investigate the abundance of yellowfin tuna with respect to certain 

 physical, chemical, and biological features of equatorial waters 

 away from the influence of emergent land masses, " 



The results of the longline fishing have been described by 

 Murphy and Shomura (1953); the detailed plankton studies will be re- 

 ported later 



The station pattern for the oceanographic phase of cruise 11 

 was planned to duplicate the positions of the fishing stations occupied 

 along the southbound leg„ The positions of the fishing and oceanographic 

 stations are shown on figure 1 (all figures are grouped at the end of 

 the text) The data for the 22 stations appear in tabular form at the 

 end of this report a These data, along with those from the bathythermo- 

 graph lowerings, are represented by vertical sections, figures 2, 3, 

 and, 7 to 12. 



In the vertical sections, the position of each sample is 

 indicated by a dot If for some reason (thermometer stuck, Nansen 

 bottle leaked, bottle pretripped, etc„) it can be definitely ascertained 

 that the value for the particular field is in error, it is discarded, the 

 dot is not carried, and the deleted value is indicated by a dash in the 

 tabulated data If a particular value is in doubt, but there is no ap- 

 parent reason for its being in error, the dot is shown, the value is 

 carried in the tabulated data and an appropriate footnote appended. 



Temperature ; The temperature sections, figures 2 and 

 3, have been constructed from bathythermograph observations „ The 

 data for figure 2 were collected during the southbound leg of the cruise 

 (fishing) and those for figure 3 during the northbound leg (oceanogra- 

 phy). The isotherms are plotted at 2-degree (F„) intervals; the maxi- 

 mum depth of penetration is indicated by a dash„ 



During the southbound leg of the cruise, five BT's were 

 taken at the positions of each fishing station, and one at each 10-mile 

 interval between stations,, The data are plotted at 30-mile intervals 

 in figure 2„ During the return section lowerings were made at 10- 

 mile intervals between 5 S. and 12 N. and at 30=mile intervals 

 from 12 No to 19 N c All lowerings are plotted in figure 3. 



The most striking features of the two vertical tempera- 

 ture sections, reading north to south in figures 2 and 3, are (1) the 

 shallow, well developed thermocline in the region of the northern 

 boundary of the Countercurrentj, and (2) the cooling of the surface 

 water in the region of the equatorial divergence „ Typical temperature- 

 depth traces, reconstructed from BT's taken in these regions, are 

 shown on figure 4. 



4 



