The distribution of the Albacore in the North Western Pacific extends from the Equator area to near the Polar Front area. However the fish distributes in such vast area, the fishing grounds are limitted almost in the seas between the Subtropical Convergence and the Polar Front, namely in the waters of the North Pacific Current and the north part of the Kuroshio Current.
This fish is caught mainly by the rod and line with live baits in the season between the Spring and Summer, but it is caught mainly by the long-line in the season between the late Autumn and the early Spring. The fishing grounds in the former season moves from south to north, and on the contraly, the grounds moves southward from nearly 40°N to as far as 27°-28° N in the latter, and then seem to turn back.
The present author attempted the analysis of the size composition of the fishes which are caught in the latter season, and obtained the result as following.
1) Six different size groups appear in every year. When these six groups are hypothesized to corrospond to each other in every year, the modal lengthes of the five seasons between 1948 and 1952 are placed with nearly the same intervals as ca. 57cm, 67cm, 78cm, 89cm, 100cm, 110cm.
2) Two groups with the modal lengthes 78cm and 98cm, are far more abundant than the others. So far the data obtained, it is clearly recognized that these two dominant groups appear alternately in every other, namely group with the modal length of 78cm are most abundant in the even number years and the other in the uneven number years.