A Spatially-Explicit Stock Assessment Model for North Pacific Sablefish: Movement and the Implications for Management

Sablefish (Anaplopoma fimbria) is a highly mobile groundfish in Alaska, and three decades of tag-recapture data have been collected and analyzed to estimate age- and length-based movement rates. Using these estimated rates, we developed a spatially-explicit stock assessment model examining sablefish abundance in three regions: the Bering Sea/Aleutian Islands/Western Gulf of Alaska, the Central Gulf of Alaska, and the Eastern Gulf of Alaska.  Currently, the fixed gear fishery in each of these regions is managed by individual fishing quotas (IFQs), where an estimated total ABC for Alaska is apportioned to each region’s quota holders based on spatial biomass estimates from fishery and survey abundance indices. We compared sablefish abundance from the spatial model combined over the three regions to a single-area model that ignores movement. The spatial model and the single-area model produce similar estimates of total and spawning biomass. However, spatial model area ABCs differ from area ABCs from the single-area model, by accounting for sablefish movement. In addition, results from the spatial model with movement yielded different distribution of ABCs than the current Alaska assessment and the spatial model with no movement. This has implications for managers and fishermen, because IFQs are assigned to a specific management area.