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Drift netting is a fishing technique where Fishing net, called drift nets, hang vertically in the water column without being anchored to the bottom. The nets are kept vertical in the water by Fishing float attached to a rope along the top of the net and weights attached to another rope along the bottom of the net.Caddell, R., "Caught in the net: driftnet fishing restrictions and the european court of justice", "Journal of Environmental Law", 2010 Drift nets generally rely on the entanglement properties of loosely affixed netting. Folds of loose netting, much like a window drapery, snag on a fish's tail and fins and wrap the fish up in loose netting as it struggles to escape. However, the nets can also function as if fish are captured when their gills get stuck in the net. The size of the mesh varies depending on the fish being targeted. These nets usually target schools of pelagic fish.
Traditionally drift nets were made of organic materials, such as hemp, which were biodegradation. Prior to 1950, nets tended to have a larger mesh size.Potter, E.C.E., and Pawson, "Gillnetting (Laboratory Leaflet Number 69)", "Ministry of Agriculture, Fisheries, and Food, Directorate of Fisheries Research", 1991 The larger mesh only caught the larger fish, allowing the smaller, younger ones to slip through. When drift net fishing grew in scale during the 1950s, the industry changed to synthetic fiber materials with smaller mesh size. Synthetic nets last longer, are odourless and may be nearly invisible in the water, and do not biodegrade. Most countries regulate drift net fisheries within their territories. Such fisheries are also often regulated by international agreements.
Drift net fishing became a commercial fishing practice because it is cost effective. Nets can be placed by low-powered vessels making it fuel efficient. Drift nets are also effective at bringing in large amounts of fish in one catch.
Prior to the 1960s net size was not limited, and commercially produced nets were commonly as long as .Animal Welfare Institute, "Driftnet Fishing", 2014 In 1987 the U.S. enacted the Driftnet Impact, Monitoring, Assessment and Control Act limiting the length of nets used in American waters to . In 1989 the United Nations General Assembly (UNGA) placed a moratorium on the practice of drift net fishing.Michaels, P.A., "Cooperative efforts dealing with driftnet fishing" , 2006 In 1992 the UN banned the use of drift nets longer than 2.5 km long in international waters.
In the 1990s, drift net fisheries were responsible for 30,000 tons of sharks and skates in global by-catch annually.Bonfil, R., , "Pacific Fisheries Coalition, Shark Conference Hawaii", 2000 While filming National Geographic's Incidental Kill National Geographic's Incidental Kill in the California Channel Islands where swordfish and various sharks swim north, the divers discovered that many drift net boats had placed nets that night. The nets were one mile long each and nearly high placed to target swordfish and thresher sharks. They swam half the length of one net and in that length discovered 32 dead in the net as well as 2 , a sea lion, and a manta ray all of which were thrown back into the ocean when the net was hauled in.Hall, H. "Web Across the Currents" , 1987
Although longline fishing fisheries are the main contributor to sea bird by-catch, sea birds are also caught in drift nets in significant numbers. Studies conducted on 30 small-scale drift net fisheries in the Baltic Sea estimate that 90,000 sea birds die annually in drift nets.Zydelis, R., "Bycatch in gillnet fisheries - an overlooked threat to waterbird populations" , "Biological Conservation", 2009
Bycatch is thrown back to the ocean either dead or with injuries that may result in death. If not eaten, dead animals decomposition, as bacteria use oxygen to break down the organic matter.Murphy, S., "General information on dissolved oxygen", 2007 Large amounts of dead matter decomposing in the ocean causes the surrounding levels of dissolved oxygen to decrease.
In addition, oceanic microplastics pollution is largely caused by plastic-made fishing gear like drift nets, that are wearing down by use, lost or thrown away.
Declining fish stocks have caused illegal fishing practices to increase. Illegal, unregulated, or unreported fishing catch between 11 and 26 million tons a year which accounts for one quarter of global catch. Marine Stewardship Council Illegal fishing includes taking undersized fish, fishing in closed waters, taking more fish than permitted, or fishing during seasonal closures. Illegal fishing is prominent due to lack of enforcement or punishments.Monterey Bay Aquarium, "Seafood watch" ,
Despite controls, violations of drift net fishing laws are commonplace. The Mediterranean Sea is the most overexploited. With 21 modern states with coastline on the sea, there are many fisheries harvesting one small area. When drift net gear was banned, manufacturers modified the design of the nets so they no longer fell under the banned definition. A new definition was established in 2007 as "any gillnet held on the sea surface or at a certain distance below it by floating devices, drifting with the current, either independently or with the boat to which it may be attached. It may be equipped with devices aiming to stabilize the net or to limit drift".
drift net fishing began to draw public attention in the mid-1980s when Japan and other Asian countries began to send large fleets to the Pacific Ocean to catch tuna and squid. Japan operated about 900 drift net vessels, earning around $300 million a year. Those fishing boats were blamed not only for indiscriminate destruction of marine life, but also for poaching North Pacific salmon, harming the U.S. and Canadian fishing industries, and threatening the jobs of fishermen who did not use such methods. The first Bush administration opposed a U.S. driftnet ban because it would allegedly conflict with a treaty with Japan and Canada regarding salmon fishing in the North Pacific.Spalding, M., www.misr5.com/99414/تفحيط/, 2014
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