Rockfish Bycatch: Spatial Analysis Using Observer Data in the Aleutian Islands and Bering Sea
Authors: Charles Steinback & Sarah Klain, Ecotrust
June 8, 2005
The intended purpose of this report is to help AMCC begin location-specific discussions with regional and local stakeholders about rockfish conservation in the Bering Sea and Aleutian Islands. Within these regions, rockfish are frequently caught in large quantities as bycatch when groundfish fishermen are targeting species such as Atka mackerel, Pacific cod, and pollock. This persistent bycatch issue, particularly among trawlers, is often linked to habitat destruction and detrimental impacts on the marine food web. In this report, an alternative methodology is presented for using NMFS groundfish observer data to identify areas (10 km x 10 km blocks) within each region where bycatch of specific rockfish species has occurred from 1990-2002. These areas are ranked in priority according to various criteria that are explained in our methodology. Decisions regarding bycatch reduction can be better informed with this spatially explicit information.
In the following section, we present four scenarios representing areas encompassing various percentages of the total rockfish catch derived from observed tows. The methodology combines pelagic and non-pelagic trawl data summarized by the prevalent northern rockfish, a rockfish species that is caught and discarded as bycatch more than any other rockfish in the Aleutian Islands and Bering Sea. Northern rockfish is second only to Pacific ocean perch as the most abundant Alaskan rockfish (AFSC, 2004). It should also be noted that as of 1997, the National Marine Fisheries Service prohibited targeted fishing for this species in the Aleutian Islands and it has historically only been caught as bycatch in the Bering Sea (Clausen and Heifetz, 2002).
The catch data used in the analysis, observer data, does not encompass the total catch in the groundfish fishery in the Aleutian Islands and Bering Sea. Observer data only includes catch quantities from observed vessels that conduct sampled trawl tows and longline hauls. Not all vessels are observed and not all trawl tows and longline hauls are sampled. In addition, NMFS classifies observer data as confidential when less than three boats are observed catching the same target species in a fishing block. Despite these limitations, observer data is the most detailed rockfish bycatch data publicly available that can be analyzed spatially.
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