The commercial size limit for the Pacific halibut fishery off Alaska and its relationship to observer-derived estimates of at-sea discard

Halibut fisheries off Alaska operate under federal regulations requiring halibut intended for commercial sale be at least 32 inches (~ 81 cm) in total length. The minimum size limit complicates estimation of halibut discard due to the limited amount of disposition-specific data collected by observers available to calculate mean weights. Observers collect fish weights that are used to estimate the mean weight per fish from the unsorted (retained and discarded) catch. They also collect counts of retained fish to estimate the percent of the catch retained. The calculation of the mean weight per fish using observer data may overestimate the mean weight of discarded fish and underestimate the weight of retained fish. While estimates of retained catch are based on landings data and thus are not biased, the haul-specific estimates of at-sea discards of halibut in the halibut fishery are biased. This analysis assessed the impact of bias on the total discard estimates and proposes an adjustment to mitigate the bias. 2022 NMFS (National Marine Fisheries Service) AFSC (Alaska Fisheries Science Center) AKR (Alaska Region) Submitted https://doi.org/10.25923/8xhp-7q20 Public Domain 2035