trawls

The Oxford Companion to Ships and the Sea | 2006 | 700+ words | Copyright

trawls are large nets dragged along the bottom by commercial fishing boats. The mouth of the net is kept open by trawl doors, which not only help to weight the net down, but act like hydroplanes to keep the mouth of the net open. The bottom rope is weighted and has rollers to lift it over seabed obstructions. The head rope is lined with floats. Mesh sizes have to comply with a legal minimum so that undersized fish are allowed to escape. The cod-end is lined with fine mesh to reduce damage to the catch and is tied off with a throttling rope, which is released when the trawl is retrieved. Scientists in research ships who are studying biological oceanography also use different types of trawl, which are smaller, designed so the volumes of water filtered are accurately known, and fitted with electronic sensors. See also fisheries.

M. V. Angel

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