Gillnet
Encyclopedia
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Fishing industry
The fishing industry includes any industry or activity concerned with taking, culturing, processing, preserving, storing, transporting, marketing or selling fish or fish products....
and artisanal
Artisan fishing
Artisan fishing is a term used to describe small scale low-technology commercial or subsistence fishing practices. The term particularly applies to coastal or island ethnic groups using traditional techniques such as rod and tackle, arrows and harpoons, throw nets and drag nets, and traditional...
fishermen of all the oceans and in some freshwater and estuary areas. The gillnet also is used by fisheries scientists
Fisheries science
Fisheries science is the academic discipline of managing and understanding fisheries. It is a multidisciplinary science, which draws on the disciplines of oceanography, marine biology, marine conservation, ecology, population dynamics, economics and management to attempt to provide an integrated...
to monitor fish populations. Because gillnets can be so effective their use is closely monitored and regulated by fisheries management and enforcement agencies. Mesh size, twine strength, as well as net length and depth are all closely regulated to reduce bycatch
Bycatch
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...
of non-target species. Most salmon fisheries in particular have an extremely low incidence of catching non-target species.
Gillnet, the name of the net
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...
employed, illustrates the method used to snare target fish. They try to swim through deliberately sized mesh openings but are unable to squeeze through swimming forward. Once in this position, they are prevented from backing out due to the tendency for their gills to become caught. This effectively captures them until they are removed by the fisher.
History
- See also: History of fishingHistory of fishingFishing is the activity of catching fish. It is an ancient practice dating back at least 40,000 years. Since the 16th century fishing vessels have been able to cross oceans in pursuit of fish and since the 19th century it has been possible to use larger vessels and in some cases process the fish on...
Gillnets existed in ancient times as archaeological evidence from the Middle East demonstrates. In North America, aboriginal fishermen used cedar canoes and natural fiber nets, e.g., made with nettels or the inner bark of cedar. They would attach stones to the bottom of the nets as weights, and pieces of wood to the top, to use as floats. This allowed the net to suspend straight up and down in the water. Each net would be suspended either from shore or between two boats. Native fishers in the Pacific Northwest, Canada, and Alaska still commonly use gillnets in their fisheries for salmon
Salmon
Salmon is the common name for several species of fish in the family Salmonidae. Several other fish in the same family are called trout; the difference is often said to be that salmon migrate and trout are resident, but this distinction does not strictly hold true...
and steelhead.
Both drift gillnets and setnets also have been widely adapted in cultures around the world. The antiquity of gillnet technology is documented by a number of sources from many countries and cultures. Japanese
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...
records trace fisheries exploitation, including gillnetting, for over 3,000 years. Many relevant details are available concerning the Edo period
Edo period
The , or , is a division of Japanese history which was ruled by the shoguns of the Tokugawa family, running from 1603 to 1868. The political entity of this period was the Tokugawa shogunate....
(1603-1868). Fisheries in the Shetland Islands, which were settled by Norsemen
Norsemen
Norsemen is used to refer to the group of people as a whole who spoke what is now called the Old Norse language belonging to the North Germanic branch of Indo-European languages, especially Norwegian, Icelandic, Faroese, Swedish and Danish in their earlier forms.The meaning of Norseman was "people...
during the Viking
Viking
The term Viking is customarily used to refer to the Norse explorers, warriors, merchants, and pirates who raided, traded, explored and settled in wide areas of Europe, Asia and the North Atlantic islands from the late 8th to the mid-11th century.These Norsemen used their famed longships to...
era, share cultural and technological similarities with Norwegian fisheries, including gillnet fisheries for herring. Many of the Norwegian immigrant fishermen who came to fish in the great Columbia River salmon fishery during the second half of the 19th century did so because they had experience in the gillnet fishery for cod in the waters surrounding the Lofoten
Lofoten
Lofoten is an archipelago and a traditional district in the county of Nordland, Norway. Though lying within the Arctic Circle, the archipelago experiences one of the world's largest elevated temperature anomalies relative to its high latitude.-Etymology:...
Islands of northern Norway
Norway
Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...
. Gillnets were used as part of the seasonal round by Swedish
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
fishermen as well. Welsh and English fishermen gillnetted for Atlantic salmon in the rivers of Wales
Wales
Wales is a country that is part of the United Kingdom and the island of Great Britain, bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km²...
and England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
in coracles
Coracle
The coracle is a small, lightweight boat of the sort traditionally used in Wales but also in parts of Western and South Western England, Ireland , and Scotland ; the word is also used of similar boats found in India, Vietnam, Iraq and Tibet...
, using hand-made nets, for at least several centuries. These are but a few of the examples of historic gillnet fisheries around the world.
Gillnetting was an early fishing technology in Colonial America, used for example, in fisheries for Atlantic salmon and shad. Immigrant fishermen from northern Europe and the Mediterranean brought a number of different adaptations of the technology from their respective homelands with them to the rapidly expanding salmon fisheries of the Columbia River from the 1860s forward. The boats used by these fisherman were typically around 25 feet (8 m) long and powered by oars. Many of these boats also had small sails and were called "row-sail" boats. At the beginning of the 1900s, steam powered ships would haul these smaller boats to their fishing grounds and retrieve them at the end of each day. However, at this time gas powered boats were beginning to make their appearance, and by the 1930s, the row-sail boat had virtually disappeared, except in Bristol Bay, Alaska, where motors were prohibited in the gillnet fishery by territorial law until 1951.
In 1931, the first powered drum was created by Laurie Jarelainen. The drum is a circular device that is set to the side of the boat and draws in the nets. The powered drum allowed the nets to be drawn in much faster and along with the faster gas powered boats, fisherman were able to fish in areas they had previously been unable to go into, thereby revolutionizing the fishing industry.
During World War II, navigation and communication devices, as well as many other forms of maritime equipment (ex. depth-sounding and radar) were improved and made more compact. These devices became much more accessible to the average fisherman, thus making their range and mobility increasingly larger. It also served to make the industry much more competitive, as the fisherman were forced to invest more in boats and equipment to stay current with developing technology.
The introduction of fine synthetic fibres such as nylon
Nylon
Nylon is a generic designation for a family of synthetic polymers known generically as polyamides, first produced on February 28, 1935, by Wallace Carothers at DuPont's research facility at the DuPont Experimental Station...
in the construction of fishing gear during the 1960s marked an expansion in the commercial use of gillnets. The new materials were cheaper and easier to handle, lasted longer and required less maintenance than natural fibres. In addition, multifilament nylon
Multifilament fishing line
Multifilament line, also referred to as The Super Lines, is a type of fishing line. It is a braided line which is made up of a type of polyethylene, an extremely thin line for its strength. By weight, polyethylene strands are five to ten times sturdier than steel...
, monofilament or multimonofilament fibres
Braided fishing line
Braided line was one of the of earliest types of fishing line, and in its modern incarnations it is still very popular in some situations because of its high knot strength, lack of stretch, and great overall power in relation to its diameter...
become almost invisible in water, so nets made with synthetic twines generally caught greater numbers of fish than natural fibre nets used in comparable situations.
Nylon is highly resistant to abrasion and degradation, hence the netting has the potential to last for many years if it is not recovered. This ghost fishing is of environmental concern. Attaching the gillnet floats with biodegradable material can reduce the problem. However it is difficult to generalize about the longevity of ghost-fishing gillnets due to the varying environments in which they are used. Some researchers have found gill-nets still catching fish and crustaceans over a year after loss, while others have found lost nets destroyed by wave action within one month or overgrown with seaweed
Seaweed
Seaweed is a loose, colloquial term encompassing macroscopic, multicellular, benthic marine algae. The term includes some members of the red, brown and green algae...
s, increasing their visibility and reducing their catching potential to such an extent that they became a microhabitat used by small fish.
This type of net was heavily used by many 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, South Korean, and Taiwan
Taiwan
Taiwan , also known, especially in the past, as Formosa , is the largest island of the same-named island group of East Asia in the western Pacific Ocean and located off the southeastern coast of mainland China. The island forms over 99% of the current territory of the Republic of China following...
ese fishing fleets on the high seas in the 1980s to target 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...
s. Although highly selective with respect to size class of animals captured, gillnets are associated with high numbers of incidental captures of cetacea
Cetacea
The order Cetacea includes the marine mammals commonly known as whales, dolphins, and porpoises. Cetus is Latin and is used in biological names to mean "whale"; its original meaning, "large sea animal", was more general. It comes from Ancient Greek , meaning "whale" or "any huge fish or sea...
ns (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 and 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). In the Sri Lankan gillnet fishery, one dolphin is caught for every 1.7-4.0 tonnes of tuna landed. This compares poorly with the rate of one dolphin per 70 tonnes of tuna landed in the eastern Pacific purse seine tuna fishery.
Legal status
United Nations General AssemblyUnited 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...
Resolution 46/215 called for the cessation of all "large-scale pelagic drift-net fishing" in 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,...
by the end of 1992. The laws of individual countries vary with regard to fishing in waters under their jurisdiction.
Possession of gillnets is illegal in some U.S. states.
Selectivity
Ogive
An ogive is the roundly tapered end of a two-dimensional or three-dimensional object.-Applied physical science and engineering:In ballistics or aerodynamics, an ogive is a pointed, curved surface mainly used to form the approximately streamlined nose of a bullet or other projectile.The traditional...
that is skewed towards medium sized fishes, unlike active gears such as trawling
Trawling
Trawling is a method of fishing that involves pulling a fishing net through the water behind one or more boats. The net that is used for trawling is called a trawl....
, in which the proportion of fish entering the net that are retained increases with length.
Commercial gillnet fisheries are still an important method of harvesting salmon in Alaska, British Columbia, Washington, and Oregon. In the Columbia River
Columbia River
The Columbia River is the largest river in the Pacific Northwest region of North America. The river rises in the Rocky Mountains of British Columbia, Canada, flows northwest and then south into the U.S. state of Washington, then turns west to form most of the border between Washington and the state...
, non-Indian commercial salmon fisheries for spring chinook have developed methods of selectively harvesting adipose fin clipped hatchery salmon using small mesh gillnets known as tangle net
Tangle 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,...
s or tooth nets. Non-fin clipped (primarily natural origin salmon) must be released. Fishery management agencies estimate a relatively low release mortality rate on salmon and steelhead released from these small mesh gillnets.
Gillnets are sometimes a controversial gear type especially among sport fishers who sometimes argue they are inappropriate especially for salmon fisheries. Most salmon fisheries are strictly managed to minimize total impacts to specific populations and salmon fishery managers continue to allow their use.
Alternatives
Given the selective properties of gillnet fishing, alternative methods of harvest are currently being studied. Recent WDF&W reports suggest that purse seine is the most productive method with having highest catch per unit effortCatch per unit effort
In fisheries and conservation biology, the catch per unit effort is an indirect measure of the abundance of a target species. Changes in the catch per unit effort are inferred to signify changes to the target species' true abundance...
(CPUE), but has little information on the effectiveness of selectively harvesting hatchery-reared salmon . More conclusive research has been conducted jointly between the Confederated Tribes of the Colville Reservation and Bonneville Power Administration on a 10-year study on selective harvest methods of hatchery origin salmon in the Upper Columbia River by purse seine and tangle net. Their 2009 and 2010 findings show that purse seines have a higher percentage of survivability and higher CPUE than does tangle nets . A Colville Tribe biologist reports that during these two years the tribe harvested 3,163 hatchery Chinook while releasing 2,346 wild Chinook with only 1.4% direct or immediate mortality using purse seines , whereas the tangle net was far less productive but had an approximate 12.5% mortality. Researchers commented that the use of recovery boxes and shortened periods between checking the nets would have likely decreased mortality rates. While there is data that shows success of selective methods of harvest at protecting wild and ESA listed salmon, there still must be social acceptance of new methods of fishing.
Set gillnets
Set gillnets consist of a single netting wall kept vertical by a floatline (upper line/headrope) and a weighted groundline (lower line/footrope). Small floats, usually shaped like eggs or cylinders and made of solid plastic, are evenly distributed along the floatline, while lead weights are evenly distributed along groundline. The lower line can also be made of lead cored rope, which does not need additional weight. The net is set on the bottom, or at a distance above it and held in place with anchors or weights on both ends. By adjusting the design these nets can fish in surface layers, in mid water or at the bottom, targeting pelagic, demersal or benthic species. On small boats gillnets are handled by hand. Larger boats use hydraulic net haulers or net drums. Set gillnets are widely used all over the world, and are employed both in inland and sea waters. They are popular with artisanal fisheriesArtisan fishing
Artisan fishing is a term used to describe small scale low-technology commercial or subsistence fishing practices. The term particularly applies to coastal or island ethnic groups using traditional techniques such as rod and tackle, arrows and harpoons, throw nets and drag nets, and traditional...
because no specialized gear is needed, and it is low cost based on the relationship of fuel/fish.
Encircling gillnets
Encircling gillnets are gillnets set vertically in shallow water, with the floatline remaining at the surface so they encircle fish. Small open boats or canoes can be used to set the net around the fish. Once the fish are encircled, the fishers shout and splash the water to panic the fish so they gill or entangle themselves. There is little negative impact on the environment. As soon as the gear is set the scaring takes place and the net is hauled back in. The fish are alive and discardsDiscards
Discards are the portion of a catch of fish which is not retained on board during commercial fishing operations and is returned, often dead or dying, to the sea...
can be returned to the sea. Encircling gillnets are commonly used by groups of small-scale fishers, and does not require other equipment.
Combined gillnets-trammel nets
This bottom-set gear has two parts:- the upper part is a standard gillnet where semi-demersal or pelagic fishPelagic fishPelagic 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...
can be gilled - the lower part is a trammel net where bottom fish can entangle.
The combined nets are maintained more or less vertically in the usual way by floats on the floatline and weights on the groundline. They are set on the bottom. After a time depending on the target species, they are hauled on board. Traditional combined nets were hauled by hand, especially on smaller boats. Recent hydraulic driven net haulers are now common. The gilled, entangled and enmeshed fish are removed from the net by hand. Of some concern with this method is ghost fishing by lost nets and bycatch
Bycatch
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...
of diving seabirds. Nets combined in this way were first used in the Mediterranean.
Drift nets
A drift net consists of one or more panels of webbing fastened together. They are left free to drift with the current, usually near the surface or not far below it. Floats on the floatline and weights on the groundline keep them vertical. Drift nets drift with the current while they are connected with the operating vessel, the driftnetter or drifterDrifter (fishing boat)
A drifter is a type of fishing boat. They were designed to catch herrings in a long drift net. Herring fishing using drifters has a long history in the Netherlands and in many British fishing ports, particularly in East Scottish ports....
.
Drift nets are usually used to catch schooling
Shoaling and schooling
In biology, any group of fish that stay together for social reasons are said to be shoaling , and if, in addition, the group is swimming in the same direction in a coordinated manner, they are said to be schooling . In common usage, the terms are sometimes used rather loosely...
forage fish
Forage fish
Forage fish, also called prey fish or bait fish, are small fish which are preyed on by larger predators for food. Predators include other larger fish, seabirds and marine mammals. Typical ocean forage fish feed near the base of the food chain on plankton, often by filter feeding...
such as herring
Herring
Herring is an oily fish of the genus Clupea, found in the shallow, temperate waters of the North Pacific and the North Atlantic oceans, including the Baltic Sea. Three species of Clupea are recognized. The main taxa, the Atlantic herring and the Pacific herring may each be divided into subspecies...
and sardine
Sardine
Sardines, or pilchards, are several types of small, oily fish related to herrings, family Clupeidae. Sardines are named after the Mediterranean island of Sardinia, around which they were once abundant....
s, and also larger 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...
such as 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...
, salmon
Salmon
Salmon is the common name for several species of fish in the family Salmonidae. Several other fish in the same family are called trout; the difference is often said to be that salmon migrate and trout are resident, but this distinction does not strictly hold true...
and pelagic 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...
. Net haulers are usually used to set and haul driftnets, with a drifter capstan on the forepart of the vessel. In developing countries most nets are hauled by hand. The mesh size of the gillnets is very effective at selecting or regulating the size of fish caught. The drift net has a low fuel/fish energy consumption compared to other fishing gear. However, the issue of concern with this type of net is the bycatch
Bycatch
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...
of species that are not targeted, such as marine mammals, seabirds and to a minor extent turtles. The use of drift nets longer than 2.5 kilometres on the high seas was banned by the United Nations in 1991. Prior to this ban, drift nets were reaching lengths of 60 kilometres. However, there are still serious concerns with ongoing violations.
Gillnets and entangling nets
The tangle net, or tooth net, originated in British Columbia, Canada, as a gear specifically developed for selective fisheries. Tangle nets have smaller mesh sizes than standard gillnets. They are designed to catch fish by their nose or jaw, enabling bycatch to be resuscitated and released unharmed. Tangle nets as adapted to the mark-selective fishery for spring Chinook salmon on the lower Columbia River have a standard mesh size of 4-1/4 inches (10.8 cm.). Short net lengths and soak times are used in an effort to land fish in good condition. Only fish marked by an adipose fin-clip may be retained. All fish retaining their adipose fins must be returned to the water. Tangle nets are used in conjunction with a live recovery box, which acts as a resuscitation chamber for unmarked fish that appear lethargic or stressed before their release into the water.External links
- Video: Gillnets in Operation
- Video: Gillnetting the Copper River Delta, Alaska
- Video: Tangle Net Fishing on the Columbia River
- Manual on estimation of selectivity for gillnet and longline gears in abundance surveys - report for Food and Agriculture Organisation of the United Nations, 2000.
- http://www.seawatch.org/position_papers/gillnet.php