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Photoperiod at emergence regulates early life history plasticity in fall Chinook salmon

Fuhrman, Abby1; Harstad, Deborah1; Larsen, Donald1; Beckman, Brian1

Published Jun 16, 2025 on Dryad. https://doi.org/10.5061/dryad.bzkh189n3

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Abstract

Early life history pathways for Chinook salmon are directly related to environmental variation, which can shift phenotypic traits expressed by a population. Fall Chinook salmon in the upper Columbia River Basin historically timed migration downstream (smolted) as subyearlings, however some wild and hatchery reared fall Chinook salmon also express a successful yearling smolt life history strategy. Previous research suggests that this shift to yearling smoltification represents evolution – a genetic change due to an increase in fitness and improved downstream survival. Alternatively, the shift in smolt timing could be a phenotypically plastic response that optimizes life history traits for current environmental conditions. We raised hatchery-origin fall Chinook salmon from the Umatilla River (Oregon, USA) in a controlled laboratory experiment to explore environmental drivers of early life history. We found smolt timing to be age/size dependent for subyearlings, and photoperiod dependent for yearlings. We found the propensity for precocious male maturation at age-1 (microjack) to be primarily photoperiod dependent and for age-2 (minijack) to be primarily growth dependent. The resulting adaptable life history portfolio may provide this population with some baseline capacity to cope with future environmental change.