AROUND ISLANDS 



SURFACE DEEP 



OCEANIC 



DEEP 



I FISH ■ SQUID S CRUSTACEA □ MISCELLANEOUS 



Figure 6. Food of Yellowfin Tuna. To find out what 

 the tuna eat we have identified the material in the stomachs of many 

 tuna caught on our fishing surveys. Apparently yellowfin tuna eat 

 almost anything they encounter that is active, large enough to be 

 noticed, and small enough to swallow. The variety of sea animals 

 in their diet is outstanding and many are of surprisingly small size. 

 Over 75% of the stonriachs contained organisms weighing less than 

 one-tenth of an ounce. Occasionally quite large animals are eaten 

 too, the largest being a l6-inch skipjack found in the stomach of a 

 53-inch yellowfin. This simplifies the problem of finding their feed- 

 ing grounds. They should be anywhere in warmer waters where 

 general biological productivity is high. There is no need to find con- 

 centrations of a particular kind of feed. 



Consistent with this are the different proportions of the 

 various kinds of food in tuna taken from island and oceanic areas. 

 Within 5 miles of islands the surface tuna eat almost equal parts of 

 small reef fish and crustaceans such as the free-swimming young 

 stages of crabs and mantis shrimp, which in their adult form live 

 onthe reef and on the bottom in shoal water. Somewhat farther off- 

 shore but still within 10 nniles the crustaceans diminish and the 

 squids become a much larger element in the food of deep- swimming 

 tuna caught with longlines, and in truly oceanic areas the diet is 

 made up of almost equal parts of small fish and squid with very few 

 crustaceans. 



