PACIFIC HALIBUT BYCATCH IN PACIFIC COD FISHERIES IN THE BERING SEA - AN ANALYSIS TO EVALUATE AREA-TIME MANAGEMENT

Mortality of discarded Pacific halibut bycatch from Pacific cod fisher ies in the Bering Sea leads to significant losses in the halibut setli ne and in the Pacific cod fisheries. The commercial halibut fishery lo ses yield because of catch limit reductions to compensate the resource for lost spawning potential and because halibut killed as bycatch wil l not be available for subsequent harvest, and the cod fisheries may l ose harvest if they reach a bycatch mortality limit before reaching al lowed catch. In this study, significant differences in Pacific halibut bycatch rates and associated yield losses were found among months and areas of the Bering Sea in the longline and trawl fisheries for Pacif ic cod in 1990-1992. Bycatch rates were usually highest in late spring and early summer and in areas close to the Unimak Pass. With the exce ption of 1992, yield loss in the longline fishery was around 1 kg per kg of bycatch mortality, irrespective of where or when bycatch occurre d. In the trawl fishery, loss of halibut yield varied from 1 to 4 kg p er kg of bycatch mortality. Highest halibut net yield losses per tonne of groundfish harvest usually coincided with highest bycatch rates. W hen both fisheries operated in one area, trawl bycatch often imposed h igher yield losses than longline bycatch, despite lower bycatch rates. Bycatch was affected by the strong 1987 halibut year class. Highest b ycatch and yield loss rates occurred in the trawl fishery in 1990 and 1991 when the population was dominated by halibut age-3 and -4, and in the longline fishery in 1992 as fish reached age-5. (C) 1998 Elsevier Science B.V. All rights reserved.