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NOAA Technical Memorandum NMFS-AFSC-265

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Estimation of bycatch in the unobserved Pacific halibut fishery off Alaska


The commercial fishing fleet targeting Pacific halibut (Hippoglossus stenolepis) was unobserved until 2013. Prior to that, catches of non-halibut species (bycatch) were not accounted for unless the bycatch was landed. State of Alaska and Federal fishery managers and scientists have long recognized the need for bycatch estimation in this fishery. At-sea data collection (i.e., observers) was not authorized until 2013 with the implementation of Amendment 76 to the Fishery Management Plan for Groundfish Fisheries in the Gulf of Alaska and Amendment 86 to the Fishery Management Plan for Groundfish Fisheries in the Bering Sea/Aleutian Island Area.

Accounting for bycatch in the Pacific halibut fishery is also a requirement under the guidelines to National Standard 1 of the Magnuson-Stevens Fishery Conservation and Management Act. We examined six methods of estimating bycatch that combined data from the International Pacific Halibut Commission’s (IPHC) annual longline survey and commercial catch per unit effort (CPUE). Results suggest that an approach which proportionally weights the survey data is the most appropriate method to treat the survey data to reflect commercial fishing and that using CPUE based on numbers of fish per hook is more appropriate than other methods proposed. However, all methods rely on the assumption that the catch characteristics of the IPHC survey are statistically similar to those occurring in the commercial fishery.

The purpose of this project was not to determine how these catch estimates should be incorporated into the assessment and no management advice is provided in this document. There are a number of caveats to be considered when using the catch estimates and assessment authors are recommended to be aware of those caveats prior to using the estimates.

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