FISHERY BULLETIN: VOL. 73, NO. 2 



(Figures 5, 6, 7, 8). The only apparent relationship 

 between surface temperature and skipjack abun- 

 dance appears to be the high abundance in the 

 western part of the area of strong temperature 

 gradient at lat. 1° to 3°N in November-December 

 1970. 



Mixed Layer Depth 



The depths (meters) of the bottom of the mixed 

 layer are contoured at 20-m intervals in Figures 14 

 and 15 for Part II of the cruises. Figures 10 and 11 

 show the depths on Part I. Even though data are 

 zonally discontinuous in parts of Figures 14 and 



125° W 



120** 



II5*W 



19^ 



9*H 



0». 



9^ 



.en 



":u 



20 ~Q' 





.KTU 



'2°-Cs^. 



>60 



• JOROaN 



• CROHWILL 



60 

 40 



<46/ ' ' ^^^-^^0 



izvw 



.9*»( 



9*S 



HTW 



Figure 14.-Depth (m) of upper mixed layer, Part II operations, 

 cruises Jordan bl-Cromwell 51, November-December 1970. 



15, they are generally consistent with those of 

 Cromwell (1958), Wyrtki (1964), and Love (1971b, 

 1972a, b, in prep.: EASTROPAC data). 



In November-December 1970, the mixed layer 

 depth was shallow ( < 40 m) north of lat. 9°N, but 

 south of there increased rapidly to > 100 m in the 

 region of lat. 5°N. This ridge and trough are to be 

 expected at the approximate northern and 

 southern boundaries of the surface NECC. The 

 gradient of change from this trough southwards to 

 another ridge was particularly intense in the east- 

 ern edge of the area around lat. 4°N. In March- 

 April 1971, the mixed layer was very shallow over 

 most of the area surveyed south of lat. 10°N, 

 becoming < 10 m in the region lat. 3° to 4°N. The 

 even depth of the mixed layer from lat. 4° to 10°N 



IS'N 



lO'N 



5'N 



5'S 





40 

 40 



40 



>40 



I5*N 



5*N 



-0« 



5'S 



I20'W 



II5*W 



Figure 15.-Depth (m) of upper mixed layer, Part II operations, 

 cruise Jordan 60, March-April 1971. 



394 



