NORTH 



AMERICAN 



FISHERY 



RECRUITS 



EQUATORIAL I 



AREA I 



Figure I 9 • "-Predomi nant movement of 

 albacore in the North Pacific 

 Ocean. Dashed lines passing 



through any blocl< indicate rela- 

 tively low vulnerability in that 

 block, and solid lines through a 

 block indicate high vulnerability. 

 The position of the arrows should 

 not necessarily be taken as the 

 geographic location of the migra- 

 tion route. 



might imply that most of the albacore in "mid- 

 ocean" (a region that was essentially unfished 

 for albacore) are taken in the longline fishery. 



Thus, several lines of evidence suggest that 

 after the albacore escape the North American 

 fisheries, they first become vulnerable, in large 

 quantities, to the Japanese pole-and-line fish- 

 ery. The escapement from the pole-and-line 

 fishery then provides a major source of fish 

 for the Japanese North Pacific longline fishery. 

 If we superimpose the movement pattern in- 

 duced from our study of moments upon the 

 larger pattern of predominant movement from 

 North American to Japanese pole-and-line to 

 Japanese longline fishery, we arrive at a more 

 detailed model of albacore migration in the 

 North Pacific than has heretofore been pro- 

 posed. The movement pattern induced from 

 moments is that the albacore move over the 

 longline and pole-and-line grounds in a north- 

 east to a southwest direction during the long- 

 line season and from a southwest to a northeast 

 direction during the pole-and-line season. This 

 feature of albacore apparent movement is well 

 known (see Van Campen, 1960 and Suda, 1963b); 

 the consistency of this movement in time and 

 space, has, however, not been previously de- 

 scribed. The results of applying the northeast 

 to southwest movement during the longline sea- 

 son and the southwest to northeast movement 

 during the pole-and-line season to the larger 

 Pacificwide movement pattern suggest that 

 after the albacore leave the North American 

 fishery, they migrate through or near the Jap- 

 anese longline grounds. (If the fish actually 



migrate through the longline grounds then their 

 vulnerability to the longline gear is extremely 

 low.) After passing the longline area the alba- 

 core enter the Japanese pole-and-line fishery 

 about April. After being exposed to the pole- 

 and-line fishery, the albacore migrate again 

 through or, in some sense, proximal to the 

 longline fishery, and again exhibiting little 

 vulnerability to the longline gear. At this time 

 their migration is in a southwest to northeast 

 direction. After passing through or in prox- 

 imity to the longline grounds the albacore spend 

 about 10 months in a refugium (possibly the 

 midocean area indicated by Otsu and Uchida), 

 unavailable to capture, somewhere to the north- 

 east of the longline grounds.^ After a period of 

 about 10 months the albacore move in a south- 

 west direction through the longline fishery in 

 which they exhibit maximum vulnerability to 

 the longline gear. After escaping from the 

 longline fishery the albacore proceed to the 



Indeed Koto (1963) shows that the albacore 

 taken on the broadbill-swordf ish longline grounds 

 centered about lat. 10° N. of the albacore long- 

 line grounds as considered in this paper are, on 

 the average, smaller than those taken on the 

 longline grounds, which is consonant with the 

 refugium concept. We should be cautious, however, 

 because the difference in average length between 

 the albacore taken on the albacore longline 

 grounds and the albacore taken on the swordfish 

 grounds might owe to a difference in the selec- 

 tivity of swordfish gear which is fished noctur- 

 nally with a different hook suspension system and 

 bait than that used for the albacore longline. 



27 



