FISHERY BULLETIN: VOL. 75. NO. 4 



the offshore region, splitting the catch north and 

 south of lat. 35°N showed that the catches first 

 developed south of lat. 35°N and then moved 

 north. By the fourth period (20 to 29 June), the 

 small-size modal group composed almost the en- 

 tire catch south of lat. 35°N and offshore of long. 

 135°W. 



Several conclusions are evident from these tem- 

 poral and areal changes in size composition. While 

 catches persisted for up to 4 wk within a 2° by 4° 

 quadrangle of latitude and longitude in the 

 offshore region, changing patterns of size composi- 

 tion suggest that albacore were moving through 

 the region within a period of 10 days or less and 

 that the size groups migrated somewhat indepen- 

 dently. The mid-size group, which composes the 

 major portion of the U.S. fishery, led other size 

 groups by 10 or more days. Also, the sequence of 

 compositional changes of each size group and the 

 geographic differences suggest that the migration 

 from the offshore region to the nearshore fishery 

 takes about 20 days or more; at least it did in 1972. 



The 1972 catch data were chosen for examina- 

 tion of spatial and temporal changes in size com- 

 position because each of the size groups was well 

 represented in the survey catches and all phases of 

 the migration into the fishery are evident, includ- 

 ing commencement of the fishery, by the comple- 

 tion of the survey. In 1973 the fishery started late, 

 weeks after the survey, and in 1974 the patterns 

 were less distinct, apparently in response to weak 

 oceanic frontal conditions. 



DISCUSSION 



Association of Albacore Distribution 

 With Oceanic Frontal Regions 



The commercial fisheries on North Pacific alba- 

 core and the migration of albacore among these 

 fisheries have frequently been associated with 

 oceanic frontal regions in the western Pacific 

 (Yamanakaetal. 1969; Uda 1973; other works), in 

 the central North Pacific (Shomura and Otsu 

 1956; McGary et al. 1961), and in coastal upwell- 

 ing regions (Pearcy and Mueller 1970; Panshin 

 1971; Laurs 1973; Laurs et al. 1977). 



Results of our study provide evidence for the 

 continuity of the association of albacore distribu- 

 tion with the Transition Zone and frontal bound- 

 aries into the eastern North Pacific. Catches made 

 by the AFRF charter fishing vessels and the re- 

 search vessel during each of the three surveys 



demonstrate that albacore are distributed mainly 

 within the Transition Zone and usually are absent 

 (or unavailable) in water masses to the north and 

 south. Furthermore, our work strengthens the 

 general concept that the distribution and relative 

 abundance of large, highly migratory fish may be 

 markedly influenced by oceanic frontal features. 

 Other studies usually have had to rely on mean 

 ocean conditions and/or statistically averaged 

 fishery data, whereas our fishery and oceano- 

 graphic data were collected concurrently during 

 several surveys, and the amounts of fishing effort, 

 fish catch, and oceanographic data were substan- 

 tial. 



Relative Abundance of Albacore in the 

 Eastern Sector of the Transition Zone 



We have found centers of high relative abun- 

 dance of albacore in June within the eastern sector 

 of the Transition Zone and often close to its frontal 

 boundaries. Annual and intra-annual areal varia- 

 tions in relative abundance of albacore were ob- 

 served and appeared to be related to development 

 of the frontal boundaries of the Transition Zone. 

 When the Subarctic and Subtropic fronts were 

 strongly developed, areas of high relative abun- 

 dance developed within relatively narrow bands 

 in the Transition Zone and persisted for several 

 weeks. When the Transition Zone was broader and 

 the fronts were poorly developed, centers of high 

 relative abundance were found over a larger area 

 within the Transition Zone and did not persist for 

 more than several days in any one location. 



Based on scouting results from several research 

 surveys, it appears that the timing and the loca- 

 tion of fishing effort may be critical in locating 

 centers of high relative abundance of fish in the 

 eastern sector of the Transition Zone. In 1973, 

 charter vessels first found a center of high relative 

 abundance on 4 June near lat. 34°N, long. 140°W 

 in Transition Zone waters. For several weeks prior 

 to this finding, the AFRF charter vessels had made 

 only scattered catches while scouting in and about 

 this same area. Thus, it seems that the center of 

 high relative abundance appeared in a surge 

 within the first week of June. In 1955, an albacore 

 survey cruise by a single U.S. Bureau of Commer- 

 cial Fisheries (BCF) research vessel (Hugh M. 

 Smith) scouted this area in late May and early 

 June (Graham 1957). Seven longline sets and 

 trol ling conducted between lat. 4 1 ° and 28 °N along 

 long. 139°W resulted in only a single albacore 



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