NORTH PACIFIC 

 _0 C E A N 



1 MARSHALL IS, 



AMERICAN SAMOA 



°FIJI IS 



?NEW ZEALAND 



E 120° 130° 140° 150° 160° 170° 180° 170° W. 



Figure 10. — Range and migration routes of slapjack tuna of the western subpopulation. The 

 eastern limit of distribution is indicated by thin solid line (northern winter) and broken line 

 (northern summer). Migration routes are shown by arrows. The numerals with A or B 

 represent age classes of fish from summer or winter spawning, respectively. Intensive 

 spawning grounds in the northern summer and northern winter are shown by horizontal and 

 vertical hatching, respectively. [Reproduced from Fujino (1972).] 



ed south of lat. 15°N rapidly drifted northward and all 

 were north of lat. 15°N by the time they had crossed 

 long. 128°W; that the objects appeared to concentrate 

 on the northern and southern edges of their distribution 

 and to merge west of long. 150°W in a relatively 

 narrow band between lat. 18° and 22°N, so that the 

 initially meridional distribution of objects along long. 

 120°W became oriented along the northern edge of the 

 equatorial current west of long. 160°W after 24 mo. The 

 minimum duration of drift of objects from long. 120° to 

 155°W ranged from 21 to 23 mo, which is of the same 

 order of magnitude as the duration of freedom of four of 

 the seven skipjack tuna tagged in the eastern Pacific 

 and recovered in Hawaii. As a result of this model 

 Seckel (1972) postulated that a possible, and the sim- 

 plest, mode by which skipjack tuna travel from the 

 eastern Pacific to Hawaii, is by swimming randomly and 

 drifting with the current. 



Williams' (1972) proposal included three migration 

 models of young skipjack tuna that enter the eastern 



Pacific fishery areas on the basis of oceanog^aphic condi- 

 tions and events in the central-east Pacific. In the first 

 model (active migration), he proposed that skipjack tuna 

 larvae and early juveniles in the equatorial area west of 

 long. 130°W are located principally in the westward 

 flowing North Equatorial Current (NEC) and South 

 Equatorial Current (SEC); that the juveniles orient 

 themselves eastward and migrate in that direction along 

 the zonal "productivity" bands at the northern and 

 southern boundaries of the North Equatorial Counter- 

 current (NECC) and enter the offshore areas of the 

 southern fishery; that the cessation of the surface NECC 

 east of long. 120°W from January through May disrupts 

 the orientation and movement of skipjack tuna juveniles 

 through significant changes in the position and continu- 

 ity of the "productivity" bands, at which time the 

 skipjack tuna are reoriented to the northeast and enter 

 the northern fishery following a "food bridge" (i.e., 

 pelagic stages of the red crab, Pleuroncodes pUmipes), 

 linking that area with the Revilla Gigedo Islands and 



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