We test the hypothesis that Colorado River flow is important in providing nursery habitat for the Gulf corvina (Cynoscion othonopterus), a commercially valuable and endemic fish in the upper Gulf of California. We use oxygen isotopes in otoliths to determine when these fish inhabit isotopically different bodies of water (Gulf of California versus the Colorado Estuary). The δ18O values in the natal otoliths of C. othonopterus, significantly more negative than can be predicted by temperature alone, provide evidence that this species uses the brackish habitats created by flow of the Colorado River. A significant log-linear relationship between the natal δ18O values and the cumulative flow of the Colorado River during natal development confirms use of brackish habitat in years that the Colorado River water reached the Gulf. Natal δ18O values indicate that C. othonopterus seek out estuarine habitats with salinities between 26‰ and 38‰. Reduction in Colorado River flow since the construction of upstream dams has reduced the size of nursery habitat for C. othonopterus. Our results support the hypothesis that declines in commercial landings can be at least partially attributed to reduced river flow. Increased flow would increase nursery habitat and likely benefit recruitment.

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Relationships among somatic growth, climate, and fisheries production are poorly understood for coastal fishes in the Gulf of California (GoC), Mexico, but may serve as an adaptive management tool to set precautionary harvest limits for overfished, data‐limited stocks. We explored linkages among the Multivariate ENSO Index (MEI), regional sea surface temperatures (SST), otolith growth chronologies of juveniles and adults, and annual landings in the Gulf corvina (Cynoscion othonopterus), an overexploited marine fish that supports the most important coastal finfish fishery in the northern GoC. Both MEI and SST were positively correlated with corvina landings five years later (peak age at capture), indicating that climate conditions at birth were a reliable predictor of future fisheries production. Juvenile growth rate covaried with both MEI and SST, confirming the influence of climate during early life history. There was no significant covariance from year to year in adult growth rate, but there was a significant cohort effect that positively correlated with MEI and SST, suggesting that climate conditions early in life exert lasting impacts that persist through adulthood. Differences in climate–growth relationships between juveniles versus adults were attributed to differences in the geographic distributions of the two life stages. Overall, we conclude that climate variability influences the future harvestable biomass of the corvina fishery via impacts on juvenile growth, and thus survivorship. Systematic monitoring of the corvina population, its fishery, and the biophysical components of the GoC environment must continue to improve our understanding of these climate‐driven processes and the management of the fishery.