Revised estimates of the bycatch of herring in 1989 Bering Sea trawl fisheries. Regional Information Report 5J90-01. Alaska Department of Fish and Game, Juneau, Alaska.

Abstract

Foreign fishing records and scale pattern analyses demonstrate that herring stocks that spawn in Bristol Bay migrate clockwise around Bristol Bay, arriving on the wintering grounds north and west of the Pribilofs in September. Herring stocks that spawn north of Bristol Bay appear to move more directly offshore after spawning. It is uncertain whether herring stocks from Kuskokwim Bay to Nelson Island move directly offshore or follow a clockwise migratory pattern 1 i ke Bristol Bay stocks. Based on prior joint venture (JV) and foreign records, only 1989 Pacific cod and pollock trawl fisheries that occurred along the herring migration route had the potential to take significant amounts of herring. Yellowfin sole fisheries did not occur near herring spawning grounds during the herring spawning period in 1989. Herring bycatch by JV fisheries in 1989 was estimated to be 2,588 tonnes. Most of the JV bycatch occurred in pollock fisheries in National Marine Fisheries Service (NMFS) reporting areas 521 and 522 (north and west of the Pribilofs) in the fall. The most comprehensive source of herring bycatch for domestic fisheries for 1989 was obtained by applying average 1983-88 foreign and JV observer bycatch rates by 1/2" latitude by longitude area by month to 1989 fish ticket catches by 1/2" latitude by lo longitude by month. Using this method, herring bycatch was estimated to be 559 tonnes for domestic Pacific cod fisheries, 1,808 tonnes for pollock bottom trawl fisheries and 346 tonnes for pol lock midwater trawl fisheries. A1 though observer bycatch rates were computed based on the total catch, for ease of computation observer bycatch rates were applied only to the retained catch of the single target species in the fish ticket catch. Because of this, herring bycatch was underestimated by this method. The degree of was underestimation greater for bottom trawl data than for midwater trawl data, because there are usually more species in bottom trawl catches. Landed discard reported on fish tickets and actual domestic observer catch reports for 1 imited areas were also used to estimate herring bycatch in 1989 domestic trawl fisheries. These estimates were roughly comparable to the herring bycatch computed by applying 1983-88 average observer bycatch rates to the 1989 fish ticket catches. However, landed discard herring bycatch rates also underestimate herring bycatch when at-sea sorting occurs or when trawl cod-ends are released because they contain significant numbers of prohibited species. Total herring bycatch estimated for JV and domestic fisheries for 1989 ranged from 4,521-5,301 tonnes. Because several of the methods used underestimate herring bycatch rates, these estimates represent the lower bound of the actual 1989 herring bycatch. Bering Sea herring stocks are declining and are projected to decline below threshold 1 eve1 s where commercia1 fisheries are a1 1 owed at Nelson Island and Nunivak Island in 1990. If no recruitment is observed in 1990, the Togiak stock will likely be below its threshold in 1991. Because herring stocks have declined while the bycatch of herring has increased, herring bycatch exploitation rates have increased from less than 2% in 1983 to 4%-5% in 1989, and are projected to increase further in 1990. When trawl herring bycatch is considered, the maximum allowable herring exploitation rates under the Alaska Board of Fisheries herring harvest policy are being exceeded.
Subsistence utilization of herring resources is high in some communities of western Alaska, particularly at Nelson Island. Although declines in herring abundance projected for 1990 would not result in subsistence closures for 1990, subsistence availability may be reduced and further declines in the resource could force reductions of subsistence harvests. Western Alaska communities experienced severe difficulties in harvesting herring for subsistence purposes during herring stock declines in the 1970s. Fish ticket records of catch by 1/2" latitude by 1" longitude by date of landing allow relatively detailed distributions of fishing effort to be examined. Combining these fish ticket records with foreign and JV observer herring bycatch records in the same area and time strata could allow detailed examination of alternative herring bycatch control measures. Herring bycatch control measures were last examined when the draft Bering Sea herring fishery management plan was submitted by the NPFMC to the Secretary of Commerce in November 1983. Since that time, a considerable amount of new data has become available for herring bycatch analysis.