(b) 160° to 170° E. longitude 



The data from inveatigatlona in this aection are aummarized in table 103. 



Table 103. — Fiahlng conditiona from 160° to 170° E. 

 (35° to 40° N.) 



The overall average catch rate ia quite high, being alightly leas than 12.4, The moat 

 important element in the catch ia the albacore, which makea up more than 94 percent of the 

 total catch. Next moat important ia the bigeye tuna, which is 4.4 percent of the total catch. 

 Spearfiahes are extremely acarce, their catch rate being leaa than 0.2. Black tuna and yellow- 

 fin are alnnoat entirely without aignificance aa objectives of the fishery. 



If this ia compared with the above-deacribed aection between 150 and 160 E, , 

 which adjoina this aection on the weat, there ia a rather conepicuoua decline in the black tuna and 

 yellowfin, and something of an increase in the catch ratea of bigeye tuna. The increase in the 

 albacore catch rate is extremely conspicuous, the catch rate in this sea area being 7 times that 

 in the area described above. The spearfish catch rate has decreased sharply, being only one- 

 ninth what it was in the previously described sea area. 



o o 



Comparing this area with the aection 30 to 35 N. 



160° to 170° E. 



which adjoins it 



on the south, black tuna and yellowfin are rather conspicuously scarcer in this sea area, but 

 otherwiae, although there are aome differencea in the catch ratea, the composition of the catch 

 is very similar, showing that this area is more closely related to the area to its south than to 

 the section to the west. 



If we look at these phenomena without taking into conaideration the factora to be 

 diacuaaed below, it appeara that In the aea areaa north of 30 N. latitude the diatribution of the 

 tunaa and apearfishes which are taken by the tuna longline fiahery does not differ greatly with 

 latitude, that ia from north to aouth, but variea moatly with longitude, that ia from eaat to weat, 

 with a distributional boundary in the vicinity of 160 E. Of course this does not mean that the 

 pattern of distribution in a north-south direction is completely identical throughout the year. One 

 can detect marked seasonal changes from north to south, but these are mainly time lags and do 

 not have the character of complete differences between regions in the conriposition of the catch at 

 the same season. 



The first cause of marked differences in the composition of the catch at different 

 longitudes is differences in oceanographic conditions. In the sea areas adjacent to Japan the in- 

 fluences of the Kuroshio and the Oyashio work strongly, and the effects of the Kuroshio extend 

 much farther north than they do to the eastward in the central part of the Pacific, The Oyashio 

 extends here and there In wedges into this current. To the eastward the oceanographic conditions 

 are generally uniform, with the isotherms lying approximately along the parallels of longitude. 

 It goes without saying that this situation has a great effect on the distribution of the fishes dis- 

 cussed above. However, as the discussion of the distribution of these fishes hcis been baaed upon 

 the catch ratea of the longline fiahery, we muat take account not only of theae differencea in the 

 oceanographic conditiona but alao of differencea in the conatruction of the fishing gear and the 

 bait that is used. 



130 



