stages of Brachyura; one group of megalopae, 

 Raninidae, was identified to family. In area 2, 

 megalopal forms — Decapoda (Brachyura) and 

 larval stomatopods — ranked high in frequency 

 of occurrence. Mysis stages of Cerataspis petiti 

 were present in the diet of yellowfin tunas in 

 area 2 only (C. petiti has never before been 

 reported from the Caribbean Sea). 



MOLLUSKS 



Numbers of identified moUusks were consid- 

 erably fewer than those of fishes and crusta- 

 ceans. Squids (Ommastrephidae) were most 

 numerous in the diet of both species of tunas 

 in all areas (appendix tables 1-6). lUex ille- 

 cebrosus and Ommastrephes spp. were the only 

 identified ommastrephids. Pelagic juvenile oc- 

 topuses were present in the stomachs of both 

 species of tunas. The identified octopods, 

 Tremoctopus violaceus, were observed in area 

 2 (appendix tables 3 and 4). 



OTHER FOOD 



Heteropods and pteropods were prominent 

 in frequency of occurrence for both species of 

 tuna, but were unimportant volumetrically. 

 The two groups of mollusks were present in 

 the stomachs of skipjack tuna in areas 2 and 3 

 (appendix tables 3 and 5) and in yellowfin tuna 

 in area 3 (appendix table 6). By frequency of 

 occurrence and volume, heteropods and ))tero- 

 pods were more important in the diet of skip- 

 jack tuna than in that of yellowfin tuna in all 

 areas. Oxygyrus keraudreni, Cavolinia uni- 

 cinata, and Diacria trispinosa were identified 

 from area 2 ; 0. keraudreni was the heteropod 

 found most frequently in both species of tunas 

 in area 3. 



Larval Tonnidae (including Tona galea) 

 were present in the stomachs of skipjack tuna 

 in area 2 only. 



JUVENILE TUNAS AS FOOD FOR 

 SKIPJACK AND YELLOWFIN TUNAS 



Information on the distribution and occur- 

 rence of juvenile tunas is of great value in 

 identifying the spawning areas of tunas, but 

 the collection of juvenile tunas by standard 

 means is difficult. Tunas themselves, however, 

 are excellent collectors of many marine species, 

 including other tunas. Juvenile tunas were 



present in all three areas (table 2). All tunas 

 found in the stomachs of skipjack and yellowfin 

 tunas in this study were juveniles; most were 

 identified from vertebrae. 



As many as 13 juvenile tunas were found in 

 the stomach of a skipjack tuna, and as many 

 as 24 in the stomach of a yellowfin tuna. Auxis 

 spp. (436 specimens, 23-134 mm. long) were 

 the most numerous scombrid in the stomachs 

 of both tuna species (unidentified Scombridae 

 were the only other form recorded for both) ; 

 Euthynnus alletteratus (40-42 mm. long), 

 Katsuiuonus pelamis (46-94 mm. long), Thun- 

 nus spp. (64-72 mm. long), and T. athinticus 

 (59 mm. long) were present in the stomachs of 

 skipjack tuna only (one to three specimens per 

 stomach) ; juvenile Scomber japonicus (83- 

 222 mm. long) were present in the stomachs 

 of yellowfin tunas only (one to four per stom- 

 ach). 



Table 2. — Occurrence of juvenile scombrids in the 

 stomachs of skipjack and yellowfin tunas in areas 

 1, 2, and 3 



[For the areas see fisure 1] 



Area 1 Area 2 Area 3 



Skip- Yellow- Skip- Yellow- Skip- Yellow- 

 jack fin jack fin jack fin 



Scomber spp. -\- -\- 



Scomher japonicus + 



Sco-mber acombrus -t- 



Other Scombridae + + + + + 



Scombroidei -t- 



Auxia spp. -f- -I- -f -|- 



KatBuwonuB petamit -|- 



Kuthymiua 



alletteratuB -^- -^- 



Thtmnita spp. -f- 



Thunnua attanticua -j- 



That juvenile tunas are a part of the diet 

 of adult tunas has been reported often. King 

 and Ikehara (1956) found juvenile skipjack 

 tuna in the stomachs of yellowfin and bigeye 

 tunas; Nakamura (1965) reported a high fre- 

 quency of occurrence (24.8-44.8 percent) of 

 juvenile tunas in the stomachs of skipjack 

 tunas; Suarez-Caabro and Duarte-Bello (1961) 

 observed juvenile blackfin tunas (5-150 mm., 

 fork length) and skipjack tunas (35-145 mm., 

 fork length) in the stomachs of skipjack tunas; 

 Reintjes and King (1953) found skipjack tuna 

 and various other tuna species in the stomachs 

 of yellowfin tuna; and Koga (1958a, b) and 

 Alverson (1963) reported juvenile tuna in the 

 stomachs of other tunas. 



SKIPJACK AND YELLOWFIN TUNA FOOD IN ATLANTIC OCEAN 



451 



