o 

 B. Grounds in Tropical Seas South of 10 N. 



o o 



Throughout the whole area from 130 E. to 170 E. albacore fishing 



is extremely inactive. Rare albacore catches are made along the boundary 



of the North Equatorial Countercurrent and the South Equatorial Current, 



but there appear to be almost no cases of catch rates higher than 0. 3. The 



fish are less than 6 kan /50 lbs. / in weight and thus smaller than those of 



the middle latitudes. 



MAY 

 General 



The albacore longline fishery has completely ceased to figure in 

 the general picture. The fishing vessels, which were still fairly active 

 in the preceding month in the North Pacific fishing ground, have almost 

 completely ceased to operate. About all that is left is the incidental catches 

 of albacore taken by longline vessels fishing for spearfishes in the mid- 

 latitude areas. On the other hand, this is the season when pole-and-line 

 fishing for albacore is gradually becoming active in the waters close to 

 Japaji, and thus the aspect of the albacore fishery is completely different 

 from what it was during the winter. 



(1) North Pacific Ground cind Kinan Ground 



Oceanographic conditions 



In April and May the oceanographic conditions on this ground are 



the exact opposite of what they were during the height of the longline fishing 



season up to March. That is, the isotherms which had been continuing to 



move south have now begun to move northward, and the Kuroshio, which 



was continuously declining in strength, is gradually strengthening. As 



figure 1 (distribution of isotherms on the average year's pattern, abridged 



frona data of the Northeastern Regional Fisheries Research Laboratory) 



shows, in April the isotherms begin a general northward movement, and 



in May the 15 C. isotherm runs east and west between 37 N. and 39 N. , 



while the 20 C. isotherm penetrates deeply to the northeast into the cold 



o 

 water mass east of Cape Nojima, its most advanced point reaching to 37 N. 



It will be noted that the northward movement of the 20 C. isotherm is more 



o o 



conspicuous than the northward shift of the isotherms from 10 to 15 C. 



The considerable revival in May of the Kuroshio, which around February 



and March was at an extremely low ebb, is well shown by the results of 



sectional observations 300 miles southeast of Cape Nojima in figure 3 for 



February. In May this sea area has lost its significance, at least as a 



120 



