By-catch - AbsoluteAstronomy.com

The term “bycatch” is usually used for fish

Fish

Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

caught unintentionally in a fishery

Fishery

Generally, a fishery is an entity engaged in raising or harvesting fish which is determined by some authority to be a fishery. According to the FAO, a fishery is typically defined in terms of the "people involved, species or type of fish, area of water or seabed, method of fishing, class of boats,...

while intending to catch other fish. It may however also indicate untargeted catch in other forms of animal harvesting or collecting. Bycatch is of a different species, undersized individuals of the target species, or juveniles

Juvenile (organism)

A juvenile is an individual organism that has not yet reached its adult form, sexual maturity or size. Juveniles sometimes look very different from the adult form, particularly in terms of their colour...

of the target species.

In 1997, the Organisation for Economic Co-operation and Development (OECD) defined bycatch as “total fishing mortality

Mortality rate

Mortality rate is a measure of the number of deaths in a population, scaled to the size of that population, per unit time...

, 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.

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 fishermen
Fisherman
A fisherman or fisher is someone who captures fish and other animals from a body of water, or gathers shellfish. Worldwide, there are about 38 million commercial and subsistence fishermen and fish farmers. The term can also be applied to recreational fishermen and may be used to describe both men...

discard
Non-target fish, whether retained and sold or discarded
Unwanted invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...

species, such as echinoderms and non-commercial crustaceans, and various vulnerable species groups, including seabirds, sea turtles, marine mammals and elasmobranchs (sharks and their relatives).

Shrimp trawling

The highest rates of incidental catch of non-target species are associated with shrimp

Shrimp

Shrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...

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 1997, the Food and Agriculture Organization of the United Nations

Fão

Fão is a town in Esposende Municipality in Portugal....

(FAO) documented the estimated bycatch and discard

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...

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 2% of the world total catch of all fish by weight, but produce more than one-third of the world total bycatch. American

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

shrimp trawlers produce bycatch ratios between 3:1 (3 bycatch:1 shrimp) and 15:1(15 bycatch:1 shrimp).

Trawl nets

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 general, and shrimp trawls in particular, have been identified as sources of mortality for 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...

n and finfish species. When bycatch is discarded (returned to the sea), it is often dead or dying.

Recent sampling in the South Atlantic rock shrimp fishery found 166 species of finfish, 37 crustacean

Crustacean

Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...

species, and 29 other species of invertebrate

Invertebrate

An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...

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

Red Snapper

Red Snapper may refer to:Fish:* Several species from the genus Lutjanus, for example the red snapper .* Several species from the genus Sebastes, for example the vermilion rockfish and yelloweye rockfish Red Snapper may refer to:Fish:* Several species from the genus Lutjanus, for example the red...

annually as bycatch, nearly one half the amount taken in directed recreational and commercial snapper fisheries.

Cetacean

Cetaceans, such as 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, porpoise

Porpoise

Porpoises are small cetaceans of the family Phocoenidae; they are related to whales and dolphins. They are distinct from dolphins, although the word "porpoise" has been used to refer to any small dolphin, especially by sailors and fishermen...

s, and 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, can be seriously affected by entanglement in fishing 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...

s and lines

Fishing line

A fishing line is a cord used or made for angling. Important parameters of a fishing line are its length, material, and weight...

, or direct capture by hooks

Fish hook

A fish hook is a device for catching fish either by impaling them in the mouth or, more rarely, by snagging the body of the fish. Fish hooks have been employed for centuries by fishermen to catch fresh and saltwater fish. In 2005, the fish hook was chosen by Forbes as one of the top twenty tools...

or in trawl nets

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....

. 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

Whale meat

Whale meat is the flesh of whales used for consumption by humans or other animals. It is prepared in various ways, and is historically part of the diet and cuisine of various communities that live near an ocean, including those of Japan, Norway, Iceland, and the Arctic...

or bait

Bait fish

Bait fish are small fish caught for use as bait to attract large predatory fish, particularly game fish. Species used are typically those that are common and breed rapidly, making them easy to catch and in regular supply. Examples of marine bait fish are anchovies, halfbeaks such as ballyhoo, and...

. In this fashion, cetaceans can become a target of fisheries.

One example of bycatch is dolphin

Dolphin

s caught in 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...

nets. As dolphins are mammal

Mammal

Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s and do not have gill

Gill

A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...

s they may drown while stuck in nets underwater. This bycatch issue has been one of the reasons of the growing ecolabel

Ecolabel

Ecolabels and Green Stickers are labelling systems for food and consumer products. Ecolabels are often voluntary, but Green Stickers are mandated by law in North America for major appliances and automobiles. They are a form of sustainability measurement directed at consumers, intended to make it...

ling industry, where fish producers mark their packagings with something like "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.

Albatross

Of the 21 albatross

Albatross

Albatrosses, of the biological family Diomedeidae, are large seabirds allied to the procellariids, storm-petrels and diving-petrels in the order Procellariiformes . They range widely in the Southern Ocean and the North Pacific...

species recognised by IUCN on their Red List

IUCN Red List

The IUCN Red List of Threatened Species , founded in 1963, is the world's most comprehensive inventory of the global conservation status of biological species. The International Union for Conservation of Nature is the world's main authority on the conservation status of species...

, 19 are threatened, and the other two are near threatened. Two species are considered critically endangered

Endangered species

An endangered species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters...

: the Amsterdam Albatross

Amsterdam Albatross

The Amsterdam Albatross or Amsterdam Island Albatross, Diomedea amsterdamensis, is a huge 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 be a sub-species of the Wandering Albatross, exulans...

and the Chatham Albatross

Chatham Albatross

The Chatham Albatross, Chatham Mollymawk, or Chatham Islands Mollymawk, Thalassarche eremita, is a medium-sized black-and-white albatross which breeds only on The Pyramid, a large rock stack in the Chatham Islands, New Zealand. It is sometimes treated as a subspecies of the Shy Albatross...

. One of the main threats is commercial long-line fishing

Long-line fishing

Longline fishing is a commercial fishing technique. It uses a long line, called the main line, with baited hooks attached at intervals by means of branch lines called "snoods". A snood is a short length of line, attached to the main line using a clip or swivel, with the hook at the other end....

, because the albatrosses and other seabird

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...

s which readily feed on offal

Offal

Offal , also called, especially in the United States, variety meats or organ meats, refers to the internal organs and entrails of a butchered animal. The word does not refer to a particular list of edible organs, which varies by culture and region, but includes most internal organs other than...

are attracted to the set bait, 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 are marine reptiles that inhabit all of the world's oceans except the Arctic.-Distribution:...

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

Kemp's ridley sea turtle , or Atlantic ridley sea turtle is the rarest sea turtle and is critically endangered. It is one of two living species in the genus Lepidochelys Kemp's ridley sea turtle (Lepidochelys kempii), or Atlantic ridley sea turtle is the rarest sea turtle and is critically...

, loggerhead, green and leatherback sea turtle

Leatherback Sea Turtle

The leatherback sea turtle is the largest of all living sea turtles and the fourth largest modern reptile behind three crocodilians. It is the only living species in the genus Dermochelys. It can easily be differentiated from other modern sea turtles by its lack of a bony shell. Instead, its...

s are caught in shrimp trawl fisheries in the Gulf of Mexico

Gulf of Mexico

The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...

and the US Atlantic annually

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.

Mitigation

Concern about bycatch has led fishermen 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 under-sized fish or non-target species are caught unpredictably. In some cases fishermen 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 other cases, it is possible to modify gear. The "bycatch reduction device" (BRD) 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

Spanish mackerel

Spanish mackerel may refer to:* Chloroscombrus chrysurus* Elagatis bipinnulata* Schedophilus maculatus* Scomber japonicus* Scomberomorus brasiliensis* Scomberomorus cavalla* Scomberomorus commerson* Scomberomorus guttatus...

and weakfish

Weakfish

The weakfish, Cynoscion regalis, is a marine fish of the drum family Sciaenidae.The head and back of this fish are dark brown in color with a greenish tinge. The sides have a faint silvery hue with dusky specks, and the belly is white. The origin of its name is based on the weakness of the mouth...

bycatch in the South Atlantic was reduced by 40%. However, recent surveys suggest BRDs may be less effective than previously thought. 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

National Marine Fisheries Service

The National Marine Fisheries Service is a United States federal agency. A division of the National Oceanic and Atmospheric Administration and the Department of Commerce, NMFS is responsible for the stewardship and management of the nation's living marine resources and their habitat within the...

(NMFS) started to develop turtle excluder device

Turtle excluder device

A turtle excluder device or TED is a specialized device that allows a captured sea turtle to escape when caught in a fisherman's net.In particular, sea turtles can be caught when bottom trawling is used by the commercial shrimp fishing industry. In order to catch shrimp, a fine meshed trawl net is...

s (TEDs). 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 twenty percent 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 is controversial in some areas because of by-catch. Mitigation methods have been successfully implemented in some fisheries. These include:

weights to sink the lines quickly
streamer lines to scare birds away from baited hooks while deploying the lines
setting lines only at night with minimal ship lighting (to avoid attracting birds)
limiting fishing seasons to the southern winter (when most seabirds are not feeding young)
and not discharging offal while setting lines.

However, gear modifications do not eliminate by-catch of many species. In March 2006, the Hawaii

Hawaii

Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...

longline swordfish fishing season was closed due to excessive loggerhead sea turtle

Loggerhead sea turtle

The loggerhead sea turtle , or loggerhead, is an oceanic turtle distributed throughout the world. It is a marine reptile, belonging to the family Cheloniidae. The average loggerhead measures around long when fully grown, although larger specimens of up to have been discovered...

by-catch after being open only a few months, despite using modified circle hook

Circle hook

A circle hook is a type of fish hook which is sharply curved back in a circular shape. It has become widely popular among anglers in recent years because it hooks a much higher percentage of fish and is rarely swallowed...

Alternative to release

Some fisheries retain bycatch, rather than throwing the fish back into the ocean. In some cases bycatch may be sorted and sold as food. Bycatch can be converted into fish hydrolysate

Fish hydrolysate

Fish hydrolysate, in its simplest form, is ground up fish carcasses. After the usable portions are removed for human consumption, the remaining fish body, which means the guts, bones, cartilage, scales, meat, etc., is put into water and ground up. Some fish hydrolysate is ground more finely than...

(ground up fish carcasses) for use as a soil amendment in organic agriculture. However, if bycatch is quickly released, predators and scavengers may consume its biomass.

Non-fisheries bycatch

The term "bycatch" is used also in contexts other than fisheries. Examples are insect collecting

Insect collecting

Insect collecting is the collection of insects for hobby, scientific study or profit. Historically insect collecting has been widespread and a very popular educational hobby. Insect collecting has left traces in European cultural history, literature and songs Insect collecting is the collection of...

with pitfall trap

Pitfall trap

A pitfall trap is a trapping pit for small animals, such as insects, amphibians and reptiles. Pitfall traps are mainly used for ecology studies and ecologic pest control. Animals that enter a pitfall trap are unable to escape, and may either be killed by the trap or remain unharmed...

s or Flight Interception Trap

Flight Interception Trap

The Flight Interception Trap or FIT is a widely used trapping system for flying insects. It is especially well-suited for collecting beetles, since these animals usually drop themselves after flying into an object, rather than flying upward...

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

Muskrat

The muskrat , the only species in genus Ondatra, is a medium-sized semi-aquatic rodent native to North America, and introduced in parts of Europe, Asia, and South America. The muskrat is found in wetlands and is a very successful animal over a wide range of climates and habitats...

in Europe (where the bycatch in traps

Trap (tactic)

A trap is a device intended to catch an intruder or prey. "Trap" may also refer to the tactic of catching or harming an adversary. Conversely it may also mean a hindrance for change, being caught in a trap.-Device:*Animal trapping*Bird trapping...

may be e.g. European mink

European mink

The European mink , also known as the Russian mink, is a semi-aquatic species of Mustelid native to Europe. It is listed by the IUCN as Endangered due to an ongoing reduction in numbers, having been calculated as being more than 50% over the past three generations...

or waterfowl

Waterfowl

Waterfowl are certain wildfowl of the order Anseriformes, especially members of the family Anatidae, which includes ducks, geese, and swans....

External links

Bycatch - Smithsonian Ocean Portal
Project GLOBAL: Global Bycatch Assessment of Long-Lived Species project
Oceana facts about bycatch/dirty fishing
FAO document on bycatch and discard
Greenpeace facts about bycatch
Alaska Marine Conservation Council
Johnson, Douglas H; Shaffer, Terry L and Gould, Patrick J (1990)Incidental Catch of Marine Birds in the North Pacific High Seas Driftnet Fisheries U.S. Geological Survey.
Valdemarsen, John W catch of seabirds in longline fisheries UN Atlas of the Oceans: Fishery Technology Service.

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

Shrimp trawling

Cetacean

Albatross

Sea turtles

Mitigation

Alternative to release

Non-fisheries bycatch

See also

External links