Characteristics
OverviewA midwater otter trawl is a cone-shaped net which is towed in mid-water. It consists of a cone-shaped body, normally made of four panels, ending in a codend and the net has lateral wings extending forward from the opening. The horizontal opening is maintained by otter boards. Floats and/or sailkites on the headline and weights on the groundline provide for the vertical opening. Large modern midwater trawls are rigged in such a way that the weights in front of and along the groundline provide for the vertical opening of the trawl. The cable transmitting acoustic signal form the net sonde might also provide a lifting force that maximize the vertical trawl opening. To reduce the resistance of the gear and achieve a large opening, the front part of the trawls are usually made from very large rhombic or hexagonal meshes. The use of nearly parallel ropes instead of meshes in the front part is also a common design. The largest mesh sizes used so far are 128 m and, on modern large midwater trawls, approximately three quarters of the length of the trawl is made with mesh sizes above 400 mm.