FOOD OF YELLOWFIN TUNA 



107 



STA. 



o 



a5 5.0 75 100 125 150 



ZOOPLANKTON VOLUME , CC /M? 



YELLOWFIN CATCH PER HUNORED HOOKS 



Figure 10. — Relation of zooplankton abundance, yellowfin catch per hundred hooks, and average volume of food per 

 stomach as found on cruise 11 of the Hugh M. Smith along 150° W. longitude for the range of latitudes indicated. 



abundance of these fish near land i9 related to the 

 greater abundance of crustacean larvae in such 

 areas. Is the distribution of the fish dependent 

 upon the availability of these food elements? 

 These questions cannot be answered from the re- 

 sults of this study, but they will be the objectives 

 of future research. 



Richer (1946) states that with few exceptions 

 large fish more often have empty stomachs than 

 do smaller ones of the same species. Our obser- 

 vations (table 5) indicate that just the reverse 

 may be true for the yellowfin. Richer states also 



that the average stomach content per unit of 

 body weight is less among large fish, which is in 

 general agreement with the results of this investi- 

 gation (fig. 5). 



There is some evidence that the rate of feeding 

 in fishes is directly proportional to the availability 

 of food. Therefore, in view of the average fisher- 

 man's belief that more tuna "feed" is found near 

 the reefs than offshore in the open ocean, it was 

 surprising to find that for comparable size groups 

 the fish taken offshore contained on the average 

 the same quantity of food in their stomachs as the 



