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a type of fishing gear consisting principally of netting. The use of nets is the basis of commercial fishing. In terms of the method of catching the fish, fishnets are divided into three basic types: gill, pound, and pass.
Gill nets are used for catching sparse accumulations over a large expanse of water. They can be used in any area of the body of water regardless of the condition of the bottom and the strength of the current. Individual nets, measuring 10–50 long, are joined together into sets, the length of which can reach several kilometers. Anchors and buoys are fastened to the ends of the sets. The nets are placed at depths to 200 m; their width ranges from 0.5 (to catch crab) to 10–15 m (to catch herring). In shallow waters the nets are held stationary on poles. River drift nets are floated downstream behind boats to which they are attached. Sea drift nets are fastened to a common leader cable and are carried along with the vessel. To increase the catch, two- and three-series gill nets are sometimes used.
Pound, or trap, nets are used for catching fish migrating along definite routes off seacoasts and in river mouths. Such fish migrations occur at certain times of the year owing to natural processes in the life cycle, for example, spawning. Typical is a trap net consisting of one or two chambers for collecting and holding the catch and an inlet device that allows the fish to enter the trap easily but obstructs its escape. There is also a guiding wing that forces the fish toward the trap. The wing is a long rectangular net that completely or partially occupies the full depth of the water, from the floor to the surface. In shallow water the nets are usually attached to pilings, and in deep water to a soft rope frame supported by a system of buoys and anchors. The fish are removed by hand or with a fish pump. Other types of pound nets include hoop nets, which are significantly smaller than trap nets.
The pass nets include drag seines, circular seines with pockets, Danish seines, trawls, and townets. Drag seines occupy the full depth of the water. Circular seines occupy a layer of water close to the surface; to capture the fish, the net is closed off from below. A particular feature of Danish seines is that they catch fish only in water close to the bottom, where benthic and bathypelagic fish dwell. Danish seines involve the use of traction guide ropes, which during the pulling in of the seine drive the fish along the path the net is moving. Townets are often used together with artificial light sources and include conical nets for catching sprat and rectangular nets for catching sardines, sauries, and other fishes.
Despite the wide use of fishnets for catching large numbers of fish, this type of fishing gear has significiant shortcomings. The nets are quite large, and their use is labor-intensive and requires high-powered vessels.
REFERENCESSee references under FISHING GEAR.
A. L. FRIDMAN