Open-water purse seine fishing is widely recognized as an efficient fishing method. There is no contact with the seabed and small amounts of bycatch (incidental capture of unwanted species) can occur. A purse seine can also be used to catch fish that gather around a fish-attracting device. Seine fishing is a fishing method in which a purse seine called a seine is hung vertically on the surface of the water, the lower end is held down by a weight, and the upper end is supported by a float. The seine can be deployed from the shore as a beach seine or from a boat. Boats that use dragnets are called seines. Mainly he deploys two types of dragnets from the dragnet vessel. A dragnet differs from a gillnet in that the sign surrounds the fish, whereas the gillnet catches the fish directly. He has been used extensively in the past, including by Stone Age societies. For example, the Maori used large canoes to deploy dragnets that could exceed a kilometre in length. As swimmers, they used cedar sticks that moved in a way that helped startle fish and keep them together. They appear in Egyptian tomb paintings dating back to 3000 BC. In ancient Roman literature, the poet Ovid makes many references to dragnets, including the use of cork floats and lead weights. There is a common type of dragnet called a purse seine because of the series of rings on the bottom. A line (called a Perth line) passes through all the rings and when pulled, the rings move closer together and prevent fish from "ping" or swimming away from the net. The process is similar to traditional style purses with a drawstring closure. A purse seine is a favourite technique for catching fish species that are huddled or swarming near the surface. Sardines, mackerel, anchovies, herring, and certain types of tuna (shallow water). Salmon swim in rivers and streams just before spawning (aggregation). A ship equipped with a purse seine is called a purse seine. Bycatch with other species and catching schooling in parallel with a collection system dramatically increase bycatch rates. The use of purse seine is regulated in many countries. For example, in Sri Lanka, the use of this type of net is illegal within 7 km (3.8 nautical miles; 4.3 miles) of the coast. However, it can be used in deep water if formal approval is obtained. Purse seine fisheries can have a negative impact on fish stocks as they can cause a bycatch of non-target species and put undue pressure on fish stocks. A power block is a mechanized reel used on some seine vessels to pull nets. The Puretic Power Block line was introduced in the 1950s and was a key factor in the mechanization of purse seine fishing. This type of seine is useful for schooling near-surface fish such as sardines, mackerel, anchovies, herring, and certain species of tuna and salmon. Purse seines can carry a bycatch of non-target species and can put undue pressure on fish stocks. A purse seine consists of a long wall of net surrounded by a lead line that is equal to or longer than the swimming line.