several depths in front 5 (table 1), using an 

 alpha-nneter of 1-m. beam path length (Tyler, 

 I960). These measurements were made con- 

 temporaneously with chlorophyll a determina- 

 tions, and at the same depths, as part of a 

 special, independent study. 



Zooplankton and Micronekton Standing Crop 



For each oblique, 1-m. net tow (except for 

 two tows in shallow water), 450 m. of wire 

 were paid out at 50 m./min. and, after a pause 

 of 1 minute, were taken in at 20 m./min. The 

 ship's speed (1-2 knots) was adjusted to main- 

 tain a wire angle of about 45°. 



All horizontal, surface, meter-net tows (on 

 50 m. of wire) at front 5 were made at night at 

 a speed of 1-2 knots; differences betweenhauls 

 due to effects of diurnal nnigration therefore 

 were probably small. 



Micronekton hauls also were made at night, 

 when micronekton is generally most plentiful 

 near the surface. The net used (Blackburn and 

 associates, 1962) had a square 5- by 5-ft. 

 frame at the mouth and was paid out on 350 m. 



of wire at 25 m./min. and hauled in at 10 m./ 

 min. Ship speed was 5 knots. 



Miscellaneous 



We noted the apparent abundance of easily 

 observed fauna, such as marlin, turtles, and 

 birds. 



The weather and sea conditions were re- 

 corded periodically, though they did not change 

 much on either TO-60-1 or TO-61-1. 



RESULTS AND DISCUSSION 

 Kinds of Water Available to Form the Fronts 



Before discussing the fronts, it seems desir- 

 able to provide an oceanographic context. The 

 following paragraphs describe the kinds of 

 water present in the general area, and their 

 relationships. 



Figure 1 shows the tracks of cruises TO- 

 60-1 (May 1960) and 6004-B (April I960) and 

 the places where fronts were studied. Figure 2 



MEXICO 



24" 



MAZATLAN 



22' 

 N 



20" 



N. 



II4°W 



II2''W 



IIO°W. 



I08°W 



I06°W 



Figure 2.— Surface isotherm contours (interval 1° C.) from data of cruises TO-60-1 and 6004-B (CalCOFI). The approxi- 

 mate relation of the fronts to this distribution can be seen by comparing this figure with figure 1 (^-•-speculative 

 contour). 



8 



