Energetic status and bioelectrical impedance modeling of Arctic grayling Thymallus arcticus in interior Alaska Rivers

The energetic status of fishes represents energy stored as protein and lipids and reflects the ability of an individual to reproduce, migrate, and transition through life stages, ultimately influencing survival. However, traditional measurement methods, while highly accurate, are time consuming, expensive, and lethal, and nonlethal methods such as condition factor may not adequately characterize energetic status. We collected 161 Arctic grayling (Thymallus arcticus) from four interior Alaska river basins with varying hydrologic regimes during early summer and autumn seasons, and used multiple regression and model selection to evaluate the efficacy of bioelectrical impedance analysis (BIA), a nonlethal condition assessment method, to predict percent dry mass and percent lipid content estimated from proximate analysis. We found that Arctic grayling energetic status varied across seasons, by sex, and fish from sites with spawning runs of Pacific salmon had higher energy content than those from sites without salmon, potentially due to the influence of salmon-derived food subsidies. Electrical measurements explained 82% and 80% of the variability in percent dry mass and percent total lipids, respectively, and top models showed high predictive performance (observed vs. predicted root mean squared error ≤2.2%). Overall, we found the BIA approach to provide rapid, precise, and non-lethal estimates of Arctic grayling body condition. Such an approach may be useful for future work to characterize Arctic grayling bioenergetics and monitor fish condition under a rapidly changing Arctic environment.