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Table 111. --Fishing conditions by months (40 to 43 N. , 



150° to 155° E.) 



They have been omitted from the table, but bigeye tuna and albacore were only taken 

 in October. Among the spearfishes, striped nnarlin were extremely scarce in both months and 

 were quite vestigial, but broadbill were rather numerous and had a fairly high catch rate in 

 October. However, they seem to have declined sharply in November. The sharks on the contrary 

 showed a marked increase in their catch rate to 9. 3 in November. 



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If this is compared with the area of 40 to 43 N. 



140° to 150° E. 



which lies 



adjacent on the west, there was a considerable number of black tuna taken in October with a 

 catch rate of 0. 37 in the area of 140 to 150 E. However, in this sea area none of these fish 

 were taken at all. Few bigeye and albacore were taken in either area, and these species appear 

 to have almost no significance in the catch. Of the spearfishes, in October in the area of 140 to 

 150 E. the striped marlin (including black marlin and white marlin) had a catch rate of 0. 13 and 

 made up 30 percent of the totzil spearfish catch. In November they declined sharply, the catch 

 rate was only 0,02, and they made up only 3 percent of the spearfish catch. However, in this 

 sea area the proportion of striped marlin in the catch is very small in both October and 

 November. These phenomena probably nnean that the two sea areas have a quite different charac- 



ter as fishing grounds. Comparing this area with the area of 35 to 40 N 



150° to 160° E. 



which adjoins it on the south, in both October and November the catch of yellowfin, bigeye, and 

 cilbacore in the latter area is much greater than in this area, as is the catch of spearfishes. As 

 for the proportion of striped marlin and broadbill, in this sea area broadbill make up almost all 

 of the catch in both nnonths, while in the area of 35 to 40 N. , 150 to 160 E. in October the 

 striped n-iarlin are slightly under 89 percent of all spearfishes and in December they are'still 

 more thjin 50 percent. 



From the foregoing it is thought that this sea area differs somewhat in its character 

 as a fishing ground from the sea areas surrounding it. In effect, this sea area is outside the 

 range of distribution of most of the tunas and spearfishes or is at their extreme northern limit, 

 and therefore only a vestigial distribution is indicated or the fish do not occur at all. Fishing 

 seasons, as far as existing data show, are extremely short and the important species in the catch 

 are limited to the broadbill and sharks. 



VI. The Distribution of the Tunas and Spearfishes as Shown by Their Catch Rates 



The preceding chapters have presented a discussion of the significance and 

 characteristics of various sea regions as fishing grounds, based on data gathered by research 

 vessels in the past. Thus the general outline of the distribution and seasonal changes in catch 

 rates for tunas and spearfishes has already been set forth. The present chapter is an attempt to 

 bring together and summarize the various facts concerning the distribution of tunas and spear- 

 fishes in the western Pacific Ocean. 



The first question is what are we going to use as a criterion for determining the 

 presence or absence of these fishes? It is, of course, impossible to observe their occurrence 

 directly as in the case of land aninnals and plants. Consequently their presence can only be 



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