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Bycatch are species caught in a fishery while it is intended to catch another species or reproductively-immature juveniles of the target species.

The 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 bycatch in fisheries.

• Bycatch 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.
• Bycatch 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.

Contents 1 Shrimp trawling 2 Examples 2.1 Cetacean 2.2 Albatross 2.3 Sea turtles 3 Problems and Concerns 4 Bycatch mitigation 5 See also 6 Notes 7 References 8 External links

Shrimp trawling

The highest rates of incidental catch of non-target species is associated with shrimp trawling. In 1997, the FAO documented the estimated bycatch and discard levels from shrimp fisheries around the world. They found discard rates as high as 20 pounds for every pound of shrimp, with a world average of 5.7 pounds for every pound of shrimp.¹

Worldwide, shrimp trawl fisheries generate about two percent of the world’s catch of fish in weight, but result in more than one third of the global bycatch total. In the United States, shrimp trawls produce bycatch/catch ratios (weight discarded per weight landed) between 3:1 and 15:1.²

Trawl nets in general, and shrimp trawls in particular, have been identified as sources of mortality for species of finfish and cetaceans.³ Bycatch is often discarded dead or dying by the time it is returned to the sea, and may alter food web dynamics in discarded regions.⁴

Information on bycatch in the South Atlantic Rock Shrimp fishery is limited. Recent sampling indicated 37 species of crustaceans, 166 finfish species and 29 "other" invertebrate species as bycatch in the Rock Shrimp trawl fishery.³

For example, during a two year sampling program of the South Atlantic Rock Shrimp fishery, rock shrimp accounted for only 10% of total catch by weight, with dusky flounder, iridescent swimming crab, inshore lizardfish, longspine swimming crab, spot, brown shrimp, and other bycatch species comprising the remainder.³

Despite the use of Bycatch Reduction Devices, the shrimp fishery in the Gulf of Mexico removes roughly 25-45 million Red Snapper annually as bycatch, nearly one half the amount taken in directed recreational and commercial Snapper fisheries.⁵⁶

Examples

Cetacean

Main article: Cetacean bycatch

Cetaceans, such as dolphins, 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.⁷ In some fisheries, cetaceans are captured as bycatch but then retained because of their value as food or bait.⁸ In this fashion, cetaceans can become a target of fisheries.

One example of bycatch is dolphins caught in tuna nets. As dolphins are mammals and do not have gills 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 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.

Albatross

See also: Longline fishing

Of the 21 albatross species recognised by IUCN on their Red List, 19 are threatened, and the other two are near threatened.⁹ Two species (as recognised by the IUCN) are considered critically endangered: the Amsterdam Albatross and the Chatham Albatross. One of the main threats is commercial long-line fishing,¹⁰ as the albatrosses and other seabirds which will readily feed on offal 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 turtles, already critically endangered, have been killed in large numbers in shrimp trawl nets. For example, estimates indicate that thousands of Kemp's Ridley, loggerhead, green and leatherback sea turtles are caught in shrimp trawl fisheries in the Gulf of Mexico and US Atlantic annually¹¹

Shrimp trawling has long been a significant source of sea turtle bycatch and mortality in the Gulf of Mexico and U.S. Atlantic. Within the Gulf of Mexico, Kemp’s Ridley Sea Turtles experienced the highest numbers of interactions - which can include both capture and escape from trawl gear - with shrimp trawl fisheries, followed by Loggerhead, Green, and Leatherback Sea Turtles. In the Atlantic, interactions were highest for Loggerheads, followed by Kemp’s Ridley, Leatherback, and Green Sea Turtles.¹¹

Problems and Concerns

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First of all, bycatch mortality rate is not measured, which means that more catch can be lost than what we know or can predict. For every four pounds of fish they catch, fishers worldwide throw away more than one pound of other animals. When it comes to shrimp, the ratio is even more astronomical: For every pound of shrimp, four or more pounds of unwanted animals die. [1] Bycatch mortality can decrease the sustainability of fisheries and the net benefits provided by the fisheries in several ways. It can be stopped at no cost, bycatch would be neither a complex nor contentious fishery management problem, and bycatch would simply be eliminated. It is a contentious issue, in part, because actions to reduce bycatch mortality typically change the distribution of the net benefits from the fisheries.[2]

Bycatch mitigation

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.

BRDs allow the escape of commercially important species of finfish. Federally-approved BRDs reduce finfish bycatch by approximately 30%, and the numbers of Weakfish and Spanish Mackerel caught in the South Atlantic fishery by 40%.³ Despite recent advancements in bycatch reduction, recent information suggests BRDs may not be as effective in reducing bycatch as previously thought.⁵ A recent analysis of bycatch from commercial fishers using Bycatch Reduction Devices (BRDs) in the Rock Shrimp fishery off the east coast of Florida identified 37 species of Crustaceans, 166 fish species and 29 other invertebrate species, all of which were not excluded by the devices.³

Between 1978 and 1984, the National Marine Fisheries Service (NMFS) began developing Turtle excluder device (TEDs). A TED is a grid-like structure which directs turtles, and other large animals, out of trawl nets through a hole above the grid. All U.S. shrimp trawlers—and all foreign fleets selling shrimp in the U.S—are supposed to outfit their nets with the trap-door TEDs. However, not every nation enforces TED use with equal vigour.

TEDs have been largely successful in reducing sea turtle bycatch in the US shrimp trawl fishery.¹²³ Crowder 2001). However, they are not completely effective, and some turtles do not escape capture^{3 11} To be certified by the National Marine Fisheries Service, a TED design must be 97% effective. In heavily trawled areas, the same sea turtle may pass repeatedly through TEDs.¹¹ Recent studies indicate recapture rates of twenty percent or more, but it is not clear how many turtles survive the escape process.¹¹

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."

Longline fishing is controversial in some areas because of by-catch. Methods to mitigate such incidental mortality have been developed and successfully implemented in some fisheries. These include the use of weights to ensure the lines sink quickly, the deployment of streamer lines to scare birds away from the baited hooks as they are deployed, setting lines only at night with ship lighting kept low (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 and the controversy continues. In March 2006, the Hawaii longline swordfish fishing season was closed due to excessive loggerhead sea turtle by-catch after being open only a few months, despite using modified circle hooks which attempt to reduce by-catch.

In addition to efforts to reduce the amount of bycatch caught in nets, some fisheries are starting to implement programs to effectively utilize bycatch species, rather than throwing the fish back into the ocean. One such use of bycatch is the formulation of fish hydrolysate that can be used as a soil amendment in organic agriculture.

See also

• Discards
• Cetacean bycatch
• List of environmental issues
• Incidental mortality
• Fish hydrolysate

Notes

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.
• Demaster, DJ, Fowler, CW, Perry, SL, and ME Richlen (2001). Predation and competition: the impact of fisheries on marine mammal populations over the next one hundred years. Journal of Mammology. 82: 641-651.
• Epperly, S; Avens, L; Garrison, L; Henwood, T; Hoggard, W; Mitchell, J; Nance, J; Poffenberger, J; Sasso, C; Scott-Denton, E and Young, C (2002) Analysis of Sea Turtle Bycatch in the Commercial Shrimp Fisheries of Southeast US Waters and the Gulf of Mexico. NOAA Technical Memorandum NMFS-SEFSC-490.
• Gulf of Mexico Fishery Management Council (GMFMC) (2006) Scoping Document for Amendment 15 to the Shrimp FMP
• GMFMC(2005) Final Amendment Number 13 to the Fishery Management Plan for the Shrimp Fishery of the Gulf of Mexico US Waters with Environmental Assessment Regulatory Impact Review, and Regulatory Flexibility Act Analysis.
• Hall M A (1996) On bycatches. Reviews in Fish Biology and Fisheries vol. 6 (3) pp 319 - 352 (1996)
• Hall, M; D.L. Alverson, DL and Metuzals, KI (2000) By-Catch: Problems and Solutions. Marine Pollution Bulletin. Vol. 41, Nos. 1-6: 204-219
• Morgan, LE and Chuenpagdee, R (2003) Shifting Gears. Addressing the Collateral Impacts of Fishing Methods in U.S. Waters.
• OECD (1997) Towards sustainable fisheries: economic aspects of the management of living marine resources. OECD Paris.
• Read, AJ, Drinker, P, and S Northridge (2006). Bycatch of marine mammals in the U.S. and Global Fisheries. Conservation Biology. 20(1): 163-169.
• 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.
• Southeast Data, Assessment, and Review (SEDAR) (2005) Stock Assessment Report of SEDAR 7 Gulf of Mexico Red Snapper: Assessment Summary Report.

External links

• 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
• U.S. Shrimp (South Atlantic and Gulf of Mexico)

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