Perhaps, the most widespread method of industrial fishery is trawling. During the autumn-winter period it is possible to meet sea expeditions aimed at catching marine inhabitants. Fishing vessels with trawls of various types and designs perform their work to provide different countries and continents with sea production.
First, trawls were used to catch just cod, flounder and navaga at the bottom near the coast. Nowadays, due to the technical progress and innovative development, works on depth up to 2 000m are available, that has essentially enriched the assortment of extraction: now pollack, herring, zimonematosis and whiptail can get into nets.
Trawls are set on trawlers, the most widespread type of fishing vessels. They can be differently equipped, however principals of catching are identical. Vessels are equipped by convenient mechanized lines for rise, cutting, washing, processing, sometimes even preservation of fish, which allows staying in the sea longer. Besides, usually there are freezers on board to keep products fresh.
Many vessels are equipped by echo-sounders, devices controlling parameters of a trawl, allowing to direct it at places of fish concentration.
Types of trawls.
1. Ground. Nets are used for catching inhabitants of sea bottom and sea surface.
It consists of several parts: a trawling cable, shields, cargoes, boards, a hotline and a footrope – the top and bottom network, "wings". By means of special boards a trawl reveals, the top part hangs above the bottom, forms a square, preventing from the loss of the caught fish and giving chances to grasp the shoals going above a surface of sea bottom. The bottom selections are equipped by special adaptations – ground ropes, which allow avoiding touching for stones, rocks. Sideways of a trawl are equipped by "wings" which can also effectively catch fish. While moving the fish is displaced to the distant part of a net. Cells of a net become less, which does not allow the fish to leave.
2. Variable depth. It is used for catching shoals on various depths of water thickness.
It consists of several parts: a trawling cable, shields, cargoes, boards, a hotline and a footrope – the top and bottom network, "wings", but unlike a ground trawl, the top and bottom parts of a net are of the same size. While moving a vessel pulls long tug steel ropes going from boards to a vessel, a trawl reveals, moves, and catching of fish begins.
It is established on large-capacity fishing boats, having onboard system of fish processing.
All trawls are produced from modern, high-strength, facilitated materials, allowing to work longer and more effectively without returning to a coast. This method provides catching with the least expenses of power resources: the equipment and navigation allow to be guided on seat and to find large concentrations of fish, and the system control devices provide maximal catching.