We have very few data on the size composition of these albacore 

 and can therefore give no detailed analysis, but average weights of 5. 95 

 kan /50 IbsfJ (based on measurements of 10 fish) at to 20N. , 150 E. 

 to 16'0°E. , and 6. 8 kan /56 lhs_^J_ (based on measurements of 8 fish) at 

 10°N. to 12°N., 170"W.~to 180^, show that at this season the albacore 

 south of 10 N. are smaller than those occurring north of that latitude. 



APRIL 

 General 



In April the aspect of the fishing grounds changes completely. 

 This is the season of change from the winter-type to summer -type fishing 

 conditions, and it is just at this tinne that in the northwest Pacific Ocean 

 the changeover occurs from the season of northwesterly winds to that of 

 southeasterly winds. Comparing the winter-type fishing conditions (during 

 the period of northwesterly seasonal winds in the northwest Pacific) and 

 summer-type fishing conditions (during the period of southeasterly seasonal 

 winds in the northwest Pacific), the summer-type fishing conditions are, as 

 a rule, extremely inactive as far as longline fishing is concerned, in conn- 

 parison with the winter-type fishing conditions. Furthermore, on some 

 fishing grounds the character of the population is in sharp contrast, as 

 between these two seasons. At the height of the season of northwesterly 

 winds, from November to February, albacore fishing is active simultane- 

 ously on all fishing grounds regardless of whether they are north or south 

 of the Subtropical Convergence, and at times the albacore fishing is even 

 quite good in South Sea areas. However, by February there are already 

 indications of a decline on all the fishing grounds, and this time corres- 

 ponds to the end of the season of northwesterly winds. In March the South 

 Sea fishing grounds disappear and the grounds north of the Subtropic al 

 Convergence cease their southward movement. (We have no detailed knowl- 

 edge of what happens on the Okinotorishima fishing ground because of inade- 

 quacy of the data, but it is a fact that the fishing drops off. ) In April the 

 grounds north of the Subtropical Convergence begin moving north, in a 

 direction opposite to their movements under the winter pattern. Longline 

 fishing operations cease in April and pole-and-line catches begin to be made. 

 Also, we begin to see southward migrations of large albacore, which have 

 separated off from the populations „on the grounds north of the Subtropical 

 Convergence, something which was never seen in the winter-type fishing 

 situation. There is still a considerable occurrence of albacore in the 

 Okinotorishima ground, but on the other grounds they have completely 

 disappeared. 



Thus the albacore fishing conditions make a complete change with 

 the month of April as the dividing line. 



112 



