46 Charles S. Manooch, III and Diane L. Mason 



blackfin tuna. Percent volumes of these mollusks were less than 2% for 

 both predators, and whereas over 430 squid were consumed by the 

 tunas, less than 30 paper nautilus were eaten. At least three genera of 

 squids were ingested: Loligo, Sepioteuthis, and Illex. Generic identifica- 

 tions were obtained by comparing saved, pooled samples with reference 

 collection specimens and therefore do not appear in the tables. 



Crustaceans. — Crustaceans, important foods of both species and 

 second only to fish in overall frequency of occurrence, were identified in 

 52% of the yellowfin and in 67.4% of the blackfin. The majority were 

 immature stages (larvae, megalopa and glaucothoe). Due to the small 

 sizes of the animals, the relative percentages of the total food volume — 

 5.9% for yellowfin and 8.4% for blackfin — were comparatively small. 

 Major taxa in the diet of yellowfin by frequency of occurrence were 

 Raninidae (27.5%), Penaeidae (12.2%), Stomatopoda (7.7%), Portuni- 

 dae (7.1%), and Dromiidae (6.1%). For blackfin tuna, the most fre- 

 quently encountered were Stomatopoda (34.8%), Diogeninae (16.9%), 

 Raninidae (15.7%), Penaeidae (14.6%), and Dromiidae (12.4%). In all, 

 over 5,000 individuals were enumerated, and on one occasion a single 

 predator contained hundreds of these small, mesopelagic invertebrates. 



Our findings of the overall food habits seem to agree closely with 

 those of Dragovich (1970), who described fish, cephalopods and crusta- 

 ceans as the major foods of yellowfin and skipjack, Katsuwonus pela- 

 mis, tunas in the Atlantic. He also mentioned that larval and juvenile 

 stages were prevalent for ingested fishes and macrozooplanktonic crus- 

 taceans. 



Miscellaneous. — The very nature of tuna feeding, near-surface strain- 

 ing as well as actively pursuing and capturing larger animals, results in a 

 variety of items being consumed that are probably ingested by accident 

 along with natural foods. Yellowfin tuna had the most diverse assemb- 

 lage of non-food items (31.6% frequency): plants {Sargassum, Zostera, 

 Thalassia and Spartina), feathers, globs of tar, and plastic. Miscellane- 

 ous items occurred in only 15.7% of the blackfin, represented by Sargas- 

 sum, Zostera and plastic. Sargassum was found in 26.5% of the stom- 

 achs with food, and usually occurred in tunas captured off North 

 Carolina. This percentage is similar to the 37.8% reported for Sargas- 

 sum removed from the digestive tracts of skipjack tuna captured earlier 

 from approximately the same geographical area (Batts 1972). 



Other studies also revealed a dominance of fish, squid and crusta- 

 ceans in tuna diets for the Atlantic and Pacific. Reintjes and King 

 (1953) investigated the food habits of 1,097 yellowfin from the Central 

 Pacific and found that fish occurred in 70.4% of the stomachs; squid in 

 55.4%; and crustaceans (mostly immature, pelagic stages) in 66.9%. 

 Alverson (1963) found fish, squid and crustaceans occurring in 53.8%, 



