To sum up the foregoing j, each of the schools which passes 

 through the Satsunan and Zunan sea areas to come into the North- 

 eastern Sea Area belongs to a group of schools which moves from 

 south to north in spring and ear'ly summer j and returns to the 

 south again in late summer and early aufumno Ihese fish are 

 thought to belong to two great migratory groups yihich. have their 

 origins in the Satsunan and Zunan areas and which are^, for the 

 most part, made up of mediiom-sized skLpjacko 



In addition to these widely migrating schools there are 

 thought to be others, made up for the most part of large and 

 small skipjack, which remain in the southern sea areas as local 

 groups of schools, making small migrations centered around 

 islands and shoals o In other words « it is believed that the 

 schools which make long migrations to the north and those which 

 make short migrations in the south meet in the vicinity of the 

 Zunan Sea Area, the former being composed chiefly of medium- 

 sized skipjack while -the latter is made up principally of large 

 and small fisho 



The skipjack which migrate into the Northeastern Sea Area 

 are chiefly those in the prime of maturity, and it is thought 

 that the pursuit of feed is the main objective of their migra- 

 tion to the northo (Ihis in view of the fact that iiie spawning 

 grounds and the nursery grounds for the juvenile fish are in 

 the warm-water areas of the southo) The rout© of their migra- 

 tion, judging from the movements of the fishing grounds, bears 

 a close relationship to the extension of the warm current and 

 its brancheso It is believed that the center of the fishing 

 grounds moves in the direction of the locus of the most curved 

 portion of the isotherms of the warm current systemo Even in 

 the case of "descending skipjack" the path of the migration 

 is probably determined chiefly by the patterns of withdrawal 

 of the branches of the warm- current and extension of the cold 

 ciirrents to the southo From this point of view it seems 

 appropriate to believe that there are two routes for the 

 descending skipjack^, one close to shore and the other farther 

 out to seao "Hiis is in fact the casso 



It is believed that there are no skipjack which remain 

 throughout the year in the waters off the Sanriku region = 

 This is indicated by the fact that the high-temperature water 

 areas with temperatures of 20° or higher^ where skipjack 

 fishing grounds occur in the summer off ^e Sanriku region^ 

 change for the most part in the winter to cold-water areas 

 having temperatures of less than ^° ^ Such a change in hydro- 

 graphic conditions would probably be difficult for a warm- 

 water fish like the skipjack to endure, and it is presumed to 

 be iinsuit^le for spawning and the growth of juvenile fish„ 



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