Incidental catches of salmonids in the 1991 North Pacific squid driftnet fisheries

Abstract

In 1991, the National Marine Fisheries Service, as mandated by the U.S. Driftnet Impact Monitoring, Assessment, and Control Act of 1987 and U.S. Public Law 101-627, developed methods to estimate the incidental catches (bycatch) of salmonids in the North Pacific squid driftnet fisheries of Japan, the Republic of Korea (ROK), and Taiwan. Two analytical approaches were used for the Japanese fishery: 1) simple expansion of average observed vessel-trip bycatch for total trips by the fleet, and 2) expansion of kernel-smoothed bycatch rates of monitored fishing effort among time and area strata to account for total fishing effort expended within strata. Bootstrap resampling was used to determine the reliability of all estimates. Total salmonid bycatch in the 1991 Japanese squid driftnet fishery was estimated to be 43,700 (vessel-trip method) or 32,100 fish (kernel technique). With an additional 6,000 (vessel-trip method) or 4,400 (kernel technique) salmon estimated to have dropped out of the driftnets during retrieval, total salmonid mortality (bycatch + dropouts) was estimated to be 49,700 (vessel-trip method) or 36,500 fish (kernel technique). Total salmonid bycatch in the squid driftnet fishery of the Republic of Korea was estimated at 13,500 fish using two-stage expansion. First, observed bycatch rate of each monitored time and area stratum was expanded by stratum effort to estimate the stratum bycatch. Second, the sum of these estimated bycatches for monitored strata was expanded for effort in unmonitored strata. Dropouts were estimated at 3,100 fish for a total mortality of 16,600 salmonids. Only 10 salmonids were observed in the squid driftnet fishery of Taiwan, and the total salmonid bycatch was evidently small. The salmonid bycatch in these legal squid driftnet fisheries was minor compared with catches of Alaskan coastal fisheries in 1991, as it was in 1989 (when U.S. monitoring began) and in 1990. The 1991 salmonid bycatch was also small compared with estimates of annual illegal catches of salmonids from the North Pacific Ocean in recent years.


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