Analysis of Marine Mammal Bycatch Data From the Trawl, Longline, and Pot Groundfish Fisheries of Alaska,1998-2004, Defined by Geographic Area, Gear Type, and Catch Target Groundfish Species

Abstract

In 2003, Perez (2003) reported on an analysis of marine mammal incidental take data in federally managed groundfish fisheries in Alaska from 1989 to 2001. At that time, these fisheries were defined in the List of Fisheries by geographic area and gear type. In recent years, fishery definitions have changed to also specify target species. This report presents a re-analysis of the marine mammal incidental take data for the trawl, longline, and pot fishing gear from 1998 to 2001, separated by target species, and includes previously unpublished data from 2002 to 2004. Rates and variance of bycatch (incidental take mortalities and serious injuries) were calculated by stratified ratio estimates, using the sum of the marine mammals observed killed or seriously injured (including trailing gear) by fishing operations divided by the sum of the observed tonnage of fish catch in monitored hauls from the NORPAC database of the North Pacific Groundfish Observer Program, Alaska Fisheries Science Center. Estimates of total bycatch for each of 22 groundfish trawl, longline, and pot fisheries (based on intended catch target groundfish species) in Alaska were calculated using the total fishery data from the Catch Accounting System (CAS; successor to the Blend) database of the NMFS Alaska Regional Office (AKR). The target groundfish species for all NORPAC hauls in the CAS were estimated by the AKR using a sequential, hierarchical combination of a three-step process. In this study, NORPAC hauls were matched to their counterparts in the CAS by vessel, gear type, area, processing sector, and trip target date. Sixteen species of marine mammals were observed incidentally killed or injured by the groundfish fisheries in the U.S. Exclusive Economic Zone off Alaska during 1998-2004. The 22 trawl, longline and pot groundfish fisheries of Alaska were estimated to have incidentally taken 189 marine mammals during 1998-2004. Average annual rates of take for each marine mammal species and for each target fishery were calculated for the most recent 5 years (2000-2004) for use in the List of Fisheries evaluation.

Based on preliminary analyses of depredation rates of marine mammals on groundfish catch, the estimated average annual impact on the total longline fishery groundfish catch in sets subjected to marine mammal depredation ranged from 0.1% (by weight) in the Gulf of Alaska (GOA) Pacific cod longline fishery to 22.3% in the GOA rockfish longline fishery. The average annual depredation impact (but not the quantity of fish actually consumed) by marine mammals on the combined longline fisheries was 2.2% of the total fishery groundfish catch during 1998-2004.


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