fishing ground, can hardly be thought to be the only condition governing 

 that development. This, consequently, automatically limits the signi- 

 ficance which the surface water temperature can have as an indicator 

 in scouting for fishing grounds. In underteiking fishing operations in 



these waters in December it will be better to avoid water masses with 



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temperatures below 18 C. south of 35 N. , and north of that latitude it 



will probably be advantageous not to operate in waters with a tempera- 

 ture below 17 C. or above 20 C. 



II). Area of 150°E. to 160°E. 



This is the area of low catch rates between the waters west of 

 150 E. and those east of l60 E. The difference between the catch rates 

 in this area and in those adjacent to it on the east and west is extraordi- 

 narily conspicuous in October, but in Novennber areas of high catch rates 

 intrude from the east and west and the area of low catch rates is consi- 

 derably narrowed. In December the catch rates here are still lower than 

 in the waters to the east and west, particularly low catch rates being seen 

 in those sections running southwest from the vicinity of 40 N. , 155 E. 



Looking over this area as a whole, we find a row of unit areas 

 with coniparatively high catch rates running along its southern part; i.e., 

 along 30 N. In the northwestern part, also, north of 34 N. there is a 

 triangular area of high catch rates. Judging from the way in which the 

 fishing grounds develop from November on, the former section of high 

 catch rates is a prolongation of the waters east of 160 E. , while the 

 latter is probably an extension from west of 150 E. If we omit these 

 sections with high catch rates, throughout this area as a whole there 

 is a trend for the catch rate to be lower in the west and higher in the 

 east. This pattern probably is a result of the extension of the fishing 

 grounds westward from east of l60 E. 



The position at which the part with low catch rates appears shifts 

 east and west considerably from year to year, and these shifts appear to 

 parallel the movements of the North Pacific fishing grounds as a whole. 



Catch rates over this whole sea area are higher than they were in 



November. Between 29 N. and 32 N. unit areas with catch rates of 2.0 



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to 5.0 are lined up solidly. Between 32 N. and 37 N. , east of 155 E. , 



there are mainy catch rates of 1. to 3.0 and at times they go higher than 



5.0, but west of 155 E. , in general, the catch rates are low and there 



appears to be a wedge-shaped trough of low catch rates. 



As for the changes in the catch rates in the triangular area of high 

 rates in the northwest, the values increase just like those in the northern 



44 



