resident group is fished principally in the area around the 

 small isles and over the shallow bankSo l>ie resident group is 

 also related with small isles of t'?- Bonin Chain, although it 

 can migrate north-eastwards into the open sea of the Tohoku 

 tegiono On the other handj the migratory groups are fished in 

 any portion in both regions,, (U) Ihe migratory shoal of Ill-year 

 group in the Tohoku region is probably originated from the migra- 

 tory shoal of Ill-year group in the Liu=Ciu region^ because 

 shoal of similar character to those in both regions can be fished 

 in the Seinan regionc The migratory shoal of Ill-year group can 

 be called the Iau=£iu group both in Seinan and Tohoku regions » 

 While, the resident groups in both regions show no similarity in 

 any respect to each othero In additionj, no resident shoal is 

 fished in the Seinan region between these two regions o According 

 to the distribution of the fishing positions^, the resident shoal 

 seems to migrate into the Tohoku regions from the southern sea 

 through the Bonin Chain, Therefore the resident shoal can be 

 considered as the Bonin group in the Tohoku region o The migra- 

 tory shoal occiipies 6O5S of total catch and the resident shoal 

 kO% in the Liu-Kiu regiono In the Tohoku region^, the Liu-Kiu 

 grovp occupies 80^ of total catch and the Bonin group only 20^ o 

 ($) The fluctuaiion in the yield of these regions seems to be 

 influenced by the changes in the age composition in the Liu-Kiu 

 region^ and also in the ratio of tiie resident group (the Bonin 

 group in the Tohoku region) to the migratory group (the Liu-Kiu 

 group in the Tohoku region) o 



(end of English synopsis) 



Since 19 3h the Central Fisheries Experiment Station has 

 been carrying on a study of the skipjack catch in congunction 

 with the fisheries experiment stations of tiie various prefectures,, 

 In order to study the causes of fluctuations in the catchj it is 

 necessary to assemble statistical data and also to learn the 

 biological characteristics of 1±ie fishj, such as life history, 

 migrationsg age composition of the schoolSs and the types of 

 schools o As preparation for the catch study the age of the 

 skipjack was determined using vertebrae and the age composition 

 of the catch was found, 'and deductions were made as to what 

 kind of biological groups compose the skipjack population of 

 the Pacific coast of Japano 



The Skipjack Schools of the Ryukyu Sea Area 



lo Body-length distribution. The skipjack of this sea 

 area are dTvided into three categories by size^ large, medium^, 

 and small o In the catch of the Hyuga Maru, the Shoyo Maru, and 

 the Zunan MarUo which fished in this area in 193Us, there was a 

 mixture of large, medium, and small^sized fish, with large and 

 small fish plentiful while medium-sized fish were few (table IJo 



3U 



