Drift net
Encyclopedia
Drift netting is a fishing
technique where nets
, called drift nets, are allowed to float freely at the surface of a sea or lake. Usually a drift net is a gill net with floats attached to a rope along the top of the net, and weights attached to another rope along the foot of the net to keep the net vertical in the water. Drift nets are placed by ships and are left free-floating until retrieved. These nets usually target schools of pelagic fish
. Drift nets are a type of gill net because of the tendency for the fishes' gills to get caught in the net.
Traditionally drift nets were made of organic materials, such as hemp
, which were biodegradable
. Prior to 1950s, nets tended to have a larger mesh
size. The larger mesh only caught the larger fish, allowing the smaller, younger ones to slip through. When drift net fishing became large scale during 1950s, nets were changed to synthetic
materials with smaller mesh size. Synthetic nets last longer, are odorless, and are nearly invisible in the water, but did not biodegrade.
Drift net fishing became a desirable fishing practice because it is extremely cost effective. Nets can be placed by low-powered vessels making it very fuel efficient. Drift nets are also highly effective at bringing in large amounts of fish in one catch.
Prior to 1960s net size was not limited, and commercially produced nets were commonly as long as 50 km (~31 miles). In 1987 the U.S. enacted the Driftnet Impact, Monitoring, Assessment and Control Act limiting the length of nets used in American waters to 1.5 nautical mile
s (~1.7 miles). In 1992 the United Nations General Assembly
(UNGA) banned the practice of drift net fishing.
. In 1994 United Nations Food and Agriculture Organization
(UNFAO) estimated global by-catch rates to be as high as 27 million tons of fish discarded by fisheries each year. Many individuals of non-target species perish as by-catch in the cast of each drift net. As a result, many of these species are now endangered. Species caught as by-catch include shark
s, dolphin
s, whale
s, turtle
s, sea birds
, and other marine mammal
s. Since nets are placed and may not be retrieved for days, air-breathing mammals that become tangled in the nets drown if they are unable to free themselves.
In 1990s drift net fisheries were responsible for 30,000 tons of sharks and skates in global by-catch annually. While filming National Geographic's Incidental Kill in the California Channel Islands
where swordfish
and various sharks swim north, Howard Hall and his diving crew discovered many drift net boats had placed nets that night. The nets were one mile long each and nearly 100 feet high placed to target swordfish and thresher sharks. Hall and his crew swam half the length of one net and in that length discovered 32 dead blue shark
s in the net as well as 2 hammer head sharks, a sea lion
, and a manta ray
all of which were thrown back into the ocean when the net was hauled in.
Although long line 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.
Catch that is non-targeted or unmarketable is thrown back to the ocean as dead material or with injuries that may result in death. Dead material thrown back into the ocean, if not eaten, decomposes
. In order for the carcasses to decompose, bacteria use oxygen
to break down the organic matter
. Large amounts of dead matter decomposing in the ocean causes the surrounding levels of dissolved oxygen
to decrease.
s. Synthetic nets are resistant to rot or breakdown, therefore ghost nets fish indefinitely in the oceans. Marine animals are easily tangled in ghost nets. The float line on the net allows it to be pushed in the current which causes ecological
damage to plant life and substrate
habitats as the nets drag the sea floor.
, set by the Law of the Sea
. Outside these boundaries lie international waters
, or the high seas. While fishing in international waters vessels must comply with regulations of the country in whose flag they fly, but there are no enforcers of the high seas. International waters make up 50% of the world's surface, yet are the least protected habitat on Earth.
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. Illegal fishing is 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.
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 definition put in place. A new definition of what accounted as a drift net 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".
Japan
ese 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 North 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 the indiscriminate destruction of marine life, but also for the poaching of 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.
Fishing
Fishing is the activity of trying to catch wild fish. Fish are normally caught in the wild. Techniques for catching fish include hand gathering, spearing, netting, angling and trapping....
technique where nets
Fishing net
A fishing net or fishnet is a net that is used for fishing. Fishing nets are meshes usually formed by knotting a relatively thin thread. Modern nets are usually made of artificial polyamides like nylon, although nets of organic polyamides such as wool or silk thread were common until recently and...
, called drift nets, are allowed to float freely at the surface of a sea or lake. Usually a drift net is a gill net with floats attached to a rope along the top of the net, and weights attached to another rope along the foot of the net to keep the net vertical in the water. Drift nets are placed by ships and are left free-floating until retrieved. These nets usually target schools of pelagic fish
Pelagic fish
Pelagic fish live near the surface or in the water column of coastal, ocean and lake waters, but not on the bottom of the sea or the lake. They can be contrasted with demersal fish, which do live on or near the bottom, and reef fish which are associated with coral reefs.The marine pelagic...
. Drift nets are a type of gill net because of the tendency for the fishes' gills to get caught in the net.
Traditionally drift nets were made of organic materials, such as hemp
Hemp
Hemp is mostly used as a name for low tetrahydrocannabinol strains of the plant Cannabis sativa, of fiber and/or oilseed varieties. In modern times, hemp has been used for industrial purposes including paper, textiles, biodegradable plastics, construction, health food and fuel with modest...
, which were biodegradable
Biodegradation
Biodegradation or biotic degradation or biotic decomposition is the chemical dissolution of materials by bacteria or other biological means...
. Prior to 1950s, nets tended to have a larger mesh
Mesh
Mesh consists of semi-permeable barrier made of connected strands of metal, fiber, or other flexible/ductile material. Mesh is similar to web or net in that it has many attached or woven strands.-Types of mesh:...
size. The larger mesh only caught the larger fish, allowing the smaller, younger ones to slip through. When drift net fishing became large scale during 1950s, nets were changed to synthetic
Synthetic fiber
Synthetic fibers are the result of extensive research by scientists to improve on naturally occurring animal and plant fibers. In general, synthetic fibers are created by forcing, usually through extrusion, fiber forming materials through holes into the air, forming a thread...
materials with smaller mesh size. Synthetic nets last longer, are odorless, and are nearly invisible in the water, but did not biodegrade.
Drift net fishing became a desirable fishing practice because it is extremely cost effective. Nets can be placed by low-powered vessels making it very fuel efficient. Drift nets are also highly effective at bringing in large amounts of fish in one catch.
Prior to 1960s net size was not limited, and commercially produced nets were commonly as long as 50 km (~31 miles). In 1987 the U.S. enacted the Driftnet Impact, Monitoring, Assessment and Control Act limiting the length of nets used in American waters to 1.5 nautical mile
Nautical mile
The nautical mile is a unit of length that is about one minute of arc of latitude along any meridian, but is approximately one minute of arc of longitude only at the equator...
s (~1.7 miles). In 1992 the United Nations General Assembly
United Nations General Assembly
For two articles dealing with membership in the General Assembly, see:* General Assembly members* General Assembly observersThe United Nations General Assembly is one of the five principal organs of the United Nations and the only one in which all member nations have equal representation...
(UNGA) banned the practice of drift net fishing.
By-catch
Any fish that crosses the path of a drift net in the ocean may be tangled or caught in the net. Any non-target individual caught in the net is called by-catchBycatch
The term “bycatch” is usually used for fish caught unintentionally in a fishery while intending to catch other fish. It may however also indicate untargeted catch in other forms of animal harvesting or collecting...
. In 1994 United Nations Food and Agriculture Organization
Food and Agriculture Organization
The Food and Agriculture Organization of the United Nations is a specialised agency of the United Nations that leads international efforts to defeat hunger. Serving both developed and developing countries, FAO acts as a neutral forum where all nations meet as equals to negotiate agreements and...
(UNFAO) estimated global by-catch rates to be as high as 27 million tons of fish discarded by fisheries each year. Many individuals of non-target species perish as by-catch in the cast of each drift net. As a result, many of these species are now endangered. Species caught as by-catch include shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....
s, dolphin
Dolphin
Dolphins are marine mammals that are closely related to whales and porpoises. There are almost forty species of dolphin in 17 genera. They vary in size from and , up to and . They are found worldwide, mostly in the shallower seas of the continental shelves, and are carnivores, mostly eating...
s, whale
Whale
Whale is the common name for various marine mammals of the order Cetacea. The term whale sometimes refers to all cetaceans, but more often it excludes dolphins and porpoises, which belong to suborder Odontoceti . This suborder also includes the sperm whale, killer whale, pilot whale, and beluga...
s, turtle
Turtle
Turtles are reptiles of the order Testudines , characterised by a special bony or cartilaginous shell developed from their ribs that acts as a shield...
s, sea birds
Seabird
Seabirds are birds that have adapted to life within the marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same environmental problems and feeding niches have resulted in similar adaptations...
, and other marine mammal
Marine mammal
Marine mammals, which include seals, whales, dolphins, and walruses, form a diverse group of 128 species that rely on the ocean for their existence. They do not represent a distinct biological grouping, but rather are unified by their reliance on the marine environment for feeding. The level of...
s. Since nets are placed and may not be retrieved for days, air-breathing mammals that become tangled in the nets drown if they are unable to free themselves.
In 1990s drift net fisheries were responsible for 30,000 tons of sharks and skates in global by-catch annually. While filming National Geographic's Incidental Kill in the California Channel Islands
Channel Islands of California
The Channel Islands of California are a chain of eight islands located in the Pacific Ocean off the coast of Southern California along the Santa Barbara Channel in the United States of America...
where swordfish
Swordfish
Swordfish , also known as broadbill in some countries, are large, highly migratory, predatory fish characterized by a long, flat bill. They are a popular sport fish of the billfish category, though elusive. Swordfish are elongated, round-bodied, and lose all teeth and scales by adulthood...
and various sharks swim north, Howard Hall and his diving crew discovered many drift net boats had placed nets that night. The nets were one mile long each and nearly 100 feet high placed to target swordfish and thresher sharks. Hall and his crew swam half the length of one net and in that length discovered 32 dead blue shark
Blue shark
The blue shark is a species of requiem shark, family Carcharhinidae, that inhabits deep waters in the world's temperate and tropical oceans. Preferring cooler waters, blue sharks migrate long distances, for example from New England to South America. Although generally lethargic, they can move very...
s in the net as well as 2 hammer head sharks, a sea lion
Sea Lion
Sea lions are pinnipeds characterized by external ear-flaps, long fore-flippers, the ability to walk on all fours, and short thick hair. Together with the fur seal, they comprise the family Otariidae, or eared seals. There are six extant and one extinct species in five genera...
, and a manta ray
Manta ray
The manta ray is the largest species of the rays. The largest known specimen was more than across, with a weight of about . It ranges throughout waters of the world, typically around coral reefs...
all of which were thrown back into the ocean when the net was hauled in.
Although long line 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
Baltic Sea
The Baltic Sea is a brackish mediterranean sea located in Northern Europe, from 53°N to 66°N latitude and from 20°E to 26°E longitude. It is bounded by the Scandinavian Peninsula, the mainland of Europe, and the Danish islands. It drains into the Kattegat by way of the Øresund, the Great Belt and...
estimate that 90,000 sea birds die annually in drift nets.
Catch that is non-targeted or unmarketable is thrown back to the ocean as dead material or with injuries that may result in death. Dead material thrown back into the ocean, if not eaten, decomposes
Decomposition
Decomposition is the process by which organic material is broken down into simpler forms of matter. The process is essential for recycling the finite matter that occupies physical space in the biome. Bodies of living organisms begin to decompose shortly after death...
. In order for the carcasses to decompose, bacteria use oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
to break down the organic matter
Organic matter
Organic matter is matter that has come from a once-living organism; is capable of decay, or the product of decay; or is composed of organic compounds...
. Large amounts of dead matter decomposing in the ocean causes the surrounding levels of dissolved oxygen
Oxygen saturation
Oxygen saturation or dissolved oxygen is a relative measure of the amount of oxygen that is dissolved or carried in a given medium. It can be measured with a dissolved oxygen probe such as an oxygen sensor or an optode in liquid media, usually water.It has particular significance in medicine and...
to decrease.
Environmental damage
Drift nets lost or abandoned at sea due to storms causing strong currents, accidental loss, or purposeful discard become ghost netGhost net
Ghost nets are fishing nets that have been left or lost in the ocean by fishermen. These nets, often nearly invisible in the dim light, can be left tangled on a rocky reef or drifting in the open sea. They can entangle fish, dolphins, sea turtles, sharks, dugongs, crocodiles, seabirds, crabs, and...
s. Synthetic nets are resistant to rot or breakdown, therefore ghost nets fish indefinitely in the oceans. Marine animals are easily tangled in ghost nets. The float line on the net allows it to be pushed in the current which causes ecological
Ecology
Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...
damage to plant life and substrate
Substrate (marine biology)
Stream substrate is the material that rests at the bottom of a stream. There are several classification guides. One is:*Mud – silt and clay.*Sand – Particles between 0.06 and 2 mm in diameter.*Granule – Between 2 and 4 mm in diameter....
habitats as the nets drag the sea floor.
Illegal fishing
Each country has jurisdiction over the waters within 200 nautical miles of their shores, called the exclusive economic zoneExclusive Economic Zone
Under the law of the sea, an exclusive economic zone is a seazone over which a state has special rights over the exploration and use of marine resources, including production of energy from water and wind. It stretches from the seaward edge of the state's territorial sea out to 200 nautical...
, set by the Law of the Sea
United Nations Convention on the Law of the Sea
The United Nations Convention on the Law of the Sea , also called the Law of the Sea Convention or the Law of the Sea treaty, is the international agreement that resulted from the third United Nations Conference on the Law of the Sea , which took place from 1973 through 1982...
. Outside these boundaries lie international waters
International waters
The terms international waters or trans-boundary waters apply where any of the following types of bodies of water transcend international boundaries: oceans, large marine ecosystems, enclosed or semi-enclosed regional seas and estuaries, rivers, lakes, groundwater systems , and wetlands.Oceans,...
, or the high seas. While fishing in international waters vessels must comply with regulations of the country in whose flag they fly, but there are no enforcers of the high seas. International waters make up 50% of the world's surface, yet are the least protected habitat on Earth.
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. Illegal fishing is 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.
Despite controls, violations of drift net fishing laws are commonplace. The Mediterranean Sea
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
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 definition put in place. A new definition of what accounted as a drift net 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".
Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
ese 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 North Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
to catch tuna
Tuna
Tuna is a salt water fish from the family Scombridae, mostly in the genus Thunnus. Tuna are fast swimmers, and some species are capable of speeds of . Unlike most fish, which have white flesh, the muscle tissue of tuna ranges from pink to dark red. The red coloration derives from myoglobin, an...
and squid
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...
. Japan operated about 900 drift net vessels earning around $300 million a year. Those fishing boats were blamed not only for the indiscriminate destruction of marine life, but also for the poaching of 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
George W. Bush administration
The presidency of George W. Bush began on January 20, 2001, when he was inaugurated as the 43rd President of the United States of America. The oldest son of former president George H. W. Bush, George W...
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.
Other uses
Drift nets also are used in ecological studies in regard to downstream drift of invertebrates. The nets are strung across a stream and allowed to sit over night, collecting samples. These nets are crucial in the understanding of how watersheds function.External links
- "Fishy Business": documentary film about the illegal driftnet fishery in the Mediterranean
- National Geographic's An Incidental Kill