西南太平洋10°S附近の鉛直海洋構造とビンナガ漁況
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概要
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Except for assumptions advanced by SVERDRUP et al (1952) and NAKAMURA (1954-55), no attempt has ever been made at throwing light upon oceancgraphical conditions in the general vi-cinity of Lat. 10°S in the Western South Pacific. In the present study the author discussed vertical structure of the waters in this region using results from the observations carried out by the Kuroshio-Maru No. 3 in June 1953 (YAMANAKA, unpublished) and the Daifuji-Maru in January 1955 (SUZUKI et al). In addition, previous data obtained by the Carnegie in Novem-ber 1928 (SVERDRUP et al, 1945) and the Hugh M. Smith from January to February 1951 (CROMWELL et al, 1954) have been made use of (Fig. 1). On the basis of those data fishing conditions for albacore (KAMIMURA and HOMMA, unpublished) have been examined to see what relationships they have with the oceanic structure in the region during the fishing seasons from January to February and June to July. However, scarcity of comparable data has made the author introduce in his study a hypothe-sis that hydrographical fluctuations between years and from one area to another may be negligi-bly small as far as the general locality under study is concerned. Findings from the study arc: 1) Data obtained by the Daifuji-Maru, the Carnegie and the H. M. Smith point to a discontinuity layer with considerable convergence which is found extending from east to west in the neighbourhood of Lat. 10°S during the months from November to following February (Figs. 2-5). In those winter months major fishing grounds for albacore are present in the waters south of Lat. 10°S, but practically no successful fishing in the north of the sea (Fig. 6-a). 2) However, the records available from the Kuroshio-Maru No. 3 for June and July do not indicate such a discontinuity layer as seen the winter months. Nevertheless, it is interesting to notice that in June and July fishing grounds with fairly high hooked rates extend over the sea north of the main fishing grounds still remaining south of Lat. 10°S (Fig. 6-b). These evidences seem to be suggestive that the area of discontinuity layer is playing an important part as a northern limit in the distribution of albacore living in the Western South Pa-cific.