Bottom gill net

              Nylon monofilament and nylon multifilament are the main materials for the netting of most bottom gill nets.  The specifications such as the mesh-size, the length and height of net, and the hanging ratio, vary for different species of marine animals.  In the case of bottom gill net for blue swimming crab which is most widely operated, the mesh-size is about 10-12 cm, height of net is about 120 cm and the hanging ratio is around 0.5.  The bottom gill net for whiting is comparatively smaller than other bottom gill nets; its mesh-size is about 2.5-3.0 cm, height of net is 65-120 cm, and the hanging ratio ranges from 0.52 to 0.68.  In contrast, the bottom gill net for giant queenfish, scad and trevally, has large dimensions; the mesh-size is 9.0-9.5 cm, and height is about 8 m, so that sometimes when it is operated in shallow waters it intercepts anything swimming between the bottom and the surface of the sea.  Bottom gill nets are operated in shallow coastal waters where the depth ranges between 3 and 40 meters.