海域における養魚場の海水交流に関する研究 (2)　小割の海水交流の一例

The present work deals with the exchange of the sea water of the floating net cultivating yellow tail in the Daio Bay. The direction of tidal current measured by current drags is shown in Fig. 1. The water in the Daio Bay mainly circulated anti-clockwise when the current of its outside was northeast, while the former moved clock- wise when the latter was southwest. But the circulating current was disordered with decrease of the current velocity in the outside. The current velocity in the neighborhood of the floating net was about a half of the outside of the Daio Bay (Figs. 2 and 4). As shown in Table 6, the current within the floating net showed decrease in velocity by the resistance from the net and was about seventy percent of the current of its neighborhood. The direction of current in the net was as same as that of neighborhood during the period of strong current, but they became to differ cach other with decreasing of the current velocity as shown in Table 5. It was considered to be due to the fact that the current was confused by the circular swimming of fish in the net. The circular swimming of fish was observed to be vigorous during four hours after the sunrise and the most vigorous at the time of feeding. The fish did not indicate any stopping in their movement during the night under lighting. The eddy current developed on the surface of sea water when the fish swam vigorously. The volume of exchanged water in one tide calculated from the current velocity in the net is given in Table 7, and it is about two hundred times as large as the volume of the net. The variation of the volume of exchanged water and the amount of dissolved oxygen every one hour are shown in Fig. 6. Consequently, it is considered that the capacity of fish in the floating net must be decided by the smallest volume of exchanged water per hour, because the amount of dissolved oxygen available for fish varies with the volume of exchanged water.

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1. 広島県似島大黄湾にある小割についてその海水の交流を明らかにした。2. 大黄湾の流向は湾外の北東流,南西流にしたがって反時計回りおよび時計回りの環流が主体をなし,湾外の流速がおとろえるとこの環流の傾向はくずれて複雑となる。小割のおかれている湾奥部の流速は湾外の流速の約1/2に低下していた。3. 小割内の流速は小割外の流速の60.3~70.2%に低下し,潮流の速いときは小割内外の流向はほぼ同一であるが,流速がおとろえるにつれてその傾向はくずれてくる。この原因は魚の群行動も一因をなしているものと考えた。4. 小割内の魚の群行動は日の出ごろから約4時間の間はかなり活発であり,最も活発なのは投餌の時である。夜間は20Wの螢光燈を点燈した条件のもとで魚はゆるやかに回遊していて静止することはなかった。群行動の活発な時には小割内に渦流が生じるがその流速は1~3cm/sec程度であった。5. 小割では交流量の時間的変化もはげしいので,1潮時の交流量の時間的変化を求め,単位時間当りの最小交流量を基礎として放養量を検討すべきであると考える。

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bibliographic_information

ja : 内海区水産研究所研究報告
en : Bulletin of Naikai Regional Fisheries Research Laboratory

巻 23, p. 21-43, ページ数 23, 発行日 1966-03

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内海区水産研究所

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Naikai Regional Fisheries Research Laboratory

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item_10002_source_id_9

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収録物識別子

0497-5022

item_10002_source_id_11

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NCID

収録物識別子

AN00176718

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