Stock Differences in Growth, Smolting, and Early Male Maturation in Hatchery Spring Chinook Salmon: a Common‐Garden Experiment

Abstract

AbstractHatchery spring Chinook Salmon Oncorhynchus tshawytscha from Parkdale Hatchery on the Hood River, Oregon, and Carson National Fish Hatchery (CNFH) on the Wind River, Washington, were reared under a common‐garden experimental regime at CNFH over three consecutive brood years (2008–2010) to assess the effects of stock on smoltification and early male maturation. Rearing groups were monitored for size, percent solid (a surrogate for whole‐body lipid), gill Na+,K+‐ATPase activity, and rate of precocious maturation in males (i.e., age‐2 minijack rate). Despite rearing of the stocks under identical conditions, the out‐of‐basin Hood River stock was significantly smaller throughout the study and at release as smolts, had lower whole‐body lipid at release, and had lower gill Na+,K+‐ATPase activity at release than the Carson stock; furthermore, the Hood River stock exhibited much higher mean minijack rates than the Carson stock (45% versus 23% of males). Using logistic regression, we demonstrated that the threshold size for initiation of early male maturation was significantly lower for the Hood River stock than for the Carson stock, suggesting a genetic basis for this life history difference. The present study highlights the importance of understanding how specific genotypes may respond differently to the unique environmental conditions in a given hatchery environment. These differences may in turn influence physiological and life history pathways that affect smolt‐to‐adult return rates and the demography of returning adults.