外房に於けるマダコOctopus(Octopus)vul galis Lamarck資源の性状について
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The common octopus, Octopus (Octopus) vulgaris LAMARCK, an important commercial species in Japan, are captured by means of the octopus pot, the hand line and the spear along the east coast of Boso Peninsula, Chiba Pref. (Fig. 1 and Table 1). The writer has made a biological study of the stock of this animal, using the statistic data of the octopus fisheries and based upon the number of specimens taken in Uchiura Bay near Kominato. The results obtained are summarized as follows; (1) It is believed that the octopus stock may be composed of two groups, one inhabiting the coast of Boso Peninsula throughout the year, the other migrating from the north to this district in winter (Figs. 2-5). (2) The maturation phase of the octopus is shown by the gonad index (R) as given in the following formula; R=G. W.×102/[B. W.-(G. W.+F. W.)], where G. W. denotes the gonad weight, F. W. the total weight of digestive organ contents, and B. W. denoting body weight. The relation between gonad index and maturity scale of the female octopus is shown in Table 2. (3) The breeding season is from March to November, and the biological minimum size is about 40cm in the male, 40-50cm in the female (Fig. 6). (4) The monthly increase in the rate of body weight deduced from the body composition (Fig. 7 and Table 3) and the length-weight relationship (Fig. 7 and Table 3) is 0.100 during from March to August, 0.180 from June to December. (5) It may be a reasonable assumption that the immigrant winter group breed during the first breeding season following the migration and that the newly hatched population will increase the available fishing stock from April to July of the following year. (6) Diminishing rate of the octopus stock is estimated by Dr. Tauti's method (1956) as 1-2% per day, 5-8% five days, 8-9% ten days and 13% per month (Table 4). Moreover, the diminishing rate per month is obtained by another Dr. Tauti's method ('53) as being 11%. (7) Judging from the diminishing rate caused by fishing, it may be said that the catch efficiency of the octopus pot is greater than that of the hand line.
- 社団法人 日本水産学会の論文