BLACKBURN and WILLIAMS: DISTRIBUTION AND ECOLOGY OF SKIPJACK TUNA 



LATITUDE 



5N 



en 

 cr 



LlI 



I- 



UJ 



I 



H 

 Q. 



Figure 17.— Dissolved oxygen content (ml/liter), Part I transect, cruise Jordan 60, 5-11 March 1971. 



Om 



50 m 



b°N 



IO°N I5°N 



100 m h- 



ISOtn - 



200 m - 



250 m 



300 m 



350 m 



10 10 



5"^ 



lO'N 



IS'N 



Figure 18. -Temperature (°C) section from lat. 3°N, long. 

 124°20'W, to lat. 16°30'N, long. 146°06'W, cruise Cromwell 51, 

 November 21-26, 1970. 



much as possible without violating the data. Fewer 

 data were available for the March-April cruise 

 than for the November-December one, for reasons 

 given elsewhere. 



According to Blackburn and Laurs (1972), the 

 most conspicuous and consistent feature of day 

 and night forage distributions in the study area is 

 a zonally oriented maximum between lat. 0° and 

 5°N, which is probably associated with the equa- 

 torial upwelling as explained by King (1958). 

 Figures 23 and 24 show this feature, and Figures 



25 and 26 show one which is probably the same 

 although it does not appear to be zonally oriented. 

 Stations at the eastern end of the maximum in 

 Figures 25 and 26 were occupied 13 days after the 

 last stations at the western end were occupied, and 

 the maximum could have moved north in the in- 

 terval. Other maxima and minima in Figures 23 to 



26 are smaller and less consistent in location 

 between cruises. 



The data from these micronekton net hauls, es- 

 pecially those for the March- April cruise which are 

 very sparse, may not give a complete picture of the 

 distribution of skipjack forage. On the March- 



397 



