Gillnetting is a method of fishing that uses gillnets: vertical webs of netting that hang from a fishing line with evenly spaced floats that hold the line to the surface of the water. The floats are sometimes called "corks," and the line with the corks is commonly referred to as "cork fishing line." The fishing line along the bottom of the panels is usually weighted. Traditionally, this fishing line was weighted with lead and may be referred to as "lead line." The gill net is usually set in a straight line. Gillnets can be characterized by the size of the mesh, as well as the color and type of thread they are made from. Fish can be caught with gill nets in three ways:
Cuneiform - held in place by a mesh around the body.
Gills - held in place by the mesh slipping behind the lid.
Tangled - held in place by teeth, spines, maxillary bones, or other protrusions, with the body not passing through the mesh.
More often than not, fish have gills. The fish swims into the net and only goes part of the way through the net. When it tries to free itself, the string slips behind the gill cover and prevents escape.
Gillnets are so effective that their use is closely monitored and regulated by the fisheries management and enforcement agencies. Mesh size, twine strength, and net length and depth are strictly regulated to reduce bycatch of non-target species. Gillnets have a high degree of size selectivity. In particular, most salmon fisheries have extremely low catch rates of non-target species.
A fishing boat adapted to catch fish with a gill net is called a gillnetter. A gill net that deploys its gill net from the bow is a bow trap, while one that deploys its gill net from the stern is a stern trap. Gillnets differ from seines in that the latter uses a tighter weave to catch fish in an enclosed space, instead of directly catching fish as in a gillnet.
Double-walled gill net - consists of two webs planted on combined sets separately - upper and lower sets or planted on the combined upper set, and the lower edges of the net are attached to separate sets. It is used to catch fish of different species. The mesh of each wall should be according to the size of the fish to be caught.