DRAGOVICH and POTTHOFF: FOOD OF SKIPJACK AND YELLOWFIN TUNAS 



Teuthoidea (squid) were the most important by 

 volume and by frequency of occurrence in the 

 diet of both species. Most of the squid belong 

 to the family Ommastrephidae. Among iden- 

 tified omasterphids, Ornithoteuthis antillarum 

 was most frequently encountered. This species 

 was especially numerous in the food of skipjack 

 tuna during UN6802. Octopoda were less nu- 

 merous and occurred with less frequency than 

 Teuthoidea. The displacement volume of some 

 of the Octopoda (Argonauta argo and A. sp.) 

 was very large. Five specimens of A. argo con- 

 sumed by yellowfin tuna during UN6802 dis- 

 placed 165.5 ml — more than all other mollusks 

 combined for that cruise or all the fishes for 

 that cruise (Appendix Table 4). 



Among other mollusks, pteropods and hetero- 

 pods were found in the stomachs of skipjack 

 tuna during both cruises. They were absent 

 in the food of yellowfin tuna during UN6802 

 and occurred only in two stomachs during 

 UN6801. A heteropod, CavoUnia longirostris, 

 occurred in high numbers in the diet of skipjack 

 tuna during UN6801. In terms of volume, both 

 of these mollusks were of minor importance. 



JUVENILE TUNAS AS FOOD OF 

 SKIPJACK AND YELLOWFIN TUNAS 



Knowledge on the distribution and abundance 

 of juvenile tunas and tunalike fishes is very lim- 

 ited because existing collection methods for 

 juveniles are inadequate. This information is 

 very important, however, as an aid in identifying 

 spawning seasons and areas of tunas. One of 

 the major sources of juvenile tunas is from 

 stomachs of adult tunas. Juvenile tunas and 

 tunalike fishes were present in the diet of both 

 species of tunas sampled on both cruises. As 

 many as 20 juvenile tunas were found in a 

 single tuna stomach. The most frequently en- 

 countered and the most numerous juvenile tunas 

 were Auxis spp. and little tunny (Euthynnus 

 alletterahis) (Table 2). Specimens of Auxis 

 spp. were found in both species of tunas during 

 both cruises. Specimens of E. alletteratus were 

 present in the diet of both species of tunas, but 

 only during UN6801. All the remaining species 

 of juvenile tunas occurred infrequently in small 

 numbers. Katsuivonus pelamis and Thunnus 



Table 2. — Occurrence of juvenile scombrids in the stomachs of skipjack and yellowfin tunas during cruises UN6801 



and UN6802. 



1093 



