Drift netting

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Drift netting.

Drift netting is a fishing technique where nets, called drift nets, hang vertically in the water column without being anchored to the bottom. The nets are kept vertical in the water by floats attached to a rope along the top of the net and weights attached to another rope along the bottom of the net. [1] 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 gill nets 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.

Contents

Traditionally drift nets were made of organic materials, such as hemp, which were biodegradable. Prior to 1950, nets tended to have a larger mesh size. [2] 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 materials with smaller mesh size. [1] Synthetic nets last longer, are odourless and may be nearly invisible in the water, and do not biodegrade. [2] 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. [1]

Prior to the 1960s net size was not limited, and commercially produced nets were commonly as long as 50 kilometres (31 mi). [3] 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 miles (1.7 mi; 2.8 km). In 1989 the United Nations General Assembly (UNGA) placed a moratorium on the practice of drift net fishing. [4] In 1992 the UN banned the use of drift nets longer than 2.5 km long in international waters. [5]

Controversy

Bycatch

Any fish that crosses the path of a drift net in the ocean may be tangled or caught in the net. This leads to fish species becoming endangered or even extinct. Non-target individuals caught in the net are called by-catch. 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. [6] Many individuals of non-target species perish as by-catch in the cast of each drift net. As a result, many such species are now endangered. [7] Species caught as by-catch include sharks, dolphins, whales, turtles, sea birds, and other marine mammals. 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 certain areas, exemption from punitive measure due to the unintentional by-catch of marine mammals, as outlined by the Marine Mammal Protection Act, is extended to commercial drift fishermen. [8]

In the 1990s, drift net fisheries were responsible for 30,000 tons of sharks and skates in global by-catch annually. [9] While filming National Geographic's Incidental Kill [10] 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 100 feet (30 m) high placed to target swordfish and thresher sharks. They swam half the length of one net and in that length discovered 32 dead blue sharks in the net as well as 2 hammerhead sharks, a sea lion, and a manta ray all of which were thrown back into the ocean when the net was hauled in. [11]

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. [12]

Bycatch is thrown back to the ocean either dead or with injuries that may result in death. If not eaten, dead animals decompose, as bacteria use oxygen to break down the organic matter. [13] Large amounts of dead matter decomposing in the ocean causes the surrounding levels of dissolved oxygen to decrease.

Environmental damage

Drift nets lost or abandoned at sea due to storms causing strong currents, accidental loss, or purposeful discard become ghost nets. Synthetic nets are resistant to rot or breakdown, therefore ghost nets fish indefinitely in the oceans. Marine animals are easily tangled in ghost nets as are the predators the dead animals attract. 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. [14]

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. [15] [16]

Illegal fishing

Most countries have jurisdiction over the waters within 200 nautical miles of their shores, called the exclusive economic zone, set by the Law of the Sea. [17] 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 on the high seas. International waters make up 50% of the world's surface, yet are its least protected habitat. [18]

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. [19] 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. [20]

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". [1]

Japanese 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 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. [21]

Other uses

Drift nets also are used in ecological studies in studying the downstream drift of invertebrates and Ichthyoplankton. The nets are strung across a stream and allowed to sit overnight, collecting samples. These nets are crucial in the understanding of how watersheds function.[ citation needed ] Quantitative estimates derived from drift nets used in this way in rivers need careful consideration given the clogging of the nets and decay in performance that can occur as a result. [22]

See also

Related Research Articles

<span class="mw-page-title-main">Trawling</span> Method of catching fish

Trawling is an industrial method of fishing that involves pulling a fishing net, that is heavily weighted to keep it on the seafloor, through the water behind one or more boats. The net used for trawling is called a trawl. This principle requires netting bags which are towed through water to catch different species of fishes or sometimes targeted species. Trawls are often called towed gear or dragged gear.

<span class="mw-page-title-main">Longline fishing</span> Commercial fishing technique

Longline fishing, or longlining, is a commercial fishing angling technique that uses a long main line with baited hooks attached at intervals via short branch lines called snoods or gangions. A snood is attached to the main line using a clip or swivel, with the hook at the other end. Longlines are classified mainly by where they are placed in the water column. This can be at the surface or at the bottom. Lines can also be set by means of an anchor, or left to drift. Hundreds or even thousands of baited hooks can hang from a single line. This can lead to many deaths of different marine species. Longliners – fishing vessels rigged for longlining – commonly target swordfish, tuna, halibut, sablefish and many other species.

<span class="mw-page-title-main">Bycatch</span> Fish or other marine species that is caught unintentionally

Bycatch, in the fishing industry, is a fish or other marine species that is caught unintentionally while fishing for specific species or sizes of wildlife. Bycatch is either the wrong species, the wrong sex, or is undersized or juveniles of the target species. The term "bycatch" is also sometimes used for untargeted catch in other forms of animal harvesting or collecting. Non-marine species that are caught but regarded as generally "undesirable" are referred to as rough fish or coarse fish.

<span class="mw-page-title-main">Shark net</span> A submerged barrier that protects swimmers from shark attacks

A shark net is a submerged section of gillnets placed at beaches designed to intercept large marine animals including sharks, with the aim to reduce the likelihood of shark attacks on swimmers. Shark nets used are gillnets which is a wall of netting that hangs in the water and captures the marine animals by entanglement, however only around 10% of catch is the intended target shark species. The nets in Queensland, Australia, are typically 186m long, set at a depth of 6m, have a mesh size of 500mm and are designed to catch sharks longer than 2m in length. The nets in New South Wales, Australia, are typically 150m long, set on the sea floor, extending approximately 6m up the water column, are designed to catch sharks longer than 2m in length. Shark nets do not create an exclusion zone between sharks and humans, and are not to be confused with shark barriers.

<span class="mw-page-title-main">Gillnetting</span> Type of fishing net

Gillnetting is a fishing method that uses gillnets: vertical panels of netting that hang from a line with regularly spaced floaters that hold the line on the surface of the water. The floats are sometimes called "corks" and the line with corks is generally referred to as a "cork line." The line along the bottom of the panels is generally weighted. Traditionally this line has been weighted with lead and may be referred to as "lead line." A gillnet is normally set in a straight line. Gillnets can be characterized by mesh size, as well as colour and type of filament from which they are made. Fish may be caught by gillnets in three ways:

  1. Wedged – held by the mesh around the body.
  2. Gilled – held by mesh slipping behind the opercula.
  3. Tangled – held by teeth, spines, maxillaries, or other protrusions without the body penetrating the mesh.
<span class="mw-page-title-main">Commercial fishing</span> Catching seafood for commercial profit

Commercial fishing is the activity of catching fish and other seafood for commercial profit, mostly from wild fisheries. It provides a large quantity of food to many countries around the world, but those who practice it as an industry must often pursue fish far into the ocean under adverse conditions. Large-scale commercial fishing is called industrial fishing.

<span class="mw-page-title-main">Cetacean bycatch</span> Accidental capture of porpoises, whales and dolphins

Cetacean bycatch is the accidental capture of non-target cetacean species such as dolphins, porpoises, and whales by fisheries. Bycatch can be caused by entanglement in fishing nets and lines, or direct capture by hooks or in trawl nets.

<span class="mw-page-title-main">Turtle excluder device</span> Device for freeing sea turtles from bycatch

A turtle excluder device (TED) is a specialized device that allows a captured sea turtle to escape when caught in a fisherman's net.

<span class="mw-page-title-main">Ghost net</span> Fishing net left or lost in the sea, that endangers marine animals or human divers

Ghost nets are fishing nets that have been abandoned, lost, or otherwise discarded in the ocean, lakes, and rivers. 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 other creatures, including the occasional human diver. Acting as designed, the nets restrict movement, causing starvation, laceration and infection, and suffocation in those that need to return to the surface to breathe. It's estimated that around 48,000 tons of ghost nets are generated each year, and these may linger in the oceans for a considerable time before breaking-up.

<span class="mw-page-title-main">Fish aggregating device</span> Man-made object used to attract ocean-going pelagic fish

A fish aggregatingdevice (FAD) is a man-made object used to attract ocean-going pelagic fish such as marlin, tuna and mahi-mahi. They usually consist of buoys or floats tethered to the ocean floor with concrete blocks. FADs attract fish for numerous reasons that vary by species.

In fishing, incidental catch refers to the portion of the catch that was unintentionally caught but retained. It can be distinguished from discards, which are the unintended catch that is caught and then returned to the sea, and bycatch, which includes all non-targeted species caught alongside the targeted species.

<span class="mw-page-title-main">Grey nurse shark conservation</span> Conservation management of grey nurse sharks

One of the first shark species to be protected was the grey nurse shark. The biology, distribution and conservation of this species are dealt with in the following paragraphs with a main focus on Australia as it was here it first became protected.

<span class="mw-page-title-main">Environmental impact of fishing</span>

The environmental impact of fishing includes issues such as the availability of fish, overfishing, fisheries, and fisheries management; as well as the impact of industrial fishing on other elements of the environment, such as bycatch. These issues are part of marine conservation, and are addressed in fisheries science programs. According to a 2019 FAO report, global production of fish, crustaceans, molluscs and other aquatic animals has continued to grow and reached 172.6 million tonnes in 2017, with an increase of 4.1 percent compared with 2016. There is a growing gap between the supply of fish and demand, due in part to world population growth.

Dolphin-safe labels are used to denote compliance with laws or policies designed to minimize dolphin fatalities during fishing for tuna destined for canning.

This is a glossary of terms used in fisheries, fisheries management and fisheries science.

Destructive fishing practices are fishing practices which easily result in irreversible damage to habitats and the sustainability of the fishery ecosystems. Such damages can be caused by direct physical destruction of the underwater landform and vegetation, overfishing indiscriminate killing/maiming of aquatic life, disruption of vital reproductive cycles, and lingering water pollution.

<span class="mw-page-title-main">Fishing industry in the United States</span>

As with other countries, the 200 nautical miles (370 km) exclusive economic zone (EEZ) off the coast of the United States gives its fishing industry special fishing rights. It covers 11.4 million square kilometres, which is the second largest zone in the world, exceeding the land area of the United States.

<span class="mw-page-title-main">Tangle net</span> Type of nylon fishing net

Similar to a gillnet, the tangle net, or tooth net, is a type of nylon fishing net. Left in the water for no more than two days, and allowing bycatch to be released alive, this net is considered to be less harmful that other nets. The tangle net is used in the Philippines by commercial fishermen, as well as by the scientific community. When spent, these nets can be bundled, and left on the sea floor to collect smaller species. These bundles are known locally as lumen lumen nets.

The following outline is provided as an overview of and topical guide to fisheries:

In the fishery business, a bycatch reduction device is a tool designed to minimize unintended capture of marine animals, to reduce the adverse effects of fishing on the ecosystem.

References

  1. 1 2 3 4 Caddell, R., "Caught in the net: driftnet fishing restrictions and the european court of justice", "Journal of Environmental Law", 2010
  2. 1 2 Potter, E.C.E., and Pawson, "Gillnetting (Laboratory Leaflet Number 69)", "Ministry of Agriculture, Fisheries, and Food, Directorate of Fisheries Research", 1991
  3. ↑ Animal Welfare Institute, "Driftnet Fishing", 2014
  4. ↑ Michaels, P.A., "Cooperative efforts dealing with driftnet fishing" Archived 2008-05-09 at the Wayback Machine , 2006
  5. ↑ Miller, G. Tyler (2004). Living in the Environment. Pacific Grove, CA: Brooks/Cole. p. 302. ISBN   0-534-27411-0.
  6. ↑ Davies, R.W.D., "Defining and estimating global marine fisheries bycatch", "Marine Policy", 2009
  7. ↑ Soykan, C.U. et al., "Why study bycatch? An introduction to the Theme Section on fisheries bycatch", "Endangered Species Research", 2008
  8. ↑ "New England/Mid-Atlantic | NOAA Fisheries". 20 July 2021.
  9. ↑ Bonfil, R., "The problem of incidental catches of sharks and rays, its likely consequences, and some possible solutions" Archived October 7, 2011, at the Wayback Machine , "Pacific Fisheries Coalition, Shark Conference Hawaii", 2000
  10. ↑ National Geographic's Incidental Kill
  11. ↑ Hall, H. "Web Across the Currents" Archived 2011-07-18 at the Wayback Machine , 1987
  12. ↑ Zydelis, R., "Bycatch in gillnet fisheries - an overlooked threat to waterbird populations" Archived March 26, 2012, at the Wayback Machine , "Biological Conservation", 2009
  13. ↑ Murphy, S., "General information on dissolved oxygen", 2007
  14. ↑ Food and Agriculture Organization, "Ghost nets hurting marine environments" Archived 2018-08-01 at the Wayback Machine , 2009
  15. ↑ Laville, Sandra (2019-11-06). "Dumped fishing gear is biggest plastic polluter in ocean, finds report". The Guardian . Retrieved 2022-05-10.
  16. ↑ Magazine, Smithsonian; Kindy, David. "With Ropes and Nets, Fishing Fleets Contribute Significantly to Microplastic Pollution". Smithsonian Magazine. Retrieved 2022-05-10.
  17. ↑ Earth Summit, "The agreement on high seas fishing: an update" Archived August 17, 2011, at the Wayback Machine , "United Nations Department of Public Information", 1997
  18. ↑ Spalding, M., "Saving the high seas" Archived July 2, 2010, at the Wayback Machine , 2008
  19. ↑ Marine Stewardship Council
  20. ↑ Monterey Bay Aquarium, "Seafood watch" Archived February 18, 2011, at the Wayback Machine ,
  21. ↑ Spalding, M., [www.misr5.com/99414/تفحيط/ "legal case study"], 2014
  22. ↑ Couch AJ, Dyer F, Lintermans M, Ross-Magee P. (2016) Drift net performance for larval fish sampling in rivers. PeerJ Preprints 4:e2416v1 https://peerj.com/preprints/2416/?td=wk
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