season some large fish had been biting on the hooks and breaking the branch lines so that year 

 they strengthened the fishing gear and for the first time took black tuna. Judging from the 

 mjinner in which young black tuna appear from summer to autumn along the coast of Japam, it has 

 been believed for many years that there was ample possibility of the occurrence of this species 

 in this area. 



A tendency has been seen for the black tuna season in the South China Sea area to 

 become gradually earlier with the passage of the years, but in ordinary years the species begins 

 to be taken around the middle or latter part of March and the fishery gradually becomes more 

 active with the passage of time, reaching its peak during approximately 1 month from the middle 

 of April to the middle of May. Thereafter the fishing gradually falls off until almost no black 

 tuna are taken in the early paxt of June. Around the end of the fishing season in most years some 

 fish axe caught east of Formosa Jind in the Ryukyu area, from which it is inferred that there is a 

 rapid movement of the schools to the northward. 



The first catch is often made along the 100-fathom line in the vicinity of Platas 

 Shoal, after which it is said the fishing gradually shifts to the eastward. During the first 2 or 3 

 years after this fishery was started the grounds were confined to that part of the China Sea west 

 of the Bashi Strait and it was thought that in general the fish did not occur south of Lingayen Gulf 

 (16 N. latitude). However, with the passage of years the fishing grounds were extended to the 

 eastward and it was discovered that there were superior fishing grounds in the Pacific Ocean 

 east of the Bataan and Babuyan islands, while at the same time the grounds were extended to the 

 southwaurd along the east coast of Luzon until all of the waters east of Luzon north of 1 5 N. 

 latitude became fishing grounds. 



There are almost no data from surveys by research vessels in the South China Sea 

 and the East Philippine Sea, but catch rates recorded by the author aboard commercial vessels 

 and those obtained from data supplied by commercial vessels to the former Taiwan Government- 

 General show catch rates of 2. to 3. 0. As yellowfin and spearfishes were taken in addition to 

 black tuna, the combined catch rate for tunas and spearfishes was 6. to 7. 0. Accordingly it 

 may be thought that the longline fishery in the area where black tuna were the main object was 

 rather advantageous financially. Before the war fishing vessels from Kagoshima, Kochi, and 

 other prefectures operated in May and June fronn the waters east of Formosa to the coastal 

 waters of the Ryukyu Islands and produced a considerable catch. Since the war considerable fish- 

 ing has continued in this region. 



The black tuna of the South China Sea region are in general large in size, most of 

 those taJcen around the beginning of the season weighing 300 kilograms or more. Toward the end 

 of the season the fish gradually becomes smaller, but even so examples of fish weighing less 

 than 200 kilograms are rare in the catcK It bears no direct relationship to the fishery, but it is 

 known that at this season in this sea area the black tuna are spawning. 



This fishery was almost completely discontinued in the latter part of World War II, 

 and the post-war situation is completely unknown, so nothing can be said concerning the present 

 state of the tishery. It appears possible, however, to discern a number of phenomena which 

 make one wonder whether the black tuna fishery in this area may not be gradually declining. 

 What is meant here by a decline in th,e fishery is not due to any human cause, such as the opera- 

 tion of commercial fishing vessels, but to a change in the migrational pattern of the black tuna. 

 Investigations in this sea area by the Shonan Maru, Takao Maru, Zunan Maru (forme r research 

 vessel of the Okinawa Prefecture Fisheries Experiment Station), Kiyo Maru, the Gini Maru 

 (research vessel of Mie Prefecture), Koho Maru, and Haruna Mciru have been reported. Among 

 these are some data which it is already impossible to obtain, but those which rennain may be 

 summatrized to show the fishing conditions in this sea area as given in table 25. 



62 



