Behavior and Breeding Success of Wild and First‐Generation Hatchery Male Spring Chinook Salmon Spawning in an Artificial Stream

Spring Chinook salmon Oncorhynchus tshawytscha native to the upper Yakima River, Washington, were placed into an artificial stream to evaluate the effect of a single generation of hatchery culture on their spawning behavior and ability to produce offspring. From 2001 to 2005, seven independent test groups containing wild and hatchery fish were placed into the stream. The effects of body weight, spawning ground longevity, attack frequency, social dominance, courting frequency, and mate number on breeding success in hatchery and wild males were evaluated. Male breeding success increased with body weight, while spawning ground longevity was negatively associated with breeding success. Although important, body weight had a lesser effect on male breeding success than did social dominance or attack frequency. Males with high attack and courting frequencies produced the most progeny; of the traits examined, the number of female spawning partners explained the greatest amount of variation (average r2 = 80%) in male breeding success. Differences in male agonism due to male origin were found. Wild males exhibited higher attack rates and greater social dominance than did hatchery males. However, the observed inequalities in agonism and dominance appeared to be largely caused by differences in body weight between the two types of males: wild males were, on average, 9% heavier than hatchery males. Wild and hatchery males did not differ in the frequency of courting behaviors or in the number of mates. Pedigree analyses based on DNA showed that hatchery and wild males had comparable breeding success values. Consequently, a single generation of hatchery exposure appeared to have a low effect on spring Chinook salmon male breeding success in our experimental setting.