summer in eome numbers in the shallow waters surrounding the Bonln and Izu islands and in 

 the Pacific waters off Japan. About August the fieh begin their return journey southward. 

 Since a few yellowfin tunas are taken by long lines from deep waters near Japan during the 

 winter months, there is some Indication that certain of these fish remain in the northern 

 regions throughout the yenr. 



4. Oceanographic Data 



In Japanese waters the yellowfin tuna has been taken by long line when surface 

 water temperatures ranged from 14°C to 27'^C (Tsikayama and Andoi 1934, pp S, 20). The optimum 

 temperatures for greatest catch were at 21 °C and 22°C. 



Research and survey ships operating in the southern seas have been concerned only 

 with determinirg the major fishing grounds for the yellowfin tuna. Water current, temoera- 

 ture, transparency, and other oceanographic factors as they relate to thlw epecles have been 

 recorded Incidentally. The data obtained by the research vessel Zuiho Maru, operated by the 

 Govrrnment General of the South Sea Islands between 1938 ar.d 1940, are the only iiiformatiiin 

 available to this writer at present. These data point out that the best yellowiin tuna 

 fishing grounds are in the narrowest portion of the Equatorial Counter Current and at the 

 places where this current miies with the equatorial currents adjacent to it (compare Figures 

 2, 3, and 12). The best catches were made when the velocity of the surface current was 0.5 

 to 1.0 sea miles, the transparency of the water was between 25 and 35 meters, and the water 

 temperature from the surface to a depth of 100 meters was over 20°C. 



5. Habits 



When in Japanese waters during the summer months the yellowfin tuna swims near the 

 surface of the sea and approaches close to laiid. Small, immature fish about two kilograms 

 in weight are often found in the offBhor*" grounds accompanying schools of skipjacks. In the 

 southern regions, the majority of the yellowfin tunas caught have been taken from depths be- 

 tween 75 and 100 meters. 



Klshlnouye (1923, p 448) stated that the food of the yellowfin tuna was flying fish, 

 coffer fish, and eome deep sea species, besides calamaries, pteropods, heteropods, Uyperima 

 amphipods, larval and immature Squilla, megalops of crabs, etc, all typical food of a pelagic 

 species. An analysis of the stomach contents of 401 yellowfin tunas taken by long line east 

 of the Philippine Islands indicated that the food of the species in these waters was chiefly 

 cuttlefish, followed in order of importance by unidentified fish, file fish, Leiognathus , 

 shrimp, stomatopods, and puffer fish (Kanamura and Yazaki, 1940, pp 29-37). 



6. Seonomics 



The flesh of the yellowfin tuna is compact and pink in color. Because of its 

 excellent flavor when eaten raw, it is in much demand for "sashimi". Snail imrcature fishes 

 are often boiled, then smoked and dried to make a product known as "fushi". The meat of the 

 yellowfin tuna when canned becomes slightly dark suid is known as "light" meat tuna, in con- 

 trast to the "white" meat tuna of the albacore. As a potential export Item it ranks second 

 to the albacore. 



TUHA FISEIMG VESSELS 



Two main classes of vessels have been constructed by the Japanese for the tana fish- 

 eries. Since the fishing techniques used are specialized, these boats have developed into 

 highly distinctive types which are easily recognizable. 



Skipjack Vessels for Surface Fishing: The species most commonly taken by these 

 vessels is the skipjack. Small albacore, yellowfin tuna, and big-eyed tuna are sometimes 

 caught when found feeding on the surface. Pole and line, employing live bait or a Jig as a 

 lure, is the gear used by these vessels. Skipjack vessels are characterized by the presence 

 of a fishing platform, bait tanks, and a spraying apparatus (Figure 13). 



3? 



P-6307 



