Stock-specific variation in the probability of precocious male maturation in hatchery Chinook salmon (Oncorhynchus tshawytscha)

Age of maturation in many salmonid species is phenotypically plastic and dependent on exceeding a genetically set threshold in growth, often described as a probabilistic maturation reaction norm (PMRN). Hatchery supplementation programs for Chinook salmon (Oncorhynchus tshawytscha) in the Pacific Northwest US have been developed to minimize differences between hatchery and wild fish by integrating natural-origin adults into broodstock, potentially affecting PMRNs. We raised fish from 10 Chinook salmon stocks with variable levels of natural-origin integration in a common garden environment to explore potential genetic variation in PMRNs for precocious male maturation as age 2 minijacks. Proportion minijacks varied approximate to 10-fold (0.043 to 0.443) and the PMRN W-P50 (predicted weight at 50% maturation) varied by approximate to 18 g (24.1 to 41.7 g). The propensity for minijack maturation was generally higher in stocks with higher levels of natural-origin integration. These findings demonstrate the effect of genotype by environment interactions on life history of salmonids and the need for stock-specific tailoring of rearing regimes to regulate differences between hatchery and wild fish, when wild fish are used in broodstocks.