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Bycatch (or by-catch), in the
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. It is defined by the Food and Agriculture Organization as including ...
, is a
fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. Included in this definition are the living hagfish, lampreys, and Chondrichthyes, cartilaginous and bony fish as we ...
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 Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military ...
species (
freshwater fish Freshwater fish are those that spend some or all of their lives in fresh water, such as rivers and lakes, with a salinity of less than 1.05%. These environments differ from marine conditions in many ways, especially the difference in levels o ...
not saltwater fish) that are caught (either intentionally or unintentionally) but regarded as generally "undesirable" are referred to as " rough fish" (mainly US) and " coarse fish" (mainly UK). In 1997, the Organisation for Economic Co-operation and Development (OECD) defined bycatch as "total fishing mortality, excluding that accounted directly by the retained catch of target species". Bycatch contributes to fishery decline and is a mechanism of overfishing for unintentional catch. The average annual bycatch rate of
pinniped Pinnipeds (pronounced ), commonly known as seals, are a widely distributed and diverse clade of carnivorous, fin-footed, semiaquatic, mostly marine mammals. They comprise the extant families Odobenidae (whose only living member is the ...
s and cetaceans in the US from 1990 to 1999 was estimated at 6215 animals with a standard error of 448. Bycatch issues originated with the "mortality of dolphins in tuna nets in the 1960s". There are at least four different ways the word "bycatch" is used in fisheries: * Catch which is retained and sold but which is not the target species for the fishery * Species/sizes/sexes of fish which fishers discard * Non-target fish, whether retained and sold or discarded * Unwanted
invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chorda ...
species, such as
echinoderm An echinoderm () is any member of the phylum Echinodermata (). The adults are recognisable by their (usually five-point) radial symmetry, and include starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers, as well as the ...
s and non-commercial
crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapoda, decapods, ostracoda, seed shrimp, branchiopoda, branchiopods, argulidae, fish lice, krill, remipedes, isopoda, isopods, barnacles, copepods, ...
s, and various vulnerable species groups, including seabirds, sea turtles, marine mammals and elasmobranchs (sharks and their relatives). Additionally, the term "deliberate bycatch" is used to refer to bycatch as a source of illegal wildlife trade (IWT) in several areas throughout world. There are several tools to estimate bycatch limits--the maximum number of animals that could be sustainably removed from a population impacted by bycatch. These include the 'potential biological removal' (PBR) and the 'sustainable anthropogenic mortality in stochastic environments' (SAMSE), which incorporates stochastic factors to determine sustainable limits to bycatch and other human-caused mortality of wildlife.


Examples


Recreational fishing

Given the popularity of recreational fishing throughout the world, a small local study in the US in 2013 suggested that discards may be an important unmonitored source of fish mortality.


Shrimp trawling

The highest rates of incidental catch of non-target species are associated with tropical shrimp trawling. In 1997, the Food and Agriculture Organization of the United Nations (FAO) documented the estimated bycatch and discard levels from shrimp fisheries around the world. They found discard rates (bycatch to catch ratios) as high as 20:1 with a world average of 5.7:1. Shrimp trawl fisheries catch two percent of the world total catch of all fish by weight, but produce more than one-third of the world total bycatch. US shrimp trawlers produce bycatch ratios between 3:1 (3 bycatch:1 shrimp) and 15:1 (15 bycatch:1 shrimp). Trawl nets in general, and shrimp trawls in particular, have been identified as sources of mortality for cetacean and finfish species.SAFMC (2004) When bycatch is discarded (returned to the sea), it is often dead or dying. Tropical shrimp trawlers often make trips of several months without coming to port. A typical haul may last four hours after which the net is pulled in. Just before it is pulled on board the net is washed by zigzagging at full speed. The contents are then dumped on deck and are sorted. An average of 5.7:1 means that for every kilogram of shrimp there are 5.7 kg of bycatch. In tropical inshore waters the bycatch usually consists of small fish. The shrimps are frozen and stored onboard; the bycatch is discarded. Recent sampling in the South Atlantic rock shrimp fishery found 166 species of finfish, 37
crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapoda, decapods, ostracoda, seed shrimp, branchiopoda, branchiopods, argulidae, fish lice, krill, remipedes, isopoda, isopods, barnacles, copepods, ...
species, and 29 other species of
invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chorda ...
among the bycatch in the trawls. Another sampling of the same fishery over a two-year period found that rock shrimp amounted to only 10% of total catch weight. Iridescent swimming crab, dusky flounder, inshore lizardfish, spot, brown shrimp, longspine swimming crabs, and other bycatch made up the rest. Despite the use of bycatch reduction devices, the shrimp fishery in the Gulf of Mexico removes about 25–45 million red snapper annually as bycatch, nearly one-half the amount taken in recreational and commercial snapper fisheries.


Cetacean

Cetaceans, such as
dolphin A dolphin is an aquatic mammal within the infraorder Cetacea. Dolphin species belong to the families Delphinidae (the oceanic dolphins), Platanistidae (the Indian river dolphins), Iniidae (the New World river dolphins), Pontoporiidae (the b ...
s, porpoises, and whales, can be seriously affected by entanglement in fishing nets and lines, or direct capture by hooks or in trawl nets. Cetacean bycatch is increasing in intensity and frequency. In some fisheries, cetaceans are captured as bycatch but then retained because of their value as food or
bait Bait may refer to: General * Bait (luring substance), bait as a luring substance ** Fishing bait, bait used for fishing Film * ''Bait'' (1950 film), a British crime film by Frank Richardson * ''Bait'' (1954 film), an American noir film by Hugo ...
. In this fashion, cetaceans can become a target of fisheries. One example of bycatch is dolphins caught in
tuna A tuna is a saltwater fish that belongs to the tribe Thunnini, a subgrouping of the Scombridae (mackerel) family. The Thunnini comprise 15 species across five genera, the sizes of which vary greatly, ranging from the bullet tuna (max length: ...
nets. As dolphins are mammals and do not have
gill A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they ar ...
s, they may drown while stuck in nets underwater. This bycatch issue has been one of the reasons of the growing ecolabelling industry, where fish producers mark their packagings with disclaimers such as "dolphin friendly" to reassure buyers. However, "dolphin friendly" does not mean that dolphins were not killed in the production of a particular tin of tuna, but that the fleet which caught the tuna did not ''specifically'' target a feeding pod of dolphins, but relied on other methods to spot tuna schools. The bycatch of the
Caspian seal The Caspian seal (''Pusa caspica'', syn. ''Phoca caspica'') is one of the smallest members of the earless seal family and unique in that it is found exclusively in the brackish Caspian Sea. It lives along the shorelines, but also on the many roc ...
may be recognized as the one of the biggest entanglements of pinnipeds as bycatch in the world


Albatross

Of the 21 albatross species recognised by IUCN on their Red List, 19 are threatened, and the other two are near threatened. Two species are considered critically
endangered An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching and in ...
: the
Amsterdam albatross The Amsterdam albatross or Amsterdam Island albatross, (''Diomedea amsterdamensis''), is a large albatross which breeds only on Amsterdam Island in the southern Indian Ocean. It was only described in 1983, and was thought by some researchers to ...
and the Chatham albatross. One of the main threats is commercial long-line fishing, because albatrosses and other
seabird Seabirds (also known as marine birds) are birds that are 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 envir ...
s which readily feed on offal are attracted to the set bait, after which they become hooked on the lines and drown. An estimated 100,000 albatross per year are killed in this fashion. Unregulated pirate fisheries exacerbate the problem.


Sea turtles

Sea turtle Sea turtles (superfamily Chelonioidea), sometimes called marine turtles, are reptiles of the order Testudines and of the suborder Cryptodira. The seven existing species of sea turtles are the flatback, green, hawksbill, leatherback, loggerhe ...
s, already critically endangered, have been killed in large numbers in shrimp trawl nets. Estimates indicate that thousands of
Kemp's ridley Kemp's ridley sea turtle (''Lepidochelys kempii''), also called the Atlantic ridley sea turtle, is the rarest species of sea turtle and is the world's most endangered species of sea turtle. It is one of two living species in the genus '' Lepido ...
,
loggerhead Loggerhead or Loggerheads may refer to: Places * Loggerheads, Denbighshire, a village in Denbighshire, Wales * Loggerheads, Staffordshire, a small village in north Staffordshire, England * Loggerhead Key, the largest islet in the Dry Tortugas, F ...
,
green Green is the color between cyan and yellow on the visible spectrum. It is evoked by light which has a dominant wavelength of roughly 495570 nm. In subtractive color systems, used in painting and color printing, it is created by a combin ...
, and
leatherback sea turtle The leatherback sea turtle (''Dermochelys coriacea''), sometimes called the lute turtle or leathery turtle or simply the luth, is the largest of all living turtles and the heaviest non-crocodilian reptile, reaching lengths of up to and weight ...
s are caught in shrimp trawl fisheries in the
Gulf of Mexico The Gulf of Mexico ( es, Golfo de México) is an ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of the United ...
and the US
Atlantic The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...
annually The speed and length of the trawl method is significant because, "for a tow duration of less than 10 minutes, the mortality rate for sea turtles is less than one percent, whereas for tows greater than sixty minutes the mortality rate rapidly increases to fifty to one hundred percent". Sea turtles can sometimes escape from the trawls. In the Gulf of Mexico, the Kemp’s ridley turtles recorded most interactions, followed in order by loggerhead, green, and leatherback sea turtles. In the US Atlantic, the interactions were greatest for loggerheads, followed in order by Kemp’s ridley, leatherback, and green sea turtles.


Fishing gear

Bycatch is inevitable wherever there is fishing. The incidental catch is not limited to only fish species: dolphins, sea turtles, and seabirds are also victims of bycatch. Longlines, trawls and
purse seine Seine fishing (or seine-haul fishing; ) is a method of fishing that employs a surrounding net, called a seine, that hangs vertically in the water with its bottom edge held down by weights and its top edge buoyed by floats. Seine nets can be de ...
nets are driving factors in the endangerment of no fewer than fifteen shark species. Bycatch may also affect reproduction of populations as juveniles are also victims of bycatch. Bycatch happens most commonly with the use of gillnetting, longlines, or bottom trawling. Longlines with bait hook attachments can potentially reach lengths of dozens of kilometres, and, along with gill nets in the water and bottom trawls sweeping the sea floor, can catch essentially everything in their path. There are thousands of kilometres of nets and lines cast into the world's oceans daily. This modern fish gear is robust and invisible to the eye, making it efficient at catching fish and bycatching everything that happens to be in the way. Hook-and-line fishing could limit bycatch to a certain extent as the non-target animals can be released back to the ocean fairly quickly.


Mitigation

Concern about bycatch has led fishers and scientists to seek ways of reducing unwanted catch. There are two main approaches. One approach is to ban fishing in areas where bycatch is unacceptably high. Such area closures can be permanent, seasonal, or for a specific period when a bycatch problem is registered. Temporary area closures are common in some bottom trawl fisheries where undersized fish or non-target species are caught unpredictably. In some cases fishers are required to relocate when a bycatch problem occurs. The other approach is alternative fishing gear. A technically simple solution is to use nets with a larger mesh size, allowing smaller species and smaller individuals to escape. However, this usually requires replacing the existing gear. In some cases, it is possible to modify gear. Bycatch reduction devices (BRDs) and the Nordmore grate are net modifications that help fish escape from shrimp nets. BRDs allow many commercial finfish species to escape. The US government has approved BRDs that reduce finfish bycatch by 30%.
Spanish mackerel Scomberomorini is a tribe of ray-finned saltwater bony fishes that is commonly known as the Spanish mackerels, seerfishes or seer fish. This fish closely resembles the King Mackerel. This tribe is a subset of the mackerel family (Scombridae) ...
and weakfish bycatch in the South Atlantic was reduced by 40%. However, recent surveys suggest BRDs may be less effective than previously thought.Gulf of Mexico Fishery Management Council (GMFMC) (2006
''Scoping Document for Amendment 15 to the Shrimp FMP''
A rock shrimp fishery off Florida found the devices did not exclude 166 species of fish, 37 crustacean species, and 29 species of other invertebrates. In 1978, the
National Marine Fisheries Service The National Marine Fisheries Service (NMFS), informally known as NOAA Fisheries, is a United States federal agency within the U.S. Department of Commerce's National Oceanic and Atmospheric Administration (NOAA) that is responsible for the stew ...
(NMFS) started to develop turtle excluder devices (TED). A TED uses a grid which deflects turtles and other big animals, so they exit from the trawl net through an opening above the grid. US shrimp trawlers and foreign fleets which market shrimp in the US are required to use TEDs. Not all nations enforce the use of TEDs. For the most part, when they are used, TEDs have been successful reducing sea turtle bycatch. However, they are not completely effective, and some turtles are still captured. NMFS certifies TED designs if they are 97% effective. In heavily trawled areas, the same sea turtle may pass repeatedly through TEDs. Recent studies indicate recapture rates of 20% or more, but it is not clear how many turtles survive the escape process. The size selectivity of trawl nets is controlled by the size of the net openings, especially in the "cod end". The larger the openings, the more easily small fish can escape. The development and testing of modifications to fishing gear to improve selectivity and decrease impact is called "conservation engineering".
Longline fishing 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''.Hawaii Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only stat ...
longline swordfish fishing season was closed due to excessive loggerhead sea turtle bycatch after being open only a few months, despite using modified circle hooks. One solution that Norway came up with to reduce bycatch is to, "adopt a 'no discards' policy". This means that the fishermen must keep everything they catch. This policy has helped to "encourage bycatch research", which, in turn has helped "encourage behavioral changes in fishers" and "reduce the waste of life" as well. Seabirds get entangled in longlines by flocking around vessels, this eventually leads to drowning because they try to catch baits on the hooks. Fisheries had been using "streamer lines" as a cost effective solution to mitigate this type of bycatch, and it has dramatically reduced seabird mortality. These streamer lines have bright colors and are made of polyester rope, they are positioned alongside the longlines on both sides. Their bright colors and constantly flapping of water frightens the seabirds and they fly away before reaching the baited hooks. A successful example would be the use of streamer lines in Alaskan
groundfish Demersal fish, also known as groundfish, live and feed on or near the bottom of seas or lakes (the demersal zone).Walrond Carl . "Coastal fish - Fish of the open sea floor"Te Ara - the Encyclopedia of New Zealand. Updated 2 March 2009 They oc ...
longline fisheries, as the deaths of seabirds declined by about 70% after the employment of these lines.


Alternative to discarding

Some fisheries retain bycatch, rather than throwing the fish back into the ocean. Sometimes bycatch is sorted and sold as food, especially in Asia, Africa and Latin America, where cost of labour is cheaper. Bycatch can also be sold in frozen bags as "assorted seafood" or "seafood medley" at cheaper prices. Bycatch can be converted into fish hydrolysate (ground up fish carcasses) for use as a soil amendment in organic agriculture or it can be used as an ingredient in
fish meal Fish meal is a commercial product made from whole wild-caught fish, bycatch and fish by-products to feed farm animals, e.g., pigs, poultry, and farmed fish.R. D. Miles and F. A. Chapman.FA122: The Benefits of Fish Meal in Aquaculture DietsFisher ...
. In
Southeast Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia, South-eastern Asia or SEA, is the geographical south-eastern region of Asia, consisting of the regions that are situated south of mainland ...
bycatch is sometimes used as a raw material for fish sauce production. Bycatch is also commonly de-boned, de-shelled, ground and blended into fish paste or moulded into fish cakes (
surimi is a paste made from fish or other meat. The term can also refer to a number of East Asian foods that use that paste as their primary ingredient. It is available in many shapes, forms, and textures, and is often used to mimic the texture and ...
) and sold either fresh (for domestic use) or frozen (for export). This is commonly the case in Asia or by Asian fisheries. Sometimes bycatch is sold to fish farms to feed farmed fish, especially in Asia.


Non-fisheries bycatch

The term "bycatch" is used also in contexts other than fisheries. Examples are insect collecting with pitfall traps or
flight interception trap A flight interception trap (or FIT) is a widely used trapping, killing, and preserving system for flying insects. It is especially well-suited for collecting beetles, since these animals usually drop themselves after flying into an object,
s for either financial, controlling or scientific purposes (where the bycatch may either be small vertebrates or untargeted insects) and control of introduced vertebrates which have become pest species like the muskrat in Europe (where the bycatch in traps may be European minksKranz A, Polednik L and Gotea V (2001
Conservation of the European Mink (''Mustella lutreila'') in the Danube Delta
Background information and project plan. ''Scientific Annals of the Danube Delta Institute for Research and Development'', Tulcea, 2000–2001.
or
waterfowl Anseriformes is an order of birds also known as waterfowl that comprises about 180 living species of birds in three families: Anhimidae (three species of screamers), Anseranatidae (the magpie goose), and Anatidae, the largest family, which ...
).


See also

* Environmental stewardship *
Discards 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. The practice of discarding is driven by economic and political factors; fish which are ...
*
Cetacean bycatch Cetacean bycatch (or cetacean by-catch) is the incidental capture of non-target cetacean species such as dolphins, porpoises, and whales by fisheries.Alverson et al. (1994) Bycatch can be caused by entanglement in fishing nets and lines, or di ...
* List of environmental issues * Shrimp turtle case * Ghost net


References


Further reading

* FAO (2009) ''Technical Guidelines for Responsible Fisheries'', Number 1: Fishing operations, supplement
Best practices to reduce incidental catch of seabirds in capture fisheries
Rome. . * FAO (1997) ''A STUDY OF THE OPTIONS FOR UTILIZATION OF BYCATCH AND DISCARDS FROM MARINE CAPTURE FISHERIES'

* Karp WA, Desfosse LL and Brooke SG (2011

National Marine Fisheries Service, NOAA Technical Memo NMFS-F/SPO-117E. * SAFMC (1998
''Final Habitat Plan for the South Atlantic Region''
Essential Fish Habitat Requirements for Fishery. Management Plans of the South Atlantic Fishery Management Council. The Shrimp Fishery Management Plan (FMP), the Red Drum FMP, the Snapper Grouper FMP, the Coastal Migratory Pelagics FMP, the Golden Crab FMP, the Spiny Lobster FMP, the Coral, Coral Reefs, and Live/Hard Bottom Habitat FMP, the Sargassum Habitat FMP, and the Calico Scallop FMP.

– Blue Ocean Institute. Retrieved 22 March 2008.


External links


Mitigating Adverse Ecological impacts of open oceanfisheries – European project MADE (28 minute film)Bycatch – Smithsonian Ocean PortalBycatch Management Information System – mitigation techniques, species ID & safe handling, regulations, curated literatureLenfest Ocean Program publication on regional governance of bycatch in tuna fisheriesProject GLOBAL: Global Bycatch Assessment of Long-Lived Species projectOceana facts about bycatch/dirty fishingGreenpeace facts about bycatchAlaska Marine Conservation Council
* Johnson, Douglas H; Shaffer, Terry L and Gould, Patrick J (1990

U.S. Geological Survey. * Valdemarsen, John

UN Atlas of the Oceans: Fishery Technology Service. {{Authority control Environmental impact of fishing Bird mortality