Management Briefs: Heritability of Age at Maturity in Steelhead

Brood stock of winter steelhead Oncorhynchus mykiss were selected on the basis of age at maturity. Progeny were sampled as returning adults to determine if age at maturity was heritable. Although overlap was observed, progeny of fish that matured after 2 years at sea (2s) tended to return after 2 years, and progeny of fish that matured after 3 years (3s) tended to return after 3 years. The 3s progeny were significantly longer than 2s progeny in 2 years of return for both sexes. No difference was observed in return rates between groups, possibly suggesting that most steelhead mortality occurs before the second summer in salt water, or there is differential mortality associated with ocean distribution.