1.Sleeveless single bag trawl
It is a small trawling net. The net mouth generally has a fixed bracket device to keep the mesh opening open, and both the marine and inland waters are used. Sleeveless multi-bag trawling, generally with more than 2 nets. The number of nets depends mainly on the ecological habits of the fishing objects and the tonnage of the fishing vessels. The horizontal and vertical opening of the mesh opening is ensured by means of two ship trawl spacing and vertical struts.
2.Sleeve and sleeveless trawl
It is generally used in the bottom waters, and the middle trawl is mainly used in the middle waters. The difference between it and the bottom trawl is mainly that the general meshless sleeve or the net sleeve is shorter, so that the resistance of the net can be reduced and the drag speed can be increased; the mesh mouth is slightly square or rectangular; the net has a sinker underneath, some A settling device such as a heavy hammer is also installed to enlarge the vertical opening dimension of the mesh opening and to maintain the position of the net in the water layer.
The requirements for trawling on the fishery are: flat bottoms and no obstacles, wide waters, clustered fish, wind and waves are not too big. Middle trawling operations are not limited by water depth and bottom shape. The world's important trawling fisheries are Europe's North Sea, Mediterranean Coast, West African Coast, Arabian Sea, Bay of Bengal, Australia and New Zealand, Okhotsk Sea, Bering Sea, Newfoundland Coast, Gulf of Mexico and Coast of Guyana, Argentina's Batago Niagara and other places. China's coastal areas are also perennial fishing grounds for bottom trawling.