1- 

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IT 



X 



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I I I 



TT 



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I I I I I 



-o TOTAL 

 -6 STRIPED 



-a BLACK 



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around the Oklnawan archipelago differ 

 somewhat In the character of the 

 schools and of the fishing grounds, but 

 the discussion of these relationships 

 must wait upon more thorough research- 

 es to be cairried out in the future. 



North of 30° N. latitude the 

 catch of striped marlln drops off shar ply- 

 but off northeastern Japein they are 

 rather numerous from July to Septem- 

 ber and, as figure 31 shows, there is a 

 blunt peak in the catch rate curve in the 

 vicinity of 36° to 38 N. 



8 9 10 II 12 



As was shown in figure 31, 

 the catch rates for broadbill gradually 

 increase beginning at about 20 N. , 

 and around 30 N. they make up more 

 than half of the spearfish catch. As 

 wax stated in the chapter on fishing 

 grounds, the areas of high density of 

 occurrence are generally west of 160 

 E. and they decrease in abundance east 

 of this longitude. The center of the 

 fishing grounds is approximately at the 

 same location as the central fishing 

 grounds shown in the case of the alba- 

 core, and the movements of the fishing 

 with the seasons generally resemble 

 those of the albacore. The most important fishing season is almost entirely limited to the 

 winter hall of the year. Charts VI, f_to k show the movements of these fishing grounds from 

 October to March. 



Figure 36. — Spearfish fishing conditions by 

 months (25° to 30° N. , 130° to 

 140° E.) 



In the chart for October (f) the areas of fishing grounds of dense occurrence appear 

 at 40 to 42 N. , 149 to 154 E. , although a thoroughgoing comparison is impossible because of 

 the lack of data around the peripheral areas. Some areas of fairly high catch rates are also seen 

 to the southeastward in the vicinity of 36 to 39 N. , 155 to 156 E. Elsewhere there are 

 scattered areas of fairly high catch rates off Iwate Prefecture, in the southern Izu Islands, south- 

 east of Amami Oshima, and east of Formosa, 



In the chart for November (g) the fishing grounds have become conspicuously extended, 

 and catch rates of more than 0.5 are indicated for the area from 41 to 31 N. , 144 to 156 E. 

 Comparing this with the situation in October, the grounds of dense concentration have extended to 

 the west and south. There are no data for the waters around the Izu Islands, so no comparison 

 can be made with October. In the Okinawa region the areas of high catch rates have shifted to the 

 southwestward and appear off to the east and south of the main island of Okinawa. The fishing 

 grounds to the east of Formosa appear at the same positions as in October, but the catch rates 

 appear to have improved somewhat. Compared with the chart of the distribution of albacore 

 catch rates for November, the broadbill are shown to be abundant somewhat more to the north 

 and east. 



In the chart for December (h) the center of distribution is farther south than in 

 November in the vicinity of 55 N. amd areas with catch rates of over 1. are recorded from the 

 range of 35 to 40 N. , 150 to 152 E. Compared with November, the fishing grounds are ex- 

 tended a good deal to the southwest and areas with rather high catch rates appear from off BSsO 



163 



