イセエビの漁獲の時間的変化にみられる双峯性について

Abstract

Basing upon the results obtained from 6 catch experiments carried out by using fisherman's lobster net, a kind of gill-net, at Kominato Marine Biological Laboratory of Tokyo University of Fisheries in July 1952, May and July 1953, July 1954, and September 1961 (Table 1), the followings may be mentioned. The Japanese spiny lobster, Panulirus japonicus (v. Siebold) is a nocturnal forager, as is the case with Macrobrachium nipponese (De Haan)3-5), Palaemon (Palaemon) paucidens De Hann8), Penaeus japonicus Bate9-12), Homarus americanus Milne-Edwards2), and Cambaroides japonicus (De Haan)8). A lot of the lobster in each experiment was caught during nighttime from 18 to 6, but only few ones were secured during daytime from 6 to 18: (Table 2). Bimodality of the nocturnal activity of the lobster is found to exist. The catch of the lobster in question shows two modes as given in the Figs. 2 and 3. Those are seen during the period both from 18 to 20 and from 2 to 4 (Table 2 and Figs. 2 and 3). Of these two modes, the first one is somewhat larger than the other. It may be said that the daily rhythmic activity of the lobster belongs to the crepscular type. Finally the followings should be noted herewith. As seen in the Table 2, the catch made under bright moonlight did not decrease as compared with that carried out under new moon. Fishermen, although in Japan, generally do not go out to the sea to catch the lobster during the period of full moon.