Length of breeding life of coho salmon (Oncorhynchus kisutch)

Abstract

Since Pacific salmon (Oncorhynchus spp.) die on the breeding grounds after spawning, duration of individual life may affect survival of deposited eggs. In addition, breeding life of both sexes has implications for estimates of size of spawning populations. We therefore examined the contributions of body size, population density, water level, season, and year to length of breeding life in individual coho salmon (O. kisutch). Age 3 breeding males and females lived an average of 9 days (range, 2–30 days), and 2-year-old "jack" males averaged 8 days (range, 2–21 days). Sixteen percent of the variance among age 3 males and 44% of the variance among females could be explained by the variables examined. Density of adults made a significant negative contribution to life-span, while water level, season, and year were insignificant. Body size was the most important variable in explaining breeding life-span, being positively related and accounting for 10% and 36% of the variance in 3-year-old males and females, respectively. In contrast, none of these variables explained the observed variation in jack male breeding life. The differences between the sexes and between 2- and 3-year-old males are consistent with levels of competition on the breeding grounds. We show that the results on individual body size and breeding life span can be used to offset biases in population estimates.