微離底曳網の実用化に関する研究

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書誌事項

タイトル別名
  • ビ リ ソコビキアミ ノ ジツヨウカ ニ カンスル ケンキュウ
  • Research on the practicality of the Off bottom Trawl Net
  • ビリテイ ヒキアミ ノ ジツヨウカ ニ カンスル ケンキュウ

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抄録

The off bottom trawl net commonly called Sea slater Net or chain net is a newly deviced fishing net supplied with a fishing line to the lower side of which are attached a series of bothbouys and hanging chains; when this is put under operation this fishing line is to be drawn, detouched more or less off the sea bottom.The possibility of its practicality has been proved by the repeated towing tests carried outon board the training ship.Basing on the assessment of the results obtained from (1) the 4 times drawing testsperformed by the 2 training ship on the East China Sea in 1982 (2) the 25 times fishering testscarried out by the trawler No.37 DAIKICHI MARU on the Bering Sea (3) the model testscarried out in the water tank the following concluusions were fixed concering its practicality.(1) Fishing Capacity :The value of the Catch Per Unit Effort of the chain net was equivalent to 47~82% of that of the regular net. Even put under a statical assessment, in the fish composition of the caughtfish an obvious distinction was noted between the chain net and the regular net; theusefulness of the chain net as a Fish species Selecting apparatus was ascertained. The amount of dergs and drains drawn into the net was noted to be quite negligible.(2) Gearing Capacity :In the both nets, almost no difference was noted between the height of net mouth.Concering the distance between the wing tips, that of the chain net was somewhat lager thanthat of regular net. The net resistance of the chain net was 15~30% less than that ofthe regular net.In the case when fishing was effective, the off bottom height of the chain net was 20~40cm in the Bering Sea, and it was 10~15cm in the East China Sea. The proper shape of thechain which was to be fixed in accordance with its resistance against the flowing water, was sought out theoritically; the diameter of the most proper chain was assessed to be 16mm.The slower was the towing speed, the longer the vertical past of the submerged hangingchain, which prevented fish school from running away : basing on the above mentioned factthe most proper to wing speed of the chain net was fixed to be 3 knots.

底曳網の沈子方のフィッシングラインに浮子と垂下チェーンを数多く装着し,そのラインを海底から微少高さ離底させて曳網する微離底曳網(チェーン網)については,これまで本学練習船により数多くの曳網実験が行なわれ,実用化が可能であることが証明されている。本報は,昭和57年,ベーリング海で行なわれた北転船,第37大吉丸の25回の漁獲試験と東支那海で行なった2隻の本学練習船の4回の曳網実験及び水槽で行なった模型実験の夫々の資料を併せて検討した結果,下記のような結論を得た。1) 漁獲性能 : チェーン網のC・P・U・Eの値は通常網の47~82%に当る。両網の漁獲物の魚種組成は統計学的にみても有意差が認められ,チェーン網の選択漁法の漁具としての有効性を認めることが出来るようである。2) 漁具性能 : 網口高さは両網ともほとんど差はない。袖先間隔はチェーン網が若干広い。チェーン網の抵抗は通常網より15~30%少ない。有漁獲の場合の離底の高さは,ベーリング海では20~45cmである。曳網中におけるチェーンの吹かれの形状を理論的に求めた結果,適正のチェーン径は16mm(16φ)となる。またチェーンの吹かれを考慮すると,適正の曳網速力は3.5ノット以下となる。

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