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Pacific Halibut Hippoglossus stenolepis captured in directed commercial longline fisheries in Canada and the USA that are below the legal minimum size for retention must be returned to the sea without incurring additional injury. Estimates of mortality caused by discarding sublegal‐sized fish are included in annual estimates of total mortality from all sources and affect the results of stock assessment and the yield available to fisheries. Currently, an average discard mortality rate (DMR) of 16% is applied to all sublegal‐sized longline discards. These discards consist of fish that suffer injuries ranging from minor to severe. The 16% DMR that is currently applied was derived by averaging injury‐specific DMRs that in turn assume 3.5% mortality of Pacific Halibut that are released to the sea with only minor injuries. The latter has been derived experimentally but only in captivity. Here, we used acceleration‐logging pop‐up archival transmitting tags to infer individual survival outcomes for Pacific Halibut that were released in situ following capture on longline gear. Postrelease behavioral data were evaluated for 75 fish that were at liberty for 2–96 d. Three fish were confidently inferred to have died after periods at liberty of 41–80 d, and another three fish may have died 96 d after release, resulting in minimum and maximum estimated 96‐d postrelease DMRs of 4.2% (range = 0.0–8.7%) and 8.4% (range = 1.7–14.6%), respectively. These ranges are consistent with the currently applied value of 3.5%. However, the observation that no mortalities occurred until after 40 d postrelease departs from the findings of captive studies, in which the majority of capture‐induced mortality occurred within 20 d of release. [ABSTRACT FROM AUTHOR]

The Pacific halibut (Hippoglossus stenolepis) stock in the waters of the exclusive economic zones of Canada and the United States of America has been actively managed by the International Pacific Halibut Commission since its formation in 1923. Fisheries accessing this resource have become increasingly varied over time and among geographical areas, and more than capable of utilizing the entire yield available each year, which has averaged 34,000 mt since 1992. In recent years, 69.5 % of the mortality has come from the directed commercial fishery landings, 15.4 % from non-directed commercial fisheries (legally restricted from retaining any halibut) and 15.1 % from all other sources combined (commercial discards, recreational, subsistence). Understanding the relative effects on the stock and potential yield of allocation among fishery sectors is a high priority for managers and participants in these fisheries. This analysis used the 2019 stock assessment for Pacific halibut and three analytical methods to compare the directed and non-directed commercial fisheries. We found that potential yield to the directed fishery was generally larger than a simple reallocation from non-directed discards (115 % on average), that the rate of exchange is variable over time (range of 86–139 %), and that the effect of the directed commercial fishery on the spawning biomass has also changed over time. We conclude that managers should be aware that no simple 'conversion rate' exists for translating mortality among fisheries that differ appreciably when operating on a stock with dynamic biology. [ABSTRACT FROM AUTHOR]