Effect of migration on lost yield, lost spawning biomass, and lost egg production due to U32 bycatch and U32 wastage of Pacifi c halibut

During the last 60 years, annual catches in the directed commercial Pacifi c halibut fi shery have ranged from about 20 million pounds to about 75 million pounds, whereas bycatch mortality of halibut in non-directed fi sheries has averaged about 14 million pounds per year. Treatment of bycatch in IPHC management has changed over time from different forms of explicit area-specifi c quota deductions to the implementation of the current method, which is based on a harvest rate adjustment, in the late 1990s. The current method deducts O32 bycatch from area-specifi c quotas and incorporates U32 bycatch in the determination of the target harvest rate. At that time, migration modeling of U32 bycatch indicated that the impact of U32 bycatch was largely confi ned to the area where the bycatch was taken. However, this approach assumed that ontogenetic halibut migration ceased by the time halibut became available to commercial gear, an assumption that has been refuted by a recent extensive tagging program. Here we report preliminary results on the impact of U32 bycatch and U32 wastage on lost yield (LY), lost spawning biomass (LSBio), and lost egg production (LE) in light of the improved understanding of halibut migration. Preliminary results suggest that coastwide impacts on LY, LSBio and LE are similar with or without accounting for migration of U32 bycatch and U32 wastage. However, area specifi c impacts on LY, LSBio, and LE vary by area when accounting for migration. The effect of migration is to decrease impacts of U32 bycatch and U32 wastage on Area 4 and to increase impacts on other areas, particularly Area 2. Much of the impact of U32 bycatch is determined to be on areas outside of where the bycatch was taken. In contrast, most of the impacts of U32 wastage are determined to be from local wastage.