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Information about Bycatch

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A Dall's Porpoise caught in a fishing net
In fisheries science, by-catch includes species caught in a fishery intended to target another species, as well as reproductively-immature juveniles of the target species. OECD (1997) defines bycatch as Total fishing mortality excluding that accounted directly by the retained catch of target species. According to Alverson et al. (1994) there are at least four different uses of the word by-catch in fisheries.
  • By-catch may refer to catch which is retained and sold but which is not the target species for the fishery.
  • Particularly the Northeast and Western Pacific and in American legislation bycatch means species/sizes/sexes of fish which are discarded.
  • By-catch is used on all non-target fish whether retained and sold or discarded (Hall, 1996)
  • Unwanted invertebrate species such as echinoderms and non-commercial crustaceans.

Overview

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Shrimp by-catch
One example of by-catch is dolphins caught in tuna nets. As dolphins are mammals and do not have gills they may drown while stuck in nets underwater. This by-catch issue has been one of the reasons of the growing ecolabelling industry, where fish producers mark their packagings with something like "Dolphin Friendly" to reassure buyers. Unfortunately for the dolphins, "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.

According to the U.S. National Marine Fisheries Service, in the Gulf of Mexico, three pounds of bycatch are caught for every pound of shrimp that goes to market. According to the Worldwide Fund for Nature, in the Gulf of Thailand it can be 14 pounds of bycatch per pound of shrimp. Bycatch is often discarded dead or dying by the time it is returned to the sea. Trawl nets in general, and shrimp trawls in particular, have been identified as sources of mortality for species of concern, including cetaceans. Sea turtles, already critically endangered, have been killed by the thousands in shrimp trawl nets.

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A turtle excluder device.
Concerns about bycatch have led fishermen and scientists to develop devices they can put on their nets to reduce unwanted catch. The "bycatch reduction device" (BRD) and the Nordmore grate are net modifications that help fish escape from shrimp nets. All U.S. shrimp trawlers—and all foreign fleets selling shrimp in the U.S—are supposed to outfit their nets with trap-door "Turtle excluder device," or TEDs, to let sea turtles escape. However, not every nation enforces TED use with equal vigor. The size selectivity of trawl nets is often controlled by the size of the openings in the net, especially in the "cod end". The larger the size of 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."

References

Alverson D L, Freeberg M K, Murawski S A and Pope J G. (1994). A global assessment of fisheries bycatch and discards. FAO Fisheries Technical Paper No 339 Rome.

Hall M A (1996) On bycatches. Reviews in Fish Biology and Fisheries vol. 6 (3) pp 319 - 352 (1996)

OECD (1997) Towards sustainable fisheries: economic aspects of the management of living marine resources. OECD Paris.

See also

External links

A fishery (plural: fisheries) is an organized effort by humans to catch fish or other aquatic species, an activity known as fishing. Generally, a fishery exists for the purpose of providing human food, although other aims are possible (such as sport or recreational
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species is one of the basic units of biological classification. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring.
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Delphinidae and Platanistoidea
Gray, 1821

Genera

See article below.
Dolphins are aquatic mammals that are closely related to whales and porpoises. There are almost forty species of dolphin in seventeen genera. They vary in size from 1.
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Tuna are several species of ocean-dwelling fish in the family Scombridae, mostly in the genus Thunnus. Some tuna are able to inhabit freshwater environs as well. Tunas are fast swimmers—they have been clocked at 77 km/h (48 mph)—and include several species that
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Mammalia
Linnaeus, 1758

Subclasses & Infraclasses
  • Subclass †Allotheria*
  • Subclass Prototheria
  • Subclass Theria

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A gill is a respiration organ that functions for the extraction of oxygen from water and the excretion of carbon dioxide. Unlike many small aquatic animals, which can absorb oxygen through the entire surface of their bodies, more complex aquatic organisms have gills specially
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Ecolabel is a labelling system for consumer products (including foods) that are made in fashion to avoid detrimental effects on the environment. Usually both the precautionary principle and the substitution principle are used when defining the rules for what products can be
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Pod (noun)

Pod may refer to:
  • A short (one to eight minute), user-created non-fiction video or documentary aired by Current TV
  • The seed-case of a flowering plant
  • A method of propulsion for ships also known as an Azimuth thruster

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The SHRIMP (Sensitive High Resolution Ion Microprobe) is a large-diameter, double focusing secondary ion mass spectrometer (SIMS). The SHRIMP is primarily used for geological and geochemical applications.
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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.

Sea turtles are occasionally caught as bycatch by commercial shrimp fishers.
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Cetacean bycatch is the technical term for the incidental capture of non-target cetacean species by fisheries. Species which are seriously affected by this include dolphins, porpoises, and whales.
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shrimp farm is an aquaculture business for the cultivation of marine shrimp or prawnsa for human consumption. Commercial shrimp farming began in the 1970s, and production grew steeply, particularly to match the market demands
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Incidental mortality is the death of non-fish species during the course of fishing. For instance longline and trawl fisheries can cause the death of seabirds which are attracted to the fishing vessels.
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