about an animal’s environment. For some migratory species, these cues guide migrants towards foraging or reproductive grounds. Pacific salmon (Oncorhynchus spp.) use olfactory cues to locate their natal sites during the spawning migration. The objective of this thesis was to further our understanding of the olfactory-mediated movements of Pacific salmon as they return to their home streams to spawn. Through a synthesis of past studies on olfactory navigation in anadromous fish, I identified critical knowledge gaps and future directions for research. Drawing from two long-standing hypotheses that seek to explain how salmonids navigate to their natal sites, I developed a new hypothesis that suggests salmonids use imprinted odours of their natal water as primary directional cues, pheromones as secondary cues, and non-olfactory environmental information as tertiary cues. One of the major implications of this hypothesis is that salmonids that have strayed from their natal migratory route might use pheromones to locate suitable spawning habitat. Using samples I collected from wild adult sockeye salmon (O. nerka), I found increased expression of potential pheromone receptors in strays. I also found that sockeye salmon are behaviourally attracted to the odour of conspecifics when imprinted natal cues are absent, as would be the case for a stray salmon, but not when the imprinted cues are present. Conspecific odours are not always attractive during the migration however, as I found sockeye salmon avoided the odour of conspecifics that were subjected to a handling event, suggesting these fish release chemical disturbance cues when stressed. Pink salmon (O. gorbuscha) did not avoid the odours of disturbed conspecifics, which might relate to species-level differences in life history. Finally, I analyzed the influence of altered flow composition resulting from hydroelectric developments on olfactory navigation in sockeye and pink salmon. Alterations can disorient salmon as they swim upstream, and the results provide guidelines for managers to minimize such disorientation in this river system. The findings of my thesis contribute to our understanding of the olfactory process in salmonids, and point to future research directions in the field of salmonid homing. === Forestry, Faculty of === Graduate
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