First winter energy allocation in juvenile sablefish Anoplopoma fimbria, a fast growing marine piscivore

Abstract

Understanding how energy allocation changes with ontogeny can provide insights about survival bottlenecks during early life stages for marine fishes. Energy allocation in juvenile fish before and during their critical first winter differs among species based on life history and foraging characteristics. To improve understanding of energy-size relationships in marine fish, we examined seasonal energy allocation in sablefish Anoplopoma fimbria, a species with unusually fast growth rates during early life. We assessed seasonal metrics of growth and energy storage in sablefish during their first 2 yr using field collections from 2016-2019. Based on growth rates estimated from length-frequency distributions, sablefish increased rapidly in size during autumn, and growth continued but slowed through their first winter as newly settled young-of-the-year. Mean energy density (ED, kJ g-1) declined over the winter, but total energy (TE, kJ ind.-1) increased significantly between October and March, reflecting positive overwinter growth. Relationships between energy storage and length were atypical for high-latitude marine fish in that they were steepest in March, indicating that relatively large fish grew during winter with minimal energy depletion, whereas relatively small fish grew but depleted their energy stores. We propose that improved foraging success for large fish may explain this pattern. Our results suggest that sablefish benefit from achieving large sizes prior to winter and support the hypothesis that the first winter can be a survival bottleneck for sablefish. This work informs our understanding of piscivore energy allocation during early life history and our understanding of possible sablefish recruitment drivers.