74 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Table 6. — Varialion in volume and composition of stomach contents with longitude of place of capture 



the SEC from 1/2° S. to the southern hmit of our 

 samphng (14° S.). 



These areas have the following characteristics 

 affecting the abundance of fish food: Area 1 is a 

 region of low zooplankton concentrations (King 

 and Demond 1953) and sliallow thermocline. In 

 area 2 the thermocline deepens to the south, and 

 zooplankton shows some increase in abundance. 

 Area 3 has a deep thermocline and a relatively 

 high concentration of zooplankton. In area 4 at 

 the Equator, upwelling is evidenced by a doming 

 of the isotherms, a reduction in surface tem- 

 perature, an increase in surface inoi-ganic phosphate, 

 and frequently by the greatest concentration of 

 zooplankton. In area 5 the thermocline deepens, 

 and the zooplankton concentration is reduced. 



When the yellowfin and bigeye catch i-ecords ^ 



' Summarized in reports of Murphy and Shomura (1953a, 1953b, 1955). 



during the years 1950-53 are combined according 

 to these natural features of the environment, we 

 observe (fig. 11, A) that the area of best catch for 

 yellowfin was in the convergence zone (area 3), 

 while the best catches of bigeye came from the 

 NEC (area 1) and the CC (area 2). Thus the 

 longline catch provides some indication of an 

 inverse relation in the abundance of these two 

 species. 



The stoniacli-coiitent volumes were combined 

 in the same manner — disregarding the rather 

 minor differences associated with depth of capture, 

 longitude, and season — to produce parts B and C 

 of figure 11.* For tlie yellowfin, we find no cor- 

 respondence between catch per 100 hooks and 



' Parts B and C of figure 11 are based on the 439 yellowfin stomachs em- 

 ployed in this report, which were considered comparable with the bigeye 

 collections, and not on our total yellowfin-stomach data from the central 

 Pacific. 



