Interpopulation variation in thermal physiology among seasonal runs of Chinook salmon

Conservation of species facing environmental change requires an understanding interpopulation physiological variation. However, data are often scarce and therefore pooled across populations species, erasing potentially important variability between populations. Interpopulation variation in thermal physiology has been observed within the Salmonidae family, although it not associated with seasonally distinct migratory phenotypes (i.e., seasonal runs). To resolve whether is life-history strategy, we acclimated four Sacramento River juvenile Chinook salmon ( Oncorhynchus tshawytscha) (Coleman fall-run, Feather spring-run, winter-run) exhibiting different (fall-, spring-, winter-run), at 11, 16, 20 °C assessed growth rate, critical maxima, temperature-dependent metabolic traits. We identified population differences parameters measured found compelling evidence that critically endangered endemic winter-run exhibits its early-migration strategy. Acclimation to warm temperatures limited capacity salmon, highlighting risk future warming this population.