高速表層用稚魚網の試作と曳網試験結果

1) 調査船の舷側を3~ 4ノットで，船橋より常時監視しながら曳網できる，表層用稚魚網(Fig. 1, 5)を試作した。
2) 網を舷側から離し，網が浮きあがらないようにするため，オッターボード，デプレッサー，フロートをとりつけたステンレススチール製の網枠(Fig. 2)を作り，これにナイロン製のもじ網の細長い網(Fig. 3)を取り付けた。
3) 曳網試験を行った結果(Fig. 4, Table. 1) 船首波の影響をほとんどうけずに3~4 ノットで曳網できた。4ノット20分間曳による採集物にはほとんど損傷は見られない。

1) A New type of a surface larva net (Fig.1) was devised and constructed, that could be towed at a rather high speed (3-4 knots) in pararell line with the run of a ship and could also be kept within observable range throughout the operation from the bridge of the of the ship.
2) A stainless steel frame (Fig.2) keeping the mouth of the net open was designed and was equipped with a pair of otter boards, a depresser and a float, in order to keep the net in operation just beneath a water surface without any influence of the bow wave of ship. A net (Fig.3) was made of minnow net of nylon webbing and was installed to the frame.
3) Test operations of the net at seas (Fig. 4, 5, Table. 1) revealed that it could work as predicted, at least within towing speeds of 3 to 4 knots and that fish larvae collected by towing at a speed of 4 knots for 20 minutes showed significantly reduced injury when the codend with a closed end PVC adaptor (Fig. 3-b).