Kornilov, Leo nova, Liubimova, Obvintsev, 

 Prosvirov, Sal'nikov, Terekhov, and Khromov, 

 1967; Sokolov, 1967a, 1967b. 



The numerical method (Legendre, 1934; 

 Bouxin and Legendre, 1936; Crane, 1936; 

 Legendre, 1940; Carlson, 1952; Morovic, 1961 ) 

 and the volumetric method (Postel, 1963; 

 Randall, 1967) were used in relatively few 

 studies. 



In the more detailed papers, usually one of 

 the number methods (the numerical or the 

 percentage method) was combined with the 

 volumetric method. 



In a study of blackfin and yellowfin tunas 

 near Bermuda and the West Indies, Beebe 

 (1936) used a number method in which he listed 

 the number of stomachs containing each par- 

 ticular food item-- sometimes he listed each 

 food item in each fish by number and some- 

 times he used percentages in summations of 

 broader categories, such as fishes and crus- 

 taceans. 



Various combinations of frequency-of-oc- 

 currence and volumetric, or weight, methods 

 have been used by several authors. Bane (1965) 

 evaluated the forage organisms of blackfin 

 tuna in the waters of Puerto Rico. Postel 

 (1955a) evaluated the food of Neothunnus alba- 

 cora (= Thunnus albacares ) in the eastern 

 tropical Atlantic. De Jager, Nepgen, and Van 

 Wyk (1963) reported on food of tuna from the 

 west coast of South Africa. Oren, Ben- Tuvia, 

 and Gottlieb (1959) described food of T. thyn- 

 nus . E. alletteratus , and T. alalunga from the 

 eastern Mediterranean. Penrith (1963) studied 

 the food of several species of tuna off the 

 Cape of South Africa. Sund and Richards (1967) 

 showed the distribution of forage organisms in 

 the Gulf of Guinea for yellowfin and skipjack 

 tunas for two different seasons; and Suarez- 

 Caabro and Duarte-Bello (1961) evaluated the 

 forage organisms of skipjack and blackfin tunas 

 in Cuban waters. 



Soviet scientists (Zharov, 1965; Sokolov, 

 1967b) often applied the points method (using 

 an arbitrary scale) to measure the degree of 

 fullness of tuna stomachs. 



RESULTS OF STUDIES 



The information in the reports reviewed was 

 divided into several major topics: food organ- 

 isms; tunas as collectors of marine organ- 

 isms; tuna feeding habits; food in relation to 

 species and size of tunas; and seasonal and 

 diurnal variations in tuna food and feeding 

 habits. 



Food Organisms 



I examined the combined data in the reviewed 

 papers from several points of view. It did not 

 appear that a quantitative treatment of the 

 data in terms of areal and temporal distribution 



would be particularly worthwhile, since many 

 of the original data were not quantitative. 



Comparison of tuna prey in the stomachs of 

 fishes caught by various types of gear can be 

 of considerable value in studies of food selec- 

 tivity (Blackburn, in press), but data in the 

 reviewed papers were insufficient for such 

 a purpose. My compilation is therefore re- 

 stricted to a taxonomic list of the food items 

 and a record of their occurrence. 



About 500 different forms were identified in 

 the tuna stomachs. Fishes were represented 

 by the greatest number of identified kinds (33 1 ), 

 crustaceans were second (111), and mollusks 

 were third (74). These numbers should not be 

 compared, since many organisms were identi- 

 fied only to genus or to family. The list of 

 identified taxa may reflect the rates of diges- 

 tion—the axial skeletons and scales of fishes 

 and the exoskeletons of crustaceans are less 

 subject to damage by digestive processes (and 

 therefore easier to identify) than are the 

 remains of fleshier organisms. Fewer speci- 

 mens of mollusks were identified than fishes 

 and crustaceans; most of the mollusks were 

 cephalopods, whose identifying external char- 

 acters are the first to be destroyed by the 

 digestive process. The list of identified taxa 

 also suggests that taxonomic work done on 

 fishes was more extensive than that on the 

 other two groups. 



Although most of the studies were qualita- 

 tive, a general pattern of feeding was evident 

 for all the species of tuna. Taxonomically, 

 food consisted mainly of fishes (63 percent of 

 the total taxa), crustaceans (21 percent), and 

 mollusks (14 percent). Tunicates (2 percent) 

 were present but were of minor importance. 

 Tuna forage organisms (as identified in the 

 original publications) and the species of tunas 

 in which they were found are listed in the 

 Appendix. Fishes are listed alphabetically; 

 invertebrates also are listed alphabetically 

 but are grouped under broad categories. 



Further considerations of the three main 

 categories of tuna food revealed that the fishes 

 eaten by tunas consisted chiefly of pelagic 

 juveniles and adults, but also included lar- 

 val forms and (occasionally) benthic fishes. 

 Crustaceans were largely macrozooplankton 

 (a great variety of larval decapods and stoma- 

 topods, and mostly adult hyperiid amphipods, 

 isopods, copepods, ostracods, euphausiids, 

 and mysids), and some micronekton (princi- 

 pally shrimp). Mollusks were mostly cepha- 

 lopods (principally squid), but heteropods and 

 pteropods were also prominent. 



A practical aspect of studies of food organ- 

 isms is the definition of a relation between the 

 areas of food abundance (or areas of high 

 biological productivity) and tuna abundance. 

 Although the food chain in the ocean has been 

 studied to some extent (mostly the relation 

 between primary and secondary producers 

 and large carnivores), data from the Atlantic 



