crustaceans in areas 1 and 2, but less important 

 than crustaceans in area 3. Animals other than 

 fish, crustaceans, and moUusks — heteropods, 

 pteropods, larval Tonnidae, and tunicates — 

 amounted to less than 0.8 percent of the total 

 volume of food in both species. Unidentifiable 

 material consisted of semidigested masses of 

 various food, some of which was recognizable as 

 moUusks other than cephalopods. The percent- 

 age volume of unrecognizable material was low 

 for both species in areas 2 and 3 but was ex- 

 tremely high — much higher than that for any 

 other category of food— in skipjack tunas from 

 area 1 (fig. 4). 



FISHES 



Forage fish consumed by skipjack and yellow- 

 fin tunas in all areas consisted primarily of 

 juvenile and larval forms of pelagic fish. 



In area 1 (appendix tables 1 and 2) the fish 

 consumed by the two species differed. The 

 forage of skipjack tuna was made up of scom- 

 brids (Scomber spp. and Scomber scombrus) 

 and unidentifiable fish, whereas that of yellow- 

 fin tuna included fish from at least 15 families. 

 In areas 2 and 3, the food of skipjack and 

 yellowfin tunas was similar (appendix tables 

 3-6). In area 2 (appendix tables 3 and 4), 29 

 fish families were recorded for skipjack tuna 

 and 23 for yellowfin tuna; 19 were common to 

 the two species. A wide variety of forage 

 fishes was found in tunas from area 2, but only 

 a few taxa ranked high in frequency of occur- 

 rence and volume for both species. Large 

 numbers of Paranthias furdfer, Dactilopterns 

 volitans, and Holocanthus spp. were present — 

 the stomach of one yellowfin tuna contained 710 

 specimens of P. furcifer. In area 3 (appendix 

 tables 5 and 6), 38 forage fish families were 

 recorded for yellowfin tuna and 21 for skipjack 

 tuna ; 20 fish families were common to both. 



Among the families of forage fishes, in fre- 

 quency of occurrence and by volume, Scom- 

 bridae constituted the most important food of 

 skipjack and yellowfin tunas in area 1, and also 

 of skipjack tuna in area 2 (appendix tables 

 1-6). Serranidae occurred most frequently in 

 the diet of yellowfin tuna in area 2, and also 

 ranked high as forage of skipjack tuna. Other 

 fish in area 2 that ranked high in frequency of 

 occurrence and by volume for both tunas were 



Scombridae, Carangidae, Dactylopteridae, and 

 Chaetodontidae. 



In area 3, Carangidae, Tetraodontidae, Gem- 

 pylidae, and Serranidae were the most num- 

 erous forage fishes of yellowfin tuna ; they also 

 ranked high in frequency of occurrence and by 

 volume in the diet of skipjack tuna. 



CRUSTACEANS 



Crustaceans in stomachs of skipjack and 

 yellowfin tuna consisted of a wide variety of 

 forms. Larval macrozooplanktonic forms, 

 which made up the bulk of crustaceans in all 

 areas, were different types of zoea, megalopae, 

 or their equivalent stages. Amphipods (hy- 

 periids), Heterocarpus ensifer, mysids, and 

 euphausiids also were present but of less con- 

 sequence. 



Individual taxa of crustaceans contributed 

 little to the total volume of forage organisms. 

 Collectively — because of their substantial num- 

 bers and high frequency of occun-ence — crusta- 

 ceans were important in the forage of skipjack 

 and yellowfin tunas in area 3, where counts of 

 crustaceans exceeded those of fish (fig. 4). In 

 frequency of occurrence but not in volume, 

 crustaceans exceeded fish in the diet of yellow- 

 fin tuna in area 3. Crustaceans in the diets of 

 tunas in area 3 consisted of 34 taxa for skip- 

 jack tuna and 39 taxa for yellowfin tuna; 25 

 taxa were common to both species (appendix 

 tables 5 and 6). The chief constituents (fre- 

 quency of occurrence and by volume) in the 

 crustacean diet of the two species of tuna in 

 area 3 were larval stomatopods, and megalopal 

 stages listed as Decapoda (Brachyura) and 

 hyperiid amphipods. Although many amphi- 

 pods were present in the samples, they con- 

 sisted of relatively few species. Phrosina semi- 

 lunata was numerically the most important 

 species by far in the diet of both species of 

 tuna. Heterocarpus ensifer was the prominent 

 shrimp in the diet of yellowfin tuna; hermit 

 crab larvae (Petrochirus pustulatus, Dardanus 

 spp., D. arrosor, and D. pectinatus) and various 

 phyllosoma stages of Scyllarus sp. and Panuli- 

 rus rissoni were important in the diet of both 

 species in area 3 (appendix tables 5 and 6). 

 In area 1, crustaceans found in the stomachs 

 of only yellowfin tunas (appendix table 2) con- 

 sisted of hyperiid amphipods and megalopal 



450 



U.S. FISH AND WILDLIFE SERVICE 



