FISHERY BULLETIN: VOL. 70, NO. 3 



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HMS-18 

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CAVALIERI 

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24" 



25' 26° 27° 



TEMPERATURE 'C 



28° 



Figure 29. — Relations between yellowfin tuna catch and 

 surface temperature at several longitudes for the zone 

 lying between lat 1° and 5°N. 



relation is striking and highly significant, and 

 finally on long 170°W the positive relation is 

 again suggested. Thus, with the exception of 

 long 140°W, all of the fish catch data agree with 

 the hypothesis that time variations can be ex- 

 plained in terms of the maturity of the water 

 and that variations in the biota can be estimated 

 by water temperature in this region. 



The single exception (long 140°W) appears 

 atypical in other respects. Good catches of tuna 

 were obtained in relatively cool water, but the 

 fishing evidently coincided with a time of rapid 

 change; a few days after the good fishing the 

 water cooled further and the fishing became poor. 

 Thus, the good fishing occurred during a change 

 from environmental conditions associated with 

 good fishing to those associated with poor fishing. 

 During such transitions we might expect irregu- 

 larities in the relation between water maturity 

 and catch. 



The fish catches and temperatures at long 148° 

 to 155°W plotted against time from 1951 to 1954 



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TEMPERATURE 



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26 



1951 



isbe 



1953 



1954 



Figure 30. — Temperatures and fish catches between long 

 148° and 155 °W plotted against time, 1951-54. 



(Figure 30) reveal the basic relation shown in 

 Figure 29. Generally cooler water and poorer 

 fishing are indicated, however, in 1951-54. Su- 

 perimposed on this trend is a suggestion of rising 

 temperatures during the first half of each year 

 and falling temperatures during the second half. 

 These bear some resemblance to the average 

 trends given in Table 2, but, insofar as these 

 data are adequate, a long-term trend to cooler 

 water appears to have almost completely sup- 

 pressed the seasonal trend during 1952, thus 

 pointing up the difficulties attending "seasonal 

 analysis" in the equatorial area. 



Temperature profiles. — It is instructive to ex- 

 amine the shape of the several meridional sur- 

 face temperature profiles at long 148° to 155°W, 

 because the average temperature that was com- 

 pared with yellowfin tuna abundance tends to ob- 

 scure certain important features. The several 

 profiles in Figure 31 suggest that a variety of 

 situations exists. 



Two of the profiles (panel A) show relatively 

 cool water from the equator to at least lat 4°N. 

 This "flat" feature at low temperatures suggests 

 very active upwelling and a northward displace- 

 ment of immature water; therefore, it is not 

 surprising that these two transects are associ- 



900 



