カムチャッカ南東海域におけるシロザケの遊泳行動について

概要

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In order to investigate differences in the swimming behaviour of salmon between the early morning and night, observations were carried out on board the Arisomaru of the Fisheries Agency, Ministry of Agriculture, Japanese Government, in the southeastern area off Kamchatka Peninsula from June 10 to July 26, 1968.Two sets of surface gillnet were set at right angles to each other, following a southeastern direction parallel to Kamchatka Peninsula as shown in Figs. 1, 2. The time duration of the set net was about two hours, one net was set approximately at midnight (night net), and the other one hour after sunrise (morning net) at the same place as shown in Figs. 1, 2. The results of the observations are summarized as follows: 1) The chum salmons caught proved to be mainly 4 years old, exclusively adults, belonging to the west coast population of Kamchatka Peninsula. 2) Chum salmons caught by the night net were almost even with regard to directions. In the case of morning net the catches increased both in southeastern and northeastern directions, coinciding with the migrating direction of this species. 3) As for the difference between the night catch and the morning one, no special biological differences were observed in age composition, sex ratio, gonad weight and volume of stomach contents, etc. of this fish.