FOOD OF BIGEYE AND YELLOWFIN TUNA 



69 



SQUID 



FISH 



100 



90 

 80 - 

 w 70- 



UJ 



2 



I- 50 



z 



UJ 



" 40 



o 

 30 



ID 



3 

 O 



20 

 10 



O 

 100 



YELLOWF 



(109) 



(120) 



(165) 



i- A 



90 - 

 80  

 70 



60 



UJ 



Z 

 I- 50 



z 



UJ 



<-> 40 



u 



5 30 

 o 

 20 



10 







BIGEYE 



(18) 



(45) 



SHALLOW 



INTERMEDIATE 



DEEP 



FinuRE 8. — Variation in the major food categories (total 

 fish and squid) as related to the depth at which the tuna 

 were captured. Number of stomachs is shown in 

 parentheses. 



yellowfin (tahlp 4), and in the bigeye the average 

 food vohune increased with greater distance from 

 land while in the yellowfin the volume varied 

 irregularly. 



Variation with Season and Longitude 



To examine differences related to time of sampl- 

 ing, the various cruises were grouped into four 

 seasonal periods, as indicated in table 5. For 

 botii species the largest average volume of food 

 occurred in the April-July period, with ()ctob(>i- 

 Xovember averaging the lowest in the yellowfin 

 and August-September the lowest in the bigeye. 

 If we consider the average volinnc per stomach of 

 the major food elements, we find tlial, in our 

 samples of both tunas, fish were consumed in 



greatest amount during April-.Tuly and in least 

 amount during August-September (fig. 9 and 

 table 5). The average volumes of squid and the 

 major fisli families represented in the food did not 

 vary in parallel fashion for thebigeyeandyellowfin. 

 When the data from the various cruises are 

 combined with regard to longitude but witliout 

 regard to time of year, we obtain the results pre- 

 sented in table 6, with the variation in availability 



^ SQUID 



TOTAL FISH 



I80'>-I55"' 



1 50<^ 140° 

 WEST LONGITUDE 



1 30°- 1 20° 



/<-■ 



FiciRE * — Variation in the major foods as related to 

 time of year that the tuna were captured. Number of 

 stomachs is shown in pareiithe.ses. 



