374 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



140° 



140° 150° 160° 170° 180° 170° 160° 150° 140° 130° 120° 110° 100° 90° 80° 



Figure 6. — Resultant direction and force of surface winds in the central equatorial Pacific during March (A), a month 

 of light and variable winds on the Equator but strong northeast trades in the region of the Countercurrent, and 

 during August (B), a month of strong southeast trades on the Equator and light winds along the Counter-current. 

 [From Atlas of Climatic Charts of the Oceans, U. S. Weather Bureau, 1938. Arrows show resultant wind direction 

 computed for each 5-degree unit area. Shadings indicate gradations of resultant velocities scaled in Beaufort units of 

 wind force.] 



east of 160° W. tlian to the west of that longitude 

 and also more to the north of the Equator than to 

 the south. A narrow convergent zone which 

 theoretically should concentrate the zooplankton 

 is most likely to occur east of 160° W., and par- 

 ticularly east of 140° W., because of the promi- 

 nence of the southeast trades in that region. 



ZOOPLANKTON AND THE CURRENT 

 SYSTEM 



Within the range of latitude sampled, there are 

 certain natural subdivisions of the environment 

 which may be established on the basis of the 

 current structure. These may be defined as 

 follows: (1) the North Equatorial Current from 



