is the beginning of a completely new movement of the albacore. This 

 group of fish cannot be said to be concentrated, but it is thought to have 

 an important meaning ecologically as a link between the populations dis- 

 tributed north and south of the Subtropical Convergence. Although the 

 northern group (the albacore schools distributed on the north side of the 

 Subtropical Convergence) has stopped its southward movement between 

 140 E. and 155 E. , a pairt of this group at this season continues to move 

 south and breaks through the Convergence into the sea areas to its south, 

 so that we find recorded occasionally catch rates of about 1,0 in the area 

 of 20°N. to 27°N. or 28°N. We have hardly any data east of 155°E., so 

 the movements in this area are not clear, but judging from the conditions 

 in April, May, and June it is thought that probably part of the fish continue 

 moving south after the main group has stopped its southward migration, 

 just as was the case between 140°E. and 155 E. 



1. Grounds North of the Subtropical Convergence 

 (1) North Pacific Ground 



The southern edge of the fishing grounds, just as in February, is 

 along the line of 26 N. to 27 N.,with absolutely no southward movement 

 shown. In April the fishing grounds show some northward movement, so 

 the position of the southern edge in March represents the farthest south 

 position of the North Pacific fishing ground. At this season the position 

 of the Subtropical Convergence between 140 E. and 170 W. is between 

 22 N. and 24 N. Consequently, this means that the North Pacific fishing 

 ground, at the time of its farthest south movement, is still on the north 

 side of the Convergence. There are a number of things to be thoroughly 

 considered in connection with the proposition that there is a deep relation- 

 ship between the oceanographic conditions eind the line on which the south- 

 ward movement of the albacore stops: 



(1) This line is approximately parallel to the Subtropical Convergence. 



(2) It appears to be in the vicinity of the boundary betweenthe easterly 

 flowing portion of the North Pacific Current and the countercurrent portion 

 on its south side. 



o o 



The intrusion of the Kuroshio between 140 E. smd 150 E. shows a 



decline in strength as compared with February, with its head pushed down 

 by the Oyashio so that the 18 to 20 C. isotherms are compressed from the 

 north southward and throughout the North Pacific fishing ground as a whole 

 are distributed in close proximity to each other between 28 N. and 31 N. 



97 



