房総海域におけるマイワシの生活に関する研究-I : 未成魚および成魚の集合様式とI年魚の成熟

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The waters of the Boso Peninsula and Tokyo Bay are one of the most important fishing grounds for the Japanese sardine, Sardinops melanosticta. The present study aims to determine the developmental periods and yearly life cycle of the Japanese sardine population, especially the Pacific fraction, by referring to the previous works. The author examined the mode of aggregation of the immature and adult sardine, and of the maturation of I-aged fish taken from the area during 1967 to 1971. The results are summarized as follows. 1) The immature sardines appear in places shallower thar. 20 meters depth during summer to autumn. The adults appear off shore at 50-100 meters depth during winter to spring (Fig. 4-9). During northward migration the immature sardines increase in their density during life. An examination of the indices of stock size shows fluctuation in the year class. The classes in 1968 and 1971 dominated over the others during the five years under discussion (Table 6). 2) The Pacific fraction of fish. the Japanese sardine. shows a north-south migration in the waters of the Tokai-Tohoku area, Central Japan. The young fish first appears off the entrance of Tokyo Bay and Boso Peninsula in March through June. The immature mostly appear along shore of the Boso Peninsula during early July through November, and are caught chiefly by two-boat purse seiners. After a while, they gradually migrate northward, to as far as off Joban or Sendai Bay in September through November (Fig. 4. 14). During southward migration, the density of the fish decreases and the distribution becomes restricted to off Boso Peninsula in late November through January (Fig. 5). The adult sardines appear off Boso Peninsula and the entrance of Tokyo Bay during late January through May or June (Fig. 6-9). 3) The immature stock comprises two spawning season groups of, large-sized immatures which have spawned in October through December in the latest year and the small-sized ones in January through April (Fig. 10). The former are found off the Boso Peninsula and in the Kashima-nada, while the latter apparently shows a north-south migration from the Boso Peninsula to Joban or Sendai Bay as mentioned already (Fig. 14). 4) The maturation of I-aged fish was distinctly observed in the spawning season during the last four years, and the eggs appeared in the area, corresponding to the shift of the distribution area of the fish (Figs. 3,8,10,12,13). This fact indicates that I-aged fish of the Japanese sardine is the main producer of the eggs found in the waters around and off the Boso Peninsula.
日本生態学会の論文
1973-06-20

房総海域におけるマイワシの生活に関する研究-I : 未成魚および成魚の集合様式とI年魚の成熟

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