Studies on the Albacore-III

The area of the Kuroshio current or the North Pacific current is known as the quite excellent fishing ground of the Albacore. Albacore in this ground migrates southward during Autumn and early Spring, and is mainly caught by long-line. From Spring to Summer it migrates northward and is caught by rod and line with live bait. As to the former catch the author already reported it's size-composition1). In the present, the author reports the analysis of the size-composition of the latter. The principal informations obtained by this work are as follows. (1) Though the range of the size is confined within the limit between 50 to 100cm during the seasons of 1951 and 1954, there are the remarkable annual fluctuations. (2) The number of length-groups are not fixed by the seasons. 3 or 5 length-groups appear in each season from 1951 to 1954. (3) The modal length of each length-group shows remarkable annual fluctuation. (Table 1) (4) The relative abundance of each length-group is very unstable as shown in Table 2. In most cases, the most dominant length-group occupies the overwhelming proportion. Such a size-composition of the northward migrating Albacore differs from that of southward migrating one as follows. (1) Such advanced age groups* as seen in the sout ?? ward migrating fishes do not appear in these which migrate northward. (2) Size-composition of the northward migrating ones shows the remarkable annual fluctuation, therefore it is able to say that it is much more unstable than that of the southward migrating. (3) The dispersion of the length frequency of the northward migrating ones is much more small than that of the southward migrating ones. Then differences between the two groups seen to be based on ecological differences of them other than the difference of fishing method. In spite of these differences, the author hypothesized that there will be some relations between these two groups on a basis that the body-length of the most dominant size-groups are less than 100cm in both migrating groups. * Age is not determined, larger than 90cm.1)