A heatwave confounds post-restoration recovery assessment and reveals limited thermal refugial function of the tailrace: demographic and physiological insights from a cold-stenothermic fish population

This dataset contains the raw data from a field study investigating the within-population responses of the cold-stenothermic wrinklehead sculpin (Cottus nozawae) to dam flow diversion cessation and a subsequent heatwave in the Toyohira River, Hokkaido, Japan. It comprises two datasets: (1) FishBiometrics_Spatiotemporal_Wu et al., 20260706, containing individual fish biometric data (sampling information, total length, and body weight); and (2) PopulationAgeStructure_HabitatEnv_Wu et al., 20260709, containing replicate-level age-class abundance, sampling area, habitat characteristics, and environmental variables collected during four sampling occasions between October 2022 and October 2024. The datasets were used to evaluate age-specific environmental responses and spatiotemporal variation in demographic structure and body condition under interacting hydrological and climatic stressors.