Figure 1. --Average distribution of 

 isotherms (from data of the Tohoku 

 Region. Fish. Research Lab.). 



longline fishing ground for albacore. 

 In April it has already been noted that 

 there was quite active longline fishing 

 around 30 N. for the northward-moving 

 albacore, but in spite of this in May 

 there is a very sudden cessation of 

 fishing operations. We have only scat- 

 tered data from the sea areas between 



o o 



28 N. and 35 N. , and although these 



data show occasional cases of catch 

 rates of 1. in this area, the albacore 

 catch as a whole is much less than in 

 the preceding month. It is thought that 

 the albacore, which in April still 

 occurred in a considerable density, 

 have either suddenly moved north or, 

 if they are still present, they have 

 ceased to become an object of the long- 

 line fishery because of some extraor- 

 dinary change in their ecology. Judging 

 from the fact that simultaneously with 

 the ending of the longline fishing it is 

 replaced by an increasingly active pole- 

 and-line albacore fishery, one is inclined 

 to think that at this season, because of 

 some change in ecological conditions, 

 the fish have just ceased to be available 

 to the longline fishery. 



Figures 2 and 3 show by 10-day 

 periods the distribution of the albacore 

 pole-and-line fishing grounds in 1951 and 1952. In both years the pole-and- 

 line fishery began in the eastern part of the Kinan Sea Area. With the pro- 

 gress of the fishing season the fishery moves to the northeast, and the first 

 grounds to disappear are those west of the Izu and Ogasawara archipelagoes, 

 while operations continue the latest in the vicinity of 35 N. , 150 E. , or even 

 farther to the north. The direction in which these fishing grounds move is 

 exactly the opposite to that taken by the albacore which, after their appear- 

 ance west of 150 E. in October, moved south until March. The size com- 

 position of these fish for 1951 is shown in table 1. 



When we consider the movements of the albacore in April, it appears 

 that they begin to move north simultaneously from east to west across the 

 Kinaji fishing ground and the North Pacific fishing ground. The fact that, 

 in spite of this, we see no pole-and-line albacore fishing in the areas east 



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