Mate Selection in a Population of Sockeye Salmon (Oncorhynchus nerka) of Mixed Age-groups

Abstract

Anadromous Skeena River sockeye mature and spawn mainly at ages 4₂ and 5₂. Lesser numbers of 3₂, 5₃, and 6₃ and 6₄ fish, and non-anadromous kokanee, may spawn in the same stream. Mate selection by the different types was studied by observing salmon of known length and using the relationship found between length and age in dead, spawned fish.Fish of all lengths tended to mate with similar sized fish. Small males were less successful in holding mates than were large males because they could not successfully defend redds against larger intruders. Small males spent more time alone than large ones and frequently lay in groups behind mating pairs. The term "satellite male" is used in describing the behaviour. Small females mated with large males but spent more time alone than did large females.The genetic implications of mating within age-groups are considered.