Exploring Spatial and Temporal Patterns in the Size‐At‐Age of Pacific Halibut in the Gulf of Alaska

ABSTRACT Large changes in Pacific halibut ( Hippoglossus stenolepis ) size‐at‐age across decades have affected available fishery yield and management decisions. Characterizing mechanisms driving variability in size‐at‐age of adult Pacific halibut is challenging due to uncertainty associated with spatial and temporal partitioning of the phenomenon. We explored spatial and temporal changes in size‐at‐age structure of Pacific halibut in the Gulf of Alaska during 1998–2021, and the relationship between spatial patterns in size‐at‐age and diet using δ 13 C and δ 15 N analysis of muscle tissues collected in 2018. Pacific halibut size‐at‐age was spatially and temporally structured across the study area, with distinct regions of persistent anomalously high or low relative size‐at‐age. Further, trophic feeding level varied spatially and diet was related to size‐at‐age. Our results provide important context for investigations of specific mechanisms influencing Pacific halibut size‐at‐age and future research on Pacific halibut ecology. We recommend revisiting fundamental aspects of Pacific halibut biology, sampling methodology, and management practices from this spatiotemporal perspective.