It aa an Important article In thnlr diet and have considernd It a favored fiah. Xvldence 

 that the black tana was eaten by the ancient people has been unearthed during excavations 

 of shell mounds in the Eanto and Tohoku regions. Bones which are Identifiable as those of 

 the black tana were uncovered from these mounds. little exlstsi howaveri to indicate the 

 first fishing techniques used to capture these giant fish. Aathorltlee believe that huge 

 traps placed in shtdlow waters were the most primitive method by which they were caught. 

 Vfhen the fish entered theee traps they were either clubbed to death or speared and drawn 

 up on shore. Until comparatively recent times the black tuna was taken almost solely In 

 coastal waters by set nets which were a natural development from single traps. With the 

 introduction of motor-driven vessels It was possible to use other gear for taking blausk 

 tunas in the deeper offshore waters. Today the species is caught for the most part by set 

 nets located close to shore and by long lines in the deeper eea regions. 



Z. Dlagnostio Characteristics 



The black tuna (Figure 7) can be recogniced by the short tapering pectoral fin, 

 which scarcely reaches the origin of the second dorsal fin. and by the sharp upward bend of 

 the lateral line at a point above the origin of the pectorals. The lateral line then bends 

 gradually dovmward and posteriorly. The back is nearly black, changing to a grayish blue 

 with metallic reflections in the posterior part. The belly is grayish with many colorless 

 dots. In mature epeclmens these markings tend to disappear. The first dorsal and the ven- 

 trals are grayleht the second dorsal is grayish with a yellow tip, the dorsal finlets are 

 yellowt the aaal and the anal finlets are sllvery> and the pectorals are nearly blaok. 



Several differences between the Japanese species and the California bluef In tuna, 

 euch as color of the fins and ramification of the cutaneous blood vessels, were noted by 

 Kishlnouye (1923, p 440). However, detailed comparisons between these forms and the Hawaiian 

 and Australian common tunas have not been made, and the exact relationships of the various 

 geographically snpnrated Pacific units are as yet undetermined. 



The mature black tunas taken In Japanese waters generally weigh between 125 and 200 

 kilograms, but the species attains even more gigantic sizes. Klshinouye (1923, p 439) re- 

 ported specimens welding about 375 kilograms taken near Odawara in 1913, and more recently 

 (date unknown) a specimen weighing 450 kilograms was taken in Toyama Bay on the Sea of Japan 

 coast of Honshu. 



3. Distribution and Migration 



The distribution of the black tana Is known only from the areas In which commercial 

 operations take place. Therefore, Its known distribution is more indieatlTe of areas where 

 the fish tend to shoal or congregate, thus meklsg eomoeroial operations feasible, rather than 

 of true range. The fishing grounds in the northwestern Pacific Ocean extend from Sakhalin and 

 and the southern Kuril Islands south along both coasts of Japan and the Korean coast, through 

 the ^ukyus and the Bonins to the area between southern Formosa and northern Luzon (Figure 6). 

 Records show that in recent years black tunas have been obtained in offshore waters east of 

 Japan by long line vessels fishing primarily for albacore or swordfish (Kimara, MS). The 

 known distribution of the species has thus been extended, but its true range will not be 

 ascertedned until research workers begin critical compilation of all records obtained through- 

 out the western Paolfie. 



Data of value concerning the migratory routes followed by the bleick tuna in Japa- 

 nese waters are based solely on reports given by vessels as to seasonal changes In major fish- 

 ing grounds. Dr K. Kimara, of the Tokyo Central Fisheries Ibq>erlmental Station, Is now pre- 

 paring this material for publication. For Philippine waters, information has been supplied 

 by I}r H. Hakasnra, formerly of the Formosa Fisheries Experimental Station. 



As the black tuna Is found in the southern ^rukyus daring Jane and In the Tohoku 

 coastal region (northeastern Honshu) at the eame time, several races within the species are 

 postulated by Japanese scientific workers. Morphological analysis to support this belief 

 has not been atteipted, but a division Into Japanese and Philippine units appears to be valid 

 from the evidence at hand. The information presented indicates the complexity of the life 



19 



p-6307 



