Although abundant data arc available for Pacific 

 T. obcsus from 400 mm. and up (Dung and Royce, 

 1953), very few Atlantic s{)ecimens smaller than 

 1,000 mm. have been recorded. These data, never- 

 theless, indicate that the pectoral fin in Atlantic T. 

 obesus does not become as long as that of the Pacific 

 populations and that, in fact, the length of tliis fin in 

 Atlantic T. obesus approaches T. albacares more 

 closely than Pacific T. obesus at intermediate sizes 

 (050-1,000 mm). Some Pacific and Indian Ocean 

 specimens, however, have shorter pectorals than the 

 majority and overlap with Atlantic specimens (fig. 

 31). 





Figure 31. — Relative length of pectoral fin in Thunniis 

 obesxis. Dots, Indian and Pacific ocean specimens; open 

 circles, Atlantic specimens. 



It seems, therefore, that the Atlantic population 

 of T. obesus is differentiated from the Pacific popu- 

 lation, perhaps on a subspecific level, but much more 

 data on sizes smaller than 1 ,000 mm. will be neces- 

 sary to establish the level of differentiation. 



Range 



The distribution of T. obesus in the western Atlan- 

 tic, as summarized by Mather and Gibbs (1958), 

 includes the area from 42°18' N., 64°02' W. south 

 along the coast of the United States to Florida; 

 Bermuda; the Caribbean Sea around the West 

 Indies; south to Margarita Island, Venezuela (re- 

 ported as T. tJnjnnus by Fernandez- Yejjez and 

 Santaella, 1956, but considered to be T. obesus by 

 Mather and Gibbs). Xagai and Nakagome (1958) 

 reported T. obesus from the north equatorial and 

 Brazil currents off the coast of South America. In 

 the eastern Atlantic it has been taken off Portugal, 



Spam, tlie Azores, and Madeira, south to Angola 

 (Vilela and Monteiro, 1959) but it is absent from tlie 

 Mediterranean Sea. There is a report of its occur- 

 rence from the Gulf of Gascogne (Legendre, 1930), 

 but this needs confirmation. Talbot and Penrith 

 (1961, 1962, 1963) have shown the distribution to be 

 continuous arounil the tip of South .A.frica, but the 

 fish could originate either in the Atlantic or Indian 

 ocean. 



T. obesus, like T. albacares, is found throughout the 

 Indian Ocean from 20° N. to 30° S. (Mimura et al., 

 1963b). Its range in the western Pacific is also 

 similar to that of T. albacares, extending from about 

 40° N. to about 30° S. (Alverson and Peterson, 1963). 

 In the eastern Pacific it extends to 40° S. (Japan 

 Fishery Agency, 1965). 



THE BLUEFIN TUNA COMPLEX: 

 T. MACCOYII AND T. THYNNUS 



In recent years, various authors have attempted 

 to recognize as distinct species the populations of 

 bluefin tuna in Jajjan and the western Pacific {T. 

 orientalis), Australia {T. maccoyii), eastern Pacific 

 (T. saliens), western Atlantic (T. secunclodorsalis), 

 and eastern Atlantic {T. thi/nnus). Frade (1925) 

 noted that the eastern Atlantic form liad two 

 rows of cutaneous arterioles, whereas Kishinouye 

 (1923) pictured a single row in his Japanese speci- 

 men. Godsil and Byers (1944) found California 

 bluefin similar to Kishinouye's descriptions of the 

 form, except for two major characters. According 

 to Kishinouye, the swimbladder of the Japanese 

 form is short, broad, and heart-shaiK'd, whereas that 

 of California specimens "is rudimentary and of a dif- 

 ferent shape in small fish, and so erratic in large 

 specimens that no constant pattern is discernible" 

 (Godsil and Byers, 1944: 102). In California speci- 

 mens, there are two rows of cutaneous arterioles and, 

 according to Kishinouye, but a single row in Japa- 

 nese fish. Godsil and Ilolmherg (1950) described 

 numerous anatomical differences among California, 

 Australian, and western Atlantic specimens, finally 

 concluding that the Australian form (7'. maecoijii) is 

 distinct from the California and western Atlantic 

 forms {T. thijnnus) and that the latter are also dis- 

 tinct, but not quite so trcnchantl}'. On the basis of 

 published accounts of Japanese and eastern Atlantic 

 populations (Kishinouj'c, 1923; Frade, 1925), Godsil 

 and Ilolmberg tentatively concluded that eastern 

 and western Atlantic forms are conspecific but that 

 the Japanese form is different. On the basis of 



112 



U.S. FISH AND WILDLIFE SKRVICE 



