SECKEL: SKIPJACK AND ENVIRONMENT 



WEST LONGITUDE 



Figure 13. Locations of drifting objects in June of the third model year that were introduced in each of the pre- 

 vious 30 months at long 120°W. Dashed lines indicate most westerly location reached by objects introduced every 

 quarter. 



WEST LONGITUDE WEST LONGITUDE 



geostrophic current (Figure 9) becomes impor- 

 tant. The effect of convergence of this compo- 

 nent of flow with the northward wind-driven 

 current is evident at the northern edge of the 

 distribution of drifting objects in Figure 13. 



As the objects drift westward north of lat 

 18°N and west of long 140°N, they enter the 

 region of decreasing speed in the North Equa- 

 torial Current (Figure 9) and therefore tend to 

 accumulate further (Figure 13). 



THE MODEL OCEAN AND SKIPJACK 



The minimum duration of drift of objects from 

 long 120°W to the quadrant north of lat 19°N 

 and west of long 155°W ranges from 21 to 23 

 months (Table 7) . These times are of the same 

 order of magnitude as the times skipjack tagged 

 in the eastern Pacific were free except for the 

 two skipjack tagged near Clipperton Island 

 (Table 5) . If the model ocean is realistic, these 

 results indicate that the mean velocity of the fish 

 relative to the water (Vf) is small compared to 

 the mean velocity of the water ( Vw) . The paths 

 of the fish, of course, are not known and many 

 routes and modes of travel behavior can be post- 

 ulated. However, there is one, the simplest mode 



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Figure 14. — Left Panel: Position of objects in March 

 that were introduced at long 120 °W during the previous 

 October, November, and December. Right panel: Posi- 

 tions of objects in September that were introduced at 

 long 120 °W during the previous April, May, and June. 



Table 7. — Minimum duration of drift from long 120°W 

 to the quadrant north of lat 19 °N and west of long 

 155°W. 



779 



