Yellow-fin Tuna 



The yellovi-fin catches of these four cruises indicate a center of abundance in the 

 region of 140 -150 W, longitude, just north of the Equator. East and west of this zone the 

 abundance fell off markedly, particularly to the east. This agrees in general with earlier find- 

 ings. 



The section at 120 W. longitude (fig. 2, table 1) gives e\-idence of very intens- up- 

 welling of the t>-pe described by Cromwell (1953). This is indicated by the cooler surface water 

 at the Equator. The general distribution of this cool water indicates that it is being moved north- 

 ward, as would be expected under the prevailing winds. The yellowfin appear to have been vir- 

 tually absent from this newly upwelled water, although they were taken to the north and south of 

 it (fig. 2). This is understandable if it is hypothesized that the newly upwelled water had not 

 been in the euphotic zone long enough to develop a population of tuna forage. 



The section on 130 W. longitude (fig. 3, table 1) rather closely resembles the 

 120 W, section in respect to the distribution of isotherms and the distribution of yellowfin, ex- 

 cept that on the former the surface temperatures were somewhat higher and the yellowfin more 

 abundant in the region of upwelled water. The slightly higher surface temperatures along 130 W. 

 might indicate that the upwelling had been less intense or from shallower depths, or it might 

 mean that the water had been in the photos ynthetic zone for a longer period of time. If the latter 

 were true, tuna feed might have accumulated, leading to the somewhat denser population of 

 yellowfin evidenced by our catch rates. 



Table 1. --Summary of the tuna catch. Smith cruise 18 (more 

 complete data will be found in the appendix) 



