Associations between stream habitat and energetic condition in juvenile coho salmon ( Oncorhynchus kisutch )

Spatiotemporal variation in habitat quality and quantity impacts individual fish energetics by influencing growth, energy storage, and survival, ultimately shaping population dynamics. However, few studies have explicitly linked individual energetic condition to habitat variation across both space and time. In two studies, we investigated the influence of variation in freshwater habitat characteristics (September 2020) and season (July 2022 to April 2023) on both physiological (e.g., percent lipid, percent protein, and energy density) and morphological (e.g., relative condition factor) metrics of juvenile coho salmon energetic condition in interior British Columbia, Canada. Physiological metrics were associated with spatial and temporal variation in habitat. Among sites, higher percent lipid was associated with lower water temperature and higher energy density with elevated stream nutrient concentrations. Across seasons, energetic condition declined over both summer and winter. Post-winter percent lipid and energy density values converged on proposed survival thresholds. Collectively, this research demonstrates the utility of physiological energetic condition metrics as tools for quantifying how habitat changes affect juvenile salmon energetic condition, improving evaluations of habitat protection and restoration actions.