Figure 13, in effect, summarizes the data from Hugh M, 

 Smith cruise 11 and lends support to the above quotation c In this 

 figure, surface values for temperature, salinity, oxygen, and phos- 

 phate, the current speed, the zooplankton volumes, and the yellowfin 

 catch have been plotted against latitude (vertical scale ). The first 

 five fields plotted, namely, T„ S, O2, P0 4 , and current speed repre- 

 sent conditions as observed during the period of the cruise c The zoo- 

 plankton, although sampled during the cruise, may be considered as 

 the culmination of a series of events which had their origin during 

 some previous period of upwelling, probably some distance to the 

 east. The charge of nutrients thus brought to the surface was uti- 

 lized by phytoplankton, and indirectly for the succeeding trophic 

 levels, zooplankton, forage fish and squid, and the tuna„ 



Although we do not know the time required for the con- 

 version of nutrients through the trophic levels to the tuna, the data 

 presented in figure 13 suggest the integrated relationships among the 

 oceanographic and the biological factors. The curves for the various 

 fields (figa 13) nicely define the zones of interest„ Reading from north 

 to south (top to bottom) the North Equatorial Current extends south to 

 about 10° No, the Equatorial Countercurrent between 10 N„ and 5 N„ , 

 and the South Equatorial Current from 5° N. to the southern limit of 

 the section. The equatorial divergence is centered at 1 S. with the 

 zone of convergence between this latitude and the southern boundary 

 of the Countercurrent. Within the Countercurrent the salinity curve 

 shows the typical increase toward the southern edge. The values for 

 surface phosphates, associated with the center of upwelling, are 

 somewhat atypical, with higher than usual values from the southern 

 boundary of the section and lower values between the upwelling and 

 the southern boundary of the Countercurrent. Several reasons for 

 this could be advanced including mixing with surface waters of lower 

 PO4 during the meridional transport (1° to 5 N„), variations in in- 

 tensity of upwelling from cruise to cruise, and a reflection of the 

 biological activity in the waters moving in from the east. 



The latitudinal variations in the abundance of zooplankton 

 (fig. 13F) lend emphasis to the proposition of enrichment from the 

 equatorial divergence. A more detailed discussion of this relation- 

 ship between the plankton and the fish in this area is to be found in 

 the report by Murphy and Shomura (1953) and in the report by Sette 

 (MS) 



11 



