Comparative Food Studies of Yellowfin Tuna, Thunnus 



albacares, and Blackfin Tuna, Thunnus atlanticus 



(Pisces: Scombridae) from the Southeastern 



and Gulf Coasts of the United States 



Charles S. Manooch, III 



AND 



Diane L. Mason 



National Marine Fisheries Service, 



Southeast Fisheries Center, Beaufort Laboratory, 



Beaufort, North Carolina 28516-9722 



ABSTRACT. — Two hundred and six yellowfin tuna, Thunnus alba- 

 cares, and 98 blackfin tuna, T atlanticus, were sampled from sport 

 fisheries in the South Atlantic and Gulf of Mexico, April 1980 to July 

 1982. Stomach contents were analyzed by frequency of occurrence, 

 number of food items, and volume. Invertebrates (85%) and fish (77%) 

 occurred in the diet of yellowfin relatively equally. Major invertebrates 

 by frequency of occurrence were cephalopods (62%) and crustaceans 

 (52%). Fishes were represented primarily by the families Scombridae 

 (12.2%), Balistidae (11.2%), and Syngnathidae (8.2%). Yellowfin also 

 ingested floating materials such as plastic, feathers, seagrasses, and 

 balls of tar. Invertebrates occurred in 82% of the blackfin stomachs 

 with food, and represented 75% and 31% of the foods by number and 

 volume, respectively. Fish were found in 67% of the stomachs and con- 

 stituted 26% and 68% of the food number and volume, respectively. 

 The most frequently occurring invertebrates were crustaceans (67.4%) 

 and cephalopods (36.0%). Fishes were represented primarily by the 

 families Balistidae (10.1%), Trichiuridae (5.6%), and Carangidae (4.5%). 

 Blackfin also consumed floating materials, such as plastic and sea- 

 grasses. Statistical comparisons of the diets of the two species indicated 

 no significant correlation. Overall, their diets appear to reflect those of 

 fast, aggressive predators, and also of fish that use their gill apparatus 

 to strain small, near-surface items from the water. 



INTRODUCTION 



The family Scombridae includes many species of pelagic fish that 

 are very important to the world's fisheries. Some, such as the mackerels 

 Scomberomorus spp. and Scomber spp., are primarily coastal, migrat- 

 ing north in spring and summer and south in fall and winter. Others, 

 including members of the genus Thunnus, are usually much larger than 

 the mackerels and are reputed for their more complex, often transoce- 

 anic migrations. 



Two species of Thunnus, the yellowfin tuna, T. albacares, and the 

 blackfin tuna, T. atlanticus, are highly esteemed food and sport fishes 

 whose distributions include the southeastern and Gulf coasts of the Uni- 



Brimleyana No.9:33-52. June 1983. 33 



