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「早岐瀬戸」締め切りが周辺真珠漁場に与える影響に関する研究-2 : 漁場の流動状況と夏期の酸素量低下

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タイトル: 「早岐瀬戸」締め切りが周辺真珠漁場に与える影響に関する研究-2 : 漁場の流動状況と夏期の酸素量低下
その他のタイトル: Studies of the Oceanographic Characteristics of Haiki Channel and the Adjacent Waters, and of Effets of Closing of the Channel on Pearl Farms―II Movement of Sea Water and Amount of Dissolved Oxygen in the Farm
著者: 飯塚, 昭二 / 入江, 春彦
著者(別表記) : Iizuka, Syoji / Irie, Haruhiko
発行日: 1967年 3月
出版者: 長崎大学水産学部
引用: 長崎大学水産学部研究報告, v.22, pp.1-14; 1967
抄録: With a presumption that the Channel be closed at the tentative position shown in Fig. 1, futurity of the pearl farm concerned in the mouth region of Haiki Channel on the side of Sasebo Bay is estimated. Surveys were carried out in the Daito Farm attached to T. Pearl Farm Co. Present paper deals only with several problems on the movement of sea water and the depression of dissolved oxygen in the hottest season. From the results obtained, it was found that the characteristics of the farm concerned are as follows. The tidal velocities at spring tide were 8 to 10 cm/sec in average, attaining up to about 25 cm/sec in max.; there was observed a tendency of dissolved oxygen to decrease in the summer but the phenomenon was of small-scale; it was restricted only in the bottom waters and it occurred intermittently for three or four days, the interval agreeing to the periodicity of neap tide, especially in the time of young moon; and dissolved oxygen was not depressed down below 1 cc/L. Those phenomena were not observed in the other depths except in the bottom waters. The amount of oxygen both in surface and middle waters was abundant and did not decrease below 3 cc/L even in the summer season. Therefore, it does not happen under the present circumstances that the cultured shells suffer damage by low oxygen content. However, those features will be changed by closing of the Channel. First of all, on general aspects, velocity in farm will decrease below 1/2 of the present condition, assuming that the velocity after closing will become same as in Sasebo Bay. Such estimation leads to the results that average velocity under the same condition described above will turn into 4-5cm/sec and average velocity throughout the period from spring tide to neap tide will further decrease down to about 3cm/sec. Experiments in aquarium revealed that the current velocity of those values greatly affects normal activity of the shells. Moreover, the decline movement of sea water may secondarily result in such serious trouble that low oxygen water, which is being restricted only in the bottom water under the present condition, will develope and cause damage to the shells hanging in the lower limit of middle water. As the partial conclusion of this paper, the closing of the Channel, being accompanied with lowering of the movement of water, may not ameliorate the futurity of the farm concerned. / 早岐瀬戸締め切り(計画案)にともなう,周辺漁場の価値変化を予測した.対象となった漁場は佐世保湾側出入口にあるT養殖所大塔漁場で,本報では,海水流動と夏期におこる低酸素化の問題について論議した. まず,現況調査から,漁場の平均流速は大潮時で8~10cm/sであることを明かにし,なお時間によっては25cm/s(時期によっては35cm/sになることも推定された)出ることも示した.酸素量については,夏期海底水で小潮時に低酸素化の傾向があるが,(特に上弦の小潮で顕著であった),1cc/Lを下まわることはなかったし,貝かごが垂下されている中層以浅では,海底水で低酸素化する場合にも3cc/Lを下まわることは少なかった. しかし,このような現況は,締め切りによって変化することが予想された.すなわち,流速については現況の1/2以下に低下し,平均流速は大潮時で4~5cm/s,また年間平均流速では3cm/s程度になると推算した.これらの値はアコヤガイの生理活動を著しく阻害する.また,酸素量については,流速の低下にともない,海底水にみられた低酸素化傾向が上昇する可能性も考えられたし,他方,瀬戸内部に群生する海藻群落による酸素供給効果や,観潮橋下のかく乱作用による海水更新効果も阻害される.したがって,締め切りは漁場の将来を決して良い方向には向わせないであろう.
URI: http://hdl.handle.net/10069/31404
ISSN: 05471427
資料タイプ: Departmental Bulletin Paper
原稿種類: publisher

引用URI : http://hdl.handle.net/10069/31404



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