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.
