All information is taken from Alain Fonteneau's "Atlas of tropical tuna fisheries", ORSTOM, 1997
These show monthly catches at surface caught by rod and line and those deeper caught by long-line. The Japanese area is KURO/NSPT.W. The surface catches peak in summer and are nearly all skipjack with some albacore. The longline catches peak in late winter with a mixture of albacore, bigeye, albacore and swordfish. The bluefin share of the catch is negligible in winter but increases in summer.
These results are confirmed by the maps shown below. Most of the surface catches are skipjack with some albacore. The main catches are in the second and third quarter.