the most common identifiable group of the food 

 fishes utilized by the yellowfin in our samples. 



Dolphin 



An examination of the stomachs of 52 

 dolphin ranging in size from 41.3 to 121. cm. 

 showed the importance of fish in their diet 

 (table 14). Cephalopods and crustaceans togeth- 

 er comprised less than 3 percent of the total 

 volume. Flyingfishes ( Exocoetidae ) appeared 

 to be particularly significant both in volume and 

 occurrence. Welsh's study of 58 stomach sam- 

 ples showed almost identical results. Flying- 

 fish have also been reported in the food of 

 dolphin caught in North Carolina waters (Schuck 

 1951). 



Cymothoid isopods were found in two stom- 

 achs. Members of this family are known to be 

 parasitic on fish. It is possible that they were 

 parasitic on the food fishes and thus incidentally 

 ingested. One of the stomachs containing cymo- 

 thoid isopods also contained a monacanthid, an 

 exocoetid, and unidentified fish remains. The 

 other contained exocoetids and a syngnathid in 

 addition to the isopod. 



A further item of interest was the presence 

 of a coral rock about 1/2 cm. •* in volume in one 

 of the stomachs. The rock may have been in- 

 gested accidentally while feeding on reef-dwelling 

 forms. Other contents of this stomach were 

 penaeid shrimps, stomatopod larvae, a crab 

 megalopa, remains of a fish, and remains of a 

 squid. 



Wahoo 



All three of the stomachs examined 

 contained remains of fish. One of the food 



fishes was identified as a carangid. The sizes 

 of these three wahoo were 104.1, 111.1, and 

 ca. 123 cm. 



Frigate Mackerel 



Of the two frigate mackerel stomachs 

 examined, one contained numerous crab mega- 

 lops and stomatopod larvae, while the other 

 contained 8 crab megalops, numerous stomato- 

 pod larvae, 2 anomuran larvae, and a small 

 octopus. The frigate mackerel were 33.2 and 

 36. 6 cm. in length. 



General Discussion 



The relative importance by volume of the 

 three major food categories for the skipjack, 

 little tunny, yellowfin, and dolphin is portrayed 

 in figure 10. The little tunny and dolphin appear 

 to rely heavily upon fishes for food, while the 

 skipjack and yellowfin have a more varied diet 

 utilizing all three of the major food groups. 



The similarity between the diets of skipjack 

 and yellowfin and between little tunny and dolphin 

 suggests the likelihood of interspecific 

 competition. Evidence of competition for food 

 between skipjack and yellowfin was furnished on 

 several occasions when the Salpa would catch 

 both species while trolling under a working bird 

 flock. The occurrence of the same invertebrate 

 organisms in the stomachs of both skipjack and 

 yellowfin seems to attest the presence of com- 

 petition, but the absence of food fish species 

 common to both fails to support it (tables 11 and 

 13). Evidence for competition between the little 

 tunny and the dolphin may be seen in the number 

 of food fish species common to both (tables 12 

 and 14). The fishes most prevalent in the food 

 of the dolphin, however, were the flyingfishes 



| FISH ] CEPHALOPODS ^] CRUSTACEANS 



SKIPJACK 



LITTLE TUNNY 



YELLOWFIN 



DOLPHIN 



Figure 10. --Relative importance of fishes, cephalopods, and crustaceans in the 

 diets of skipjack, little tunny, yellowfin, and dolphin. 



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