Steelhead (the anadromous form of Rainbow Trout Oncorhynchus mykiss) exhibit a complex life history that is described by variable freshwater and ocean residency and maturation schedules. This diversity confers resilience but complicates their monitoring and management. The Situk River in Southeast Alaska has the longest running set of biological data and scale samples for steelhead in the state, and it is of particular interest because it supports the largest known population of steelhead in Alaska and is free of hatchery influence. We used a retrospective analysis of scales that were collected from 525 individuals over 11 years (1999–2012) to examine the relationships among freshwater growth, early ocean growth, and life history in a mixed‐effects modeling framework. Specifically, we examined the relationships among annual growth stanzas and adult length and we determined how age at maturity varied by sex and growth history while allowing these relationships to vary randomly among calendar years of growth. Within individuals, freshwater and first ocean‐year growth were positively correlated, while second ocean‐year growth was negatively correlated with earlier growth stanzas. Early‐maturing steelhead (returning after two ocean years) grew more quickly during their first ocean year, and they then grew more slowly during their second ocean year and attained smaller adult length than did later‐maturing steelhead (those that returned after three ocean years). Second ocean‐year growth was more variable than first ocean‐year growth and adult length were. Males tended to mature earlier than females did, and later‐maturing males attained larger freshwater growth than their earlier‐maturing male counterparts did and grew larger in overall length than did females. Our analyses identified divergent growth trajectories that were associated with age at maturity that began in freshwater periods but were most pronounced during early ocean residency. We found retrospective scale‐growth analysis to be a useful tool for better understanding the connections between ocean growth and demography in this important sport fish.

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