Protandry models and their application to salmon

Mating systems characterized by restricted breeding seasons, male polygamy, and female monogamy are common among animals. In such systems (e.g., butterflies), the earlier emergence of males than females to breeding areas (protandry) is a typical phenological pattern. Protandry likely results from a timing strategy that maximizes mating opportunities by males. In Pacific salmon (Oncorhynchus spp.), males typically arrive at the spawning grounds in advance of females. Using arrival-timing models, I found that under the mate-opportunity hypothesis, the mating system of salmon favors protandry. Protandry is predicted under a range of competitive scenarios, and the degree of protandry is especially sensitive to the duration of male spawning activity. Greater protandry is expected with increasing population sex ratio (i.e., more males) when there is mate guarding, but lower protandry is expected with increasing population sex ratio when interference competition among males reduces male longevity. The timing of unequal competitors is expected to be similar, but among years, protandry may be less variable in the better competitor. Copyright 2002.