New autonomous multiple codend opening/closing control system for a midwater frame trawl

A new autonomous multiple codend opening/closing system was constructed to be attached to a midwater trawl net, and the layer discrimination ability of this new system attached to the Matsuda–Oozeki–Hu Trawl (MOHT, mouth area 5 m2) was demonstrated through comparison with the Multiple layer Opening/Closing MOHT (MOC–MOHT), which was equipped with a mouth opening/closing net control system. The new multiple codend opening/closing system was 1.28 m high and 0.75 m wide and has five pyramid-shaped codend nets, with an autonomous control mechanism identical to the MOC–MOHT. Field comparison between the new system and MOC–MOHT demonstrated the accurate layer discrimination ability of the new system and the new codend opening/closing system sufficiently allowed for avoidance of contamination of specimens before the codend frame, after improvement of the main net shape with the cylindrical part before the codend frame. The new autonomous codend opening/closing system attached to MOHT (COC–MOHT) is a reliable multi-layer sampling gear, and the new system itself has the potential of transforming a traditional midwater trawl to an effective multi-layer sampling system, by adding the modification of the net shape before the codend.