92 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Tinker (1944), Chapman (1946), and Hildebrand 

 (1946) briefly referred to the food of the yellowfin 

 tuna as consisting of small shore and pelagic 

 fishes, squid, and planktonic crustaceans. Herald 

 (1949) found a 42-mdlimeter seahorse, juvenile 

 surgeonfish, triggerfish, and other common forms 

 in the stomach of a yellowfin taken near the 

 Hawaiian Islands. Fitch (1950) found large 

 numbers of postlarvae of the pointed-tailed ocean 

 sunfish (Masturus lanceolatus) in yellowfin from 

 Hawaiian waters. 



All of these investigators listed the kinds and, 

 in a few cases, the numbers of organisms that were 

 found in the stomachs of yellowfin tuna, but they 

 gave no quantitative analysis of the relative 

 importance of the various food elements or their 

 relation to locality, habitat, or body size of the 

 tuna concerned. Welsh (1949), on the other hand, 

 has made a quantitative study of the food of the 

 yellowfin, but only 20 relatively small specimens, 

 all captured within }{ mile or less of Oahu, Ha- 

 waiian Islands, were examined. Ronquillo (1950) 

 examined the stomachs of 144 yellowfin from the 

 waters of the southern Philippines and made a 

 preliminary report and checklist of organisms 

 found and their frequency of occurrence. 



The authors are grateful to fellow staff members, 

 ships' officers and crews of the Hugh M. Smith, 

 John R. Manning, and the Henry O'Malley, for 

 their assistance in handling these large fish at sea 



and in removing and preserving the stomach 

 material. 



SOURCE OF MATERIALS 



Material collected in 1950 and 1951, during 12 

 cruises of Fish and Wildlife Service vessels 2 in 

 waters surrounding the Line and Phoenix Islands, 

 was available for this investigation (table 1). Of 

 the 5,164 yellowfin captured on these cruises, the 

 stomachs from 1,097 were preserved for sub- 

 sequent analysis. Of the 1,097 fish sampled, 786 

 were taken at the surface by trolling or by live- 

 bait pole-and-line fishing, and 311 were caught at 

 depths of 100 to 500 feet with longline gear. 3 

 A total of 775 of the surface-caught fish and 70 of 

 those taken on longlines were captured within 10 

 miles of land (table 2). The remaining 1 1 surface- 

 caught fish and 241 subsurface-caught fish were 

 taken in waters 10 miles or more from land. 



The sampled yellowfin ranged widely in size, 

 from approximately 500 to 1,700 millimeters (5 to 

 200 pounds) . The length distribution of these fish 

 is given in figure 1. For purposes of comparison 

 the fish were classified in three size categories: (1) 

 small, less than 1,000 mm. fork length, or approx- 

 imately 43 lb.; (2) medium, 1,000 to 1,299 mm. 



1 The Hugh M. Smith, John R. Manning, and Henry O'Malley. 



1 The live-bait method of tuna fishing has been described by Godsil (1938), 

 the longline method by Shapiro (1950) and June (1950), and surface trolling 

 by Bates (1950). 



Table 1. — -Distribution of the yellowfin tuna taken and stomachs collected in the central Pacific, by lime of year, cruise, 



locality, and fishing method, 1950 and 1951 



