北洋漁場におけるベニザケ5<sub>2</sub>および6<sub>3</sub>年令魚の種族判別とその分布について

Abstract

Scales of adult sockeye salmon migrants were collected from 19 rivers along the coasts of the northern Pacific (Fig. 1). These scales were magnified 100 times and the scale character ‘FR’, distance between the nucleus and the last annulus of the fresh water zone along the symmetrical axis, was compared among these fish groups. From the comparisons of the scale character, the characteristic of Bristol Bay's race was established in both cases of 52 and 63 aged fish groups. Therefore, an attempt to estimate the percentage of the Bristol Bay's race of sockeye salmon in the western high sea area of the northern Pacific was done, and the following results were obtained. 1) Age of sockeye salmon caught in the western high sea area of the northern Pacific are 42, 52, 53, 62, 63, 64, 73 and 74. Among such aged fish, 52 and 63 aged ones are most abundant and totals of the fish of these two ages occupy more than 70 percent in every fish group (Table 1). 52 and 63 aged fish groups, therefore, were studied. 2) The mean values of the scale character ‘FR’ of the 52 aged sockeye salmon migrants collected in rivers are ranged from 0.37 to 0.49mm in fish groups of Bristol Bay and from 0.20 to 0.37mm in most fish groups of Asia and other two areas, Gulf of Alaska and America-Canada (Table 2, and Fig. 2, 3). Those of the 63 aged fish are from 0.57 to 0.69mm in fish groups of Bristol Bay and 0.35 to 0.53mm in most fish groups of the other areas. Therefore, the local race, Bristol Bay's one, can be recognized through its scale characteristics in both cases of 52 and 63 aged fish groups. 3) Frequency distributions of the scales character “FR” of groups of 52 aged sockye salmon caught in the western high sea area of the ocean contain some fish groups with larger mean values than 0.37mm, which are the characteristic of the Bristol Bay's race, and fish groups with smaller mean values than 0.37mm, which are the charac-teristics of fish of Asia and other two areas. On the other hand, frequency distributions of the scale character of groups of 63 aged sockeye salmon caught in the high sea are near the coast of Asia contain few fish groups with larger mean values than 0.57mm, which are the characteristic of the Bristol Bay's race, though those of fish groups caught in the mid ocean contain some ones of Bristol Bay's race. 4) Some 52 and few 63 aged sockeye salmon of Bristol Bay's race which appear in the high sea area near the coast of Asia were bred in 1956 and 1955 respectively. Abundance of appearance of the Bristol Bay's race of sockeye salmon in this sea area, therefore, differs by year in relation to abundance of its fry production of each year.