catch rates are continuous from 140 E. westward to 134 E., and no 

 boundary is apparent between this fishing ground and the grounds east 

 of the line of islands. The southern limit of the fishing ground is in 

 the vicinity of 27°N. latitude and coincides approximately with the southern 

 limit of the North Pacific fishing ground. The northern edge is not very 

 clear, but it appears to be in the vicinity of the boundary between the 

 main current of the Kuroshio and its countercurrent. However, fairly 

 high catch rates are occasionally shown in the main current area. 



Considering now the oceanograhic conditions in this area, we 

 find that the main stream of the Kuroshio, which flows northeast directly 

 south of Honshu, is conspicuously narrowed here. A very clear clock- 

 wise gyre is formed on its south side. The southern limit of this gyre 

 is at 28°N. , and its eastern side impinges upon the current flowing north- 

 ward east and west of the Izu Shichito Islands, while its western and northern 

 sides are bounded by the main Kuroshio current. Figure 9 gives the results 

 of observations made 300 miles south of Shionomisaki in January 1936, the 

 left-hand graph showing the temperature and the right-hand graph the salinity. 

 The Kuroshio is conspicuously pushed in against the coast, and there is a 

 mass of low -salinity water between it and the gyre. Within the radius of 

 60 to 200 miles off the coast is the area where the gyre is clearest, with 

 its center in the vicinity of 120 to 150 miles off the coast and with the salin- 

 ity dropping toward its edges. Southof a point 250 miles out (at about 30 N. ) 

 we find the southern edge of the gyre, and in this section the temperature 

 and salinity are both rising, appearing to indicate a connection with the 

 source of waters in the Okinotorishima area. 



30 60 90 120 150 180 210 240 2r0 JOO 



JO 60 90 120 ISO 180 210 240 2T0 300 



Figure 9. --Results of an oceanographic section 300 miles due 

 south of Cape Shionomisaki in 1936. (From Semi-annual 

 Reports of Oceanographical Observations, Central Fisheries 

 Experiment Station. ) Left, isotherm distribution; right, 

 isochlors. 



The fishing grounds develop within this vortex area, and with the 

 passage of time they extend themselves to the westward. In January the 

 western edge of the fishing grounds is in the vicinity of 134 E. , but in 

 February it reaches the vicinity of 132°E. We can see many areas in 

 which catch rates of 3.0 or more are indicated, particularly in a row 



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