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NOAA Technical Memorandum NMFS-AFSC-260

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North Pacific marine mammal bycatch estimation methodology and results, 2007-2011


Analyses of North Pacific marine mammal bycatch data for the period 1989-2006 have been made by Perez (2003, 2006, Unpubl.) based on Structured Query Language scripts. A change in the structure of the Oracle database maintained by the Fisheries Monitoring and Analysis (FMA) Division of the Alaska Fisheries Science Center in 2008 required that analysis programs be rewritten. The present analysis, for the period 2007-2011, was undertaken using the R programming language (R Core Team, 2012). Bycatch estimates were calculated for each of 23 groundfish trawl, longline, and pot fisheries in Alaska using the FMA observer data and the total fishery data from the Catch Accounting System of the Alaska Regional Office of the National Marine Fisheries Service. Fisheries were determined by the target species, gear type, and area. The weight of all groundfish caught in a haul was used as a measure of effort. The total number of hauls was unknown for each fishery. The ratio of sampled groundfish weight to number of sampled hauls was assumed to be equal to the ratio of total groundfish weight for the fishery to the total number of hauls in the fishery. The observed bycatch of all marine mammal species for the years 2007-2011 was 16, 38, 20, 23 and 32, respectively. An additional 12 marine mammal mortalities were observed but were not used to estimate total marine mammal mortality because they occurred in hauls with unknown effort. The estimated bycatch of all marine mammals for these years was 31.8, 42.9, 21.1, 28.6 and 38.4, respectively. The following marine mammal species were bycaught during 2007-2011: bearded seal, harbor seal, northern elephant seal, northern fur seal, Steller (northern) sea lion, ribbon seal, ringed seal, spotted seal (larga seal), unidentified pinniped, walrus, Dall's porpoise, gray whale, harbor porpoise, humpback whale, killer whale and sperm whale. Annual bycatch (killed or seriously injured) estimates were calculated for each marine mammal stock in each fishery for the 5 year period. These estimates are used to assess and manage marine mammal stocks and for classification of commercial fisheries.

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