neighboring branch lines. The sharks are extremely sluggish and swim 

 about quite calmly and quietly, (Figure l) 



III. Distribution and Migration 



A. Horizontal distribution 



When it comes to distribution, direct observation is impossible 

 so it must be deduced from the catch of the fisheries. 



a. Outline of the distribution in Japanese waters 



These fishes are pelagic in nature and although they may when young 

 live along the coasts to some extent, in general their growth and re- 

 production take place in offshore v/aters. Since they are essentially 

 fishes of the tropical and subtropical seas, they occur throughout the 

 year in the waters of the low latitudes, hut they appear only seasonally 

 in the seas of the high latitudes. 



Through the spring and summer, as the water temperatures of the 

 Kuroshio gradually rise, these fish move northward along the current. 

 First come the black tuna, then the spearfishes appear vdth the albacore 

 shovdng up in the offshore waters at about the same time, and then the 

 yellowfin and the big-eyed tuna follow. 



The speed of migration is rather fast, for example, a black tuna 

 which is off southern Kyushu in February or March -.■/ill already have 

 reached the waters off Sanriku or Hokkaido in the latter part of June. 



In Formosan waters all species except the black tuna are present to 

 some extent the year round. In the Pacific coastal waters, or in other 

 words, in the current area of the Kuroshio, when the northeast monsoon 

 begins to blow in October the Trigratlon of the spearfishes bpgins ^-nd the 

 harpoon fishery continues until April nf the following year. The fishing 

 grounds are for the most part within 30 miles of thr coast. The schools 

 move gradually fro-^ south to north, but the speed of this movpment Is 

 extremely slow and at the_end of the fishing season the schools have 

 reached the vicinity of Hokasho. Throughout the fishing se--ison white 

 marlin //¥. marli'^a /are most abundant, while the nu^nber of trne mrTlin 

 / M. mitsukurii / increases in the middle of the season and the number of 

 black marlin / M, mazara /increases towards the end of the season. 

 Around December ''■he short- nosed marlin / Tetrapturus angustirostrls_7 

 occurs abundantly in offshore waters centered 150 miles from the coast. 

 The sailfish /^ Istiophorus oricntalis yoccurs densely for a few months 

 centered around June. Yello-TCia_are comparatively fetir, big-eyed tuna are 

 rather abundant, and koshinaga / N„ rarus _7 are most numerous during the 

 season of the northeast monsoon. Black tuna / T. orientali s / appear 

 from April to June, as set forth belov/. 



The northeast monsoon season is also the fishing season in the South 

 China Sea area. In tho early part of the season generally fishing is 

 most active in the southeastern part, that is, in the area adjoining the 



15 



