Food of Western North Atlantic Tunas (Thunnus) 

 and Lancetfishes (Alepisaurus) 



FRANCES D. MATTHEWS,' DAVID M. DAMKAER,^ 

 LESLIE W. KNAPP, 3 and BRUCE B. COLLETTE' 



ABSTRACT 



Stomach contents of 395 longline-caught specimens of Thunnus (281 T. albacares, 52 T. t. 

 thynnus, 48 T. alalunga, 14 T. obesus) and 89 Alepisaurus were examined. About 45% of the tuna's 

 food, by volume, was composed of fishes, 35% of cephalopods, 15% of crustaceans, and 5% of mis- 

 cellaneous items. Fishes eaten by tunas ranged in length 9-360 mm SL (i 65 mm) and represented a 

 minimum of 88 genera in 58 families. Fishes eaten by Alepisaurus were 8-846 mm SL (x 98 mm) and 

 represented 40 genera in 34 families. Most forage fishes were immature forms of midwater and shore 

 fishes, many of which are associates of the pelagic Sargassum community. Ten of the most frequently 

 occurring families in Thunnus and Alepisaurus stomachs were Bramidae, Alepisauridae, Balistidae, 

 Paralepididae, Scombridae, Sternoptychidae, Carangidae, Tetraodontidae, Gempylidae, and 

 Syngnathidae. 



Cephalopods were the most frequently occurring (80-90%) invertebrate group in the tuna 

 stomachs, particularly the squid family Ommastrephidae. Crustaceans followed the cephalopods in 

 frequency of occurrence (30-80% depending on tuna species). Larval decapods and hyperiid amphipods 

 were the principal groups of crustaceans. In Alepisaurus stomachs, cephalopods occurred with 50% 

 frequency, usually octopods and soft-bodied squids, families Cranchiidae, Histioteuthidae, and 

 Bathyteuthidae. Crustaceans were present in 75% of Alepisaurus stomachs. Fewer decapod larvae 

 were found than in the tunas, while amphipods were found more frequently. Pelagic polychaetes 

 (Family Alciopidae), not found in any tunas, occurred in 38% of Alepisaurus specimens. 



Differences in the relative importance of particular forage categories in the diet of different 

 species of Thunnus and between the diets of Thunnus and Alepisaurus suggest interspecific 

 differences in feeding, either anatomical (i.e., relative predatory ability) or behavioral, particularly 

 the relative swimming speeds and feeding depths of different predators. The small-mouthed tunas 

 consumed generally smaller prey fishes (i-98 mm SL) than did the large-mouthed lancetfishes (x 240 

 mm SL). Smaller sized yellowfin tunas generally consumed smaller prey than did larger yellowfins. 

 Differences in swimming ability between tunas and Alepisaurus were reflected in the larger number 

 of swift-moving muscular squids eaten by the tunas. Composition of the forage indicated that T. 

 albacares fed at shallower depths than the other species of Thunnus and that Alepisaurus fed at 

 greater depths than any of the tunas. 



INTRODUCTION 



In the past 20 yr, the tunas have become objects of 

 intensified commercial and recreational fisheries. Heavy 

 utilization of these fishes and subsequent concern about 

 the limitation of stocks have made an understanding of 

 their biology increasingly important. Because the tunas 

 are peak predators in a vast part of the epipelagic zone, 

 one important aspect of investigation is their feeding 

 habits. Numerous forage studies have been carried out in 

 all parts of the world for the tunas of the genus Thunnus 

 and the skipjack genus Katsuwonus. Most information 

 has been reported on a qualitative basis, however, and 

 many studies have been based upon small samples. For 



'Systematics Laboratory, National Marine Fisheries Service, NOAA, 

 National Museum of Natural History, Washington, DC 20560. 



! Present address: Pacific Marine Environmental Laboratory, NOAA, 

 University of Washington, WB-10, Seattle, WA 98195. 



'Smithsonian Oceanographic Sorting Center, Washington, DC 20560. 



the Atlantic Ocean, Dragovich (1969) reviewed the im- 

 portant literature on tuna feeding habits published until 

 that time. Since then, several important contributions 

 have been added for the Atlantic: Dragovich reported on 

 the food of skipjack and yellowfin tuna in the Atlantic 

 (1970a) and the bluefin tuna in the eastern tropical 

 Atlantic (1970b); Dragovich and Potthoff (1972) com- 

 pared the food of the yellowfin and skipjack off the coast 

 of West Africa, and Borodulina (1974) reported on the 

 feeding of bigeye tuna in the Gulf of Guinea. 



Literature on Pacific tunas has not been similarly 

 summarized. Important contributions include in- 

 vestigations on the feeding of yellowfin in the central 

 Pacific (Reintjes and King 1953) and the comparison of 

 the food of central Pacific bigeye and yellowfin (King and 

 Ikehara 1956). Alverson (1963) compared the forage of 

 yellowfin and skipjack in the eastern tropical Pacific. 

 Iversen (1962) studied the food habits of albacore in the 

 central and northeastern Pacific. Iversen (1971) reported 

 on albacore and Pinkas (1971) reported on bluefin 

 feeding habits in Californian waters. 



