Editing Bycatch

{{Short description|Fish or other marine species caught unintentionally}}
[[File:Carcharhinus isodon in net.JPG|alt=Shark entangled in a net on board a fishing vessel|thumb|A [[finetooth shark]] (''Carcharhinus isodon'') caught as bycatch by a fishing vessel]]
'''Bycatch''' (or '''by-catch'''), in the [[fishing industry]], is a [[fish]] 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 [[Juvenile (organism)|juvenile]]s of the target species. The term "bycatch" is also sometimes used for untargeted catch in other forms of animal harvesting or collecting. Non-[[marine life|marine]] species ([[freshwater fish]] not [[saltwater fish]]) that are caught (either intentionally or unintentionally) but regarded as generally "undesirable" are referred to as [[rough fish]] (mainly US) or [[coarse fishing|coarse fish]] (mainly UK).

In 1997, the [[OECD|Organisation for Economic Co-operation and Development]] (OECD) defined bycatch as "total fishing [[Mortality rate|mortality]], excluding that accounted directly by the retained catch of target species".<ref>OECD (1997) Towards sustainable fisheries: economic aspects of the management of living marine resources. OECD Paris.</ref> Bycatch contributes to fishery decline and is a mechanism of [[overfishing]] for unintentional catch.<ref>C. Michael Hogan. 2010. [https://editors.eol.org/eoearth/wiki/Overfishing ''Overfishing''. Encyclopedia of Earth. National Council for Science and the Environment]. eds. Sidney Draggan and C. Cleveland. Washington DC.</ref>

The average annual bycatch rate of [[pinniped]]s and [[cetacea]]ns in the US from 1990 to 1999 was estimated at 6215 animals with a [[standard error]] of 448.<ref>{{cite journal|last1=Read|first1=Andrew J.|last2=Drinker|first2=Phebe|last3=Northridge|first3=Simon|title=Bycatch of Marine Mammals in U.S. and Global Fisheries|journal=Conservation Biology|date=February 2006|volume=20|issue=1|pages=163–169|doi=10.1111/j.1523-1739.2006.00338.x|pmid=16909669|bibcode=2006ConBi..20..163R |s2cid=157350 }}</ref>

Bycatch issues originated with the "mortality of dolphins in tuna nets in the 1960s".<ref name=Hall/>

There are at least four different ways the word "bycatch" is used in fisheries:<ref>{{cite book|author1=Alverson D L |author2=Freeberg M K |author3=Murawski S A |author4=Pope J G |year=1994|title=A global assessment of fisheries bycatch and discards|publisher=FAO|location=Rome}}</ref>
* Catch which is retained and sold but which is not the target species for the fishery {{Citation needed|date=October 2023}}
* Species/sizes/sexes of fish which [[fisherman|fishers]] discard<ref>A definition used particularly in the northeast and western [[Pacific]] and in US legislation</ref>
* Non-target fish, whether retained and sold or discarded<ref>{{cite journal|last=Hall |first=M A |year=1996|title=On bycatches|journal=Reviews in Fish Biology and Fisheries |volume=6
|issue=3|pages=319–352 |doi=10.1007/BF00122585|bibcode=1996RFBF....6..319H |s2cid=25760363 }}</ref>
* Unwanted [[invertebrate]] species, such as [[echinoderm]]s and non-commercial [[crustacean]]s, and various vulnerable species groups, including seabirds, sea turtles, marine mammals and elasmobranchs (sharks and their relatives).<ref>{{Cite journal |last1=Blom |first1=Wilma |last2=Webber |first2=Richard |last3=Shultz |first3=Thomas |date=2009-06-01 |title=Invertebrate bycatch from bottom trawls in the New Zealand EEZ |url=https://tuhinga.arphahub.com/article/34177/ |journal=Tuhinga |language=en |volume=20 |pages=33–40 |doi=10.3897/tuhinga.20.e34177 |doi-access=free |issn=2253-5861}}</ref>

Additionally, the term "deliberate bycatch" is used to refer to bycatch as a source of [[illegal wildlife trade]] (IWT) in several areas throughout the world.<ref>{{Cite journal |last1=Ermolin |first1=Ilya |last2=Svolkinas |first2=Linas |date=January 2018 |title=Assessment of the sturgeon catches and seal bycatches in an IUU fishery in the Caspian Sea |journal=[[Marine Policy]] |volume=87 |issue=87 |pages=284–290 |doi=10.1016/j.marpol.2017.09.022 |url=https://www.researchgate.net/publication/321289096 }}</ref>

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.<ref>{{cite journal|last1=Manlik|first1=Oliver|last2=Lacy|first2=Robert C.|last3=Sherwin|first3=William B.|last4=Finn|first4=Hugh|last5=Loneragan|first5=Neil |last6=Allen|first6=Simon C.|title=A stochastic model for estimating sustainable limits to wildlife mortality in a changing world|journal=Conservation Biology|date=2022|volume=36 |issue=4 |pages=e13897|doi=10.1111/cobi.13897|pmid=35122329|pmc=9542519 |bibcode=2022ConBi..36E3897M }}</ref>

== 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.<ref>{{Cite journal |doi = 10.7287/peerj.preprints.120v1|title = By-catch in a recreational fishery: An unmonitored source of mortality|last1 = McCallum|first1 = Malcolm L.|last2 = Worley|first2 = Gina M.|last3 = Safi|first3 = Barroq|last4 = Dickens|first4 = Kris|last5 = Jones|first5 = Jason|last6 = McCallum|first6 = Jamie L.|journal=PeerJ Preprints|doi-access = free}}</ref>

===Shrimp trawling===
[[File:Trawer Hauling Nets.jpg|thumb|right|Double-rigged shrimp [[fishing trawler|trawler]] hauling in [[Fishing net|nets]]|alt=Photo of boat moving forward at sea. On each side, the boat has one pole pointing away from boat with nets attached]] 
[[File:Shrimp bycatch.jpg|thumb|right|[[Shrimp]] bycatch|alt=Photo of hundreds of dead fish lying on ship deck]]

The highest rates of [[incidental catch]] of non-target species are associated with tropical [[shrimp]] [[trawling]]. In 1997, the [[FAO|Food and Agriculture Organization of the United Nations]] (FAO) documented the estimated bycatch and [[Discards|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.<ref>{{cite book|last=Clucas |first=Ivor|year=1997|url=http://www.fao.org/docrep/W6602E/w6602E09.htm|title=Discards and bycatch in shrimp trawl fisheries
|publisher=[[FAO]] Fisheries Circular|issue= 928 FIIU/C928}}</ref>

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).<ref name=Hall>{{cite journal|last1=Hall |first1=M |last2=Alverson |first2=DL |last3=Metuzals |first3=KI|year=2000
|title=By-catch: problems and solutions|journal=Marine Pollution Bulletin|volume=41|issue=1–6|pages=204–219 |doi=10.1016/S0025-326X(00)00111-9|bibcode=2000MarPB..41..204H }}</ref>

[[Trawling|Trawl nets]] in general, and shrimp trawls in particular, have been identified as sources of mortality for [[cetacea]]n and [[finfish]] species.<ref name="SAFMC">SAFMC (2004){{Full citation needed|date=June 2021}}</ref> When bycatch is discarded (returned to the sea), it is often dead or dying.<ref>{{cite book|last1=Morgan |first1=LE |last2=Chuenpagdee |first2=R
|year=2003|title=Shifting Gears. Addressing the Collateral Impacts of Fishing Methods in U.S. Waters}}</ref>

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&nbsp;kg of bycatch. In tropical inshore waters the bycatch usually consists of small fish. The shrimps are frozen and stored on board; the bycatch is discarded.<ref>{{cite book|editor=Clucas, I. |editor2=Teutscher, F. |title=FAO/DFID Expert Consultation on Bycatch Utilization in Tropical Fisheries. Beijing (China), 21–28 September 1998|year=1999|publisher=University of Greenwich, NRI|isbn=978-0-85954-504-4|page=333}}</ref>

Recent sampling in the South Atlantic [[Sicyonia brevirostris|rock shrimp]] fishery found 166 species of finfish, 37 [[crustacean]] species, and 29 other species of [[invertebrate]] among the bycatch in the trawls.<ref name="SAFMC"/> 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, [[Crangon crangon|brown shrimp]], longspine swimming crabs, and other bycatch made up the rest.<ref name="SAFMC"/>

Despite the use of [[bycatch reduction device]]s, the shrimp fishery in the Gulf of Mexico removes about 25–45 million [[Lutjanus|red snapper]] annually as bycatch, nearly one-half the amount taken in recreational and commercial snapper fisheries.<ref name="GMFMC (2006)"/><ref>{{cite book|publisher=Southeast Data, Assessment, and Review (SEDAR) Stock Assessment Report of SEDAR
|issue=7|year=2005|url=http://www.sefsc.noaa.gov/sedar/download/S7SAR_FINALreduce.pdf?id=DOCUMENT|title=Gulf of Mexico Red Snapper: Assessment Summary Report}}</ref>

===Cetacean===
{{main|Cetacean bycatch}}
[[File:Fraser s group.jpg.jpeg|thumb|left|Group of [[Cetacean bycatch#Spinner and Fraser's dolphins|Fraser's dolphins]]]]
[[Cetacean]]s, such as [[dolphin]]s, [[porpoise]]s, and [[whale]]s, can be seriously affected by entanglement in [[fishing net]]s and [[fishing line|lines]], or direct capture by [[Fish hook|hooks]] or in [[Trawling|trawl nets]]. Cetacean bycatch is increasing in intensity and frequency.<ref name="Demaster (2001)">{{cite journal
|last1=Demaster |first1=DJ |last2=Fowler |first2=CW |last3=Perry |first3=SL |first4=ME |last4=Richlen 
|year=2001
|title=Predation and competition: the impact of fisheries on marine mammal populations over the next one hundred years
|journal=Journal of Mammalogy
|volume=82
|issue=3
|pages=641–651 |doi=10.1644/1545-1542(2001)082<0641:PACTIO>2.0.CO;2
|doi-access=free }}</ref> In some fisheries, cetaceans are captured as bycatch but then retained because of their value as [[Whale meat|food]] or [[Bait fish|bait]].<ref name="Read (2006)">{{cite journal |vauthors=Read AJ, Drinker P, Northridge S |year=2006 |title=Bycatch of marine mammals in the U.S. and global fisheries |journal=[[Conservation Biology (journal)|Conservation Biology]] |volume=20 |issue=1 |pages=163–169 |pmid=16909669 |doi=10.1111/j.1523-1739.2006.00338.x|bibcode=2006ConBi..20..163R |s2cid=157350 }}</ref> In this fashion, cetaceans can become a target of fisheries.

[[File:Entangled porpoise.jpg|right|thumb|A [[Dall's porpoise]] caught in a fishing net]]
One example of bycatch is dolphins caught in [[tuna]] nets. As dolphins are [[mammal]]s and do not have [[gill]]s, they may drown while stuck in nets underwater. This bycatch issue has been one of the reasons of the growing [[ecolabel]]ling 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 [[Dolphin#Social behavior|pod]] of dolphins, but relied on other methods to spot tuna schools.{{citation needed|date=April 2009}}
The bycatch of the [[Caspian seal]] may be recognized as one of the biggest entanglements of pinnipeds as bycatch in the world <ref>{{cite journal |doi=10.1371/journal.pone.0067074|pmid=23840590|pmc=3694144|title=Assessment of Caspian Seal By-Catch in an Illegal Fishery Using an Interview-Based Approach|journal=PLOS ONE|volume=8|issue=6|pages=e67074|year=2013|last1=Dmitrieva|first1=Lilia|last2=Kondakov|first2=Andrey A.|last3=Oleynikov|first3=Eugeny|last4=Kydyrmanov|first4=Aidyn|last5=Karamendin|first5=Kobey|last6=Kasimbekov|first6=Yesbol|last7=Baimukanov|first7=Mirgaliy|last8=Wilson|first8=Susan|last9=Goodman|first9=Simon J.|bibcode=2013PLoSO...867074D|doi-access=free}}</ref><ref>{{cite journal |doi=10.1016/j.marpol.2017.09.022|title=Assessment of the sturgeon catches and seal bycatches in an IUU fishery in the Caspian Sea|journal=Marine Policy|volume=87|pages=284–290|year=2018|last1=Ermolin|first1=Ilya|last2=Svolkinas|first2=Linas|url=http://eprints.whiterose.ac.uk/124584/5/Assessment%20of%20IUU%20catches%20after%20revision.pdf}}</ref>

===Albatross===
{{see also|Longline fishing}}
[[File:Albatross hook.jpg|thumb|left|[[Black-browed albatross]] hooked on a long-line|alt=Photo of bird struggling to fly away]]

Of the 22 [[albatross]] species recognised by IUCN on their [[IUCN Red List|Red List]], 15 are [[Threatened species|threatened with extinction]], six species are considered as [[Near-threatened species|Near Threatened]], and only one of [[Least-concern species|Least Concern]].<ref name=":1">{{Cite web |title=BirdLife Data Zone |url=http://datazone.birdlife.org/species/results?cmn=albatross&cty=0&fam=0&gen=0&kw=&reg=0&spc=&thrlev1=&thrlev2=&so=rl |access-date=2022-12-28 |website=datazone.birdlife.org}}</ref> Two species, the [[Tristan albatross]] and the [[waved albatross]], are considered as [[Critically Endangered]].<ref name=":1" /> One of the main threats is commercial [[longline fishing]],<ref>{{cite journal |author=Brothers NP |year=1991 |title=Albatross mortality and associated bait loss in the Japanese longline fishery in the southern ocean |journal=Biological Conservation |volume=55 |issue=3 |pages=255–268 |doi=10.1016/0006-3207(91)90031-4|bibcode=1991BCons..55..255B }}</ref> because albatrosses and other [[seabird]]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 [[Illegal, unreported and unregulated fishing|pirate fisheries]] exacerbate the problem.

A research study examined the impact of illegal [[longline fishing]] vessels on albatrosses, by using [[environmental criminology]] as a guiding theoretical framework.<ref name=":2">{{Cite journal |last1=Petrossian |first1=Gohar A. |last2=Pires |first2=Stephen F. |last3=Sosnowski |first3=Monique |last4=Venu |first4=Prabha |last5=Olah |first5=George |date=2022 |title=Threats of Longline Fishing to Global Albatross Diversity |journal=Animals |language=en |volume=12 |issue=7 |page=887 |doi=10.3390/ani12070887 |pmid=35405876 |pmc=8997039 |issn=2076-2615|doi-access=free }} {{Creative Commons text attribution notice|cc=by4|from this source=yes}}</ref> The results indicated that potentially illegal longline fishing activities are highly concentrated in areas of illegally-caught fish species, and the risk to bycatch albatrosses is significantly higher in areas where these illegal longline fishing vessels operate.<ref name=":2" /> These findings provide strong grounding that illegal longline fishing poses a particularly serious threat to the survival of [[seabird]]s.
{{clear}}

===Sea turtles===
[[File:Loggerhead Sea Turtle.jpg|thumb|left|[[Loggerhead sea turtle]]|alt=Sea turtle swimming near a diverse group of fish.]]
[[Sea turtle]]s, already critically endangered, have been killed in large numbers in shrimp trawl nets. Estimates indicate that thousands of [[Kemp's ridley sea turtle|Kemp's ridley]], [[loggerhead sea turtle|loggerhead]], [[Green sea turtle|green]], and [[leatherback sea turtle]]s are caught in shrimp trawl fisheries in the [[Gulf of Mexico]] and the US [[Atlantic]] annually<ref name="Epperly">{{Cite journal |last1=Epperly |first1=S |last2=Avens |first2=L |last3=Garrison |first3=L |last4=Henwood |first4=T |last5=Hoggard |first5=W |last6=Mitchell |first6=J |last7=Nance |first7=J |last8=Poffenberger |first8=J |last9=Sasso |first9=C |last10=Scott-Denton |first10=E and |last11=Young |first11=C |year=2002 |access-date=20 December 2009 |url=http://www.sefsc.noaa.gov/PDFdocs/TM_490_Epperly_etal.pdf |title=Analysis of Sea Turtle Bycatch in the Commercial Shrimp Fisheries of Southeast US Waters and the Gulf of Mexico |journal=NOAA Technical Memorandum NMFS-SEFSC-490 |archive-url=https://web.archive.org/web/20090509022328/http://www.sefsc.noaa.gov/PDFdocs/TM_490_Epperly_etal.pdf |archive-date=2009-05-09 }}</ref> 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".<ref>{{cite journal |doi=10.1017/S0030605310001286 | volume=45 | title=Sea turtle bycatch and consumption in Egypt threatens Mediterranean turtle populations | year=2011 | journal=Oryx | pages=143–149 | last1 = Nada | first1 = Mohamed | last2 = Casale | first2 = Paolo| doi-access=free }}</ref>

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.<ref name="Epperly"/>
{{clear}}

===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 [[Seine fishing|purse seine]] 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]], [[longline fishing|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.<ref name="seafoodwatch.org">{{cite web|url=https://www.seafoodwatch.org/ocean-issues/wild-seafood/bycatch|title=Effects of Bycatch from Fishing for Wild Seafood from the Seafood Watch Program at the Monterey Bay Aquarium|website=www.seafoodwatch.org}}</ref> 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.<ref>{{cite web|url=https://www.worldwildlife.org/threats/bycatch|title=Bycatch - Threats|website=World Wildlife Fund}}</ref> 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.<ref name="seafoodwatch.org"/>

==Mitigation==
[[File:Turtle excluder device 2.png|thumb|right|A [[turtle excluder device]]|alt=]]
Concern about bycatch has led fishers and scientists to seek ways of reducing unwanted catch.<ref>[http://www.ecosafetuna.org/about/campaign-eco-safe-tuna.html Campaign for Eco-Safe Tuna] Retrieved 2.21.2012</ref> 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 net|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 device]]s (BRDs) and the [[Nordmore grate]] are net modifications that help fish escape from shrimp nets.

===Bycatch reduction devices===
BRDs allow many commercial finfish species to escape. The US government has approved BRDs that reduce finfish bycatch by 30%. [[Spanish mackerel]] and [[weakfish]] bycatch in the South Atlantic was reduced by 40%.<ref name="SAFMC"/> However, recent surveys suggest BRDs may be less effective than previously thought.<ref name="GMFMC (2006)">Gulf of Mexico Fishery Management Council (GMFMC) (2006) [http://www.gulfcouncil.org/Beta/GMFMCWeb/downloads/Shrimp%20Amend%2015%20Scoping%20106.pdf#search='shrimp%20amendment%2015' ''Scoping Document for Amendment 15 to the Shrimp FMP''] {{Webarchive|url=https://web.archive.org/web/20081217160414/http://www.gulfcouncil.org/Beta/GMFMCWeb/downloads/Shrimp%20Amend%2015%20Scoping%20106.pdf#search='shrimp%20amendment%2015' |date=2008-12-17 }}</ref> A rock shrimp fishery off Florida found the devices failed to exclude 166 species of fish, 37 crustacean species, and 29 species of other invertebrates.<ref name="SAFMC"/>

A pulsed electric field-based [[Shark#Conservation|shark]] and [[Batoidea#Conservation|ray]] bycatch mitigation device, SharkGuard, was reported by 2022 study to have reduced bycatch of blue shark by 91% and of stingrays by 71% with commercial fishing gear in a French longline tuna fishery in the Mediterranean.<ref>{{cite news |title=New gadget could reduce shark bycatch by 90% |url=https://www.theguardian.com/environment/2022/nov/21/new-gadget-could-reduce-shark-bycatch-by-90 |access-date=18 December 2022 |work=The Guardian |date=21 November 2022 |language=en}}</ref><ref>{{cite journal |last1=Doherty |first1=Philip D. |last2=Enever |first2=Robert |last3=Omeyer |first3=Lucy C. M. |last4=Tivenan |first4=Lydia |last5=Course |first5=Grant |last6=Pasco |first6=Guy |last7=Thomas |first7=David |last8=Sullivan |first8=Ben |last9=Kibel |first9=Ben |last10=Kibel |first10=Pete |last11=Godley |first11=Brendan J. |title=Efficacy of a novel shark bycatch mitigation device in a tuna longline fishery |journal=Current Biology |date=21 November 2022 |volume=32 |issue=22 |pages=R1260–R1261 |doi=10.1016/j.cub.2022.09.003 |pmid=36413965 |language=English |issn=0960-9822|doi-access=free|bibcode=2022CBio...32R1260D |hdl=10871/132022 |hdl-access=free }}</ref>

===Turtle excluder devices===
In 1978, the [[National Marine Fisheries Service]] (NMFS) started to develop [[turtle excluder device]]s (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.<ref name="SAFMC"/><ref name="GMFMC (2005)">{{cite web| year=2005|url=http://www.gulfcouncil.org/Beta/GMFMCWeb/downloads/Shrimp%20Amend%2013%20Final%20805.pdf|title=Final Amendment Number 13 to the Fishery Management Plan for the Shrimp Fishery of the Gulf of Mexico |work= US Waters with Environmental Assessment Regulatory Impact Review, and Regulatory Flexibility Act Analysis}}</ref><ref>Crowder, 2001{{citation needed|date=July 2013}}</ref> However, they are not completely effective, and some turtles are still captured.<ref name="SAFMC"/><ref name="Epperly"/> NMFS certifies TED designs if they are 97% effective. In heavily trawled areas, the same sea turtle may pass repeatedly through TEDs.<ref name="Epperly"/> Recent studies indicate recapture rates of 20% or more, but it is not clear how many turtles survive the escape process.<ref name="Epperly"/>

===Conservation engineering of trawl nets===
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".

[[File:Seabirds longlinersm.jpg|thumb|left|[[Seabird]]s chase longline [[fishing vessel]]|alt=Photo of hundreds of seabirds on water surface around boat]]
[[Longline fishing]] is controversial in some areas because of bycatch. 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)
* not discharging offal while setting lines.

However, gear modifications do not eliminate bycatch of many species. In March 2006, the [[Hawaii|Hawai{{okina}}i]] longline swordfish fishing season was closed due to excessive [[loggerhead sea turtle]] bycatch after being open only a few months, despite using modified [[circle hook]]s.

[[File:Bycatch - tori lines (streamer lines).svg|thumb|One of the mitigation methods is using streamer lines (in orange).]]

===No discards policy===
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.<ref name=":0">{{Cite journal |last1=Gullestad |first1=P. |last2=Blom |first2=G. |last3=Bakke |first3=G. |last4=Bogstad |first4=B. |date=2015-04-01 |title=The "Discard Ban Package": Experiences in efforts to improve the exploitation patterns in Norwegian fisheries |url=https://www.sciencedirect.com/science/article/pii/S0308597X14002589 |journal=Marine Policy |language=en |volume=54 |pages=1–9 |doi=10.1016/j.marpol.2014.09.025 |issn=0308-597X|hdl=11250/273853 |hdl-access=free }}</ref> 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.<ref name=Hall/><ref name=":0" />

===Seabirds===
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 [[Demersal fish|groundfish]] longline fisheries, as the deaths of seabirds declined by about 70% after the deployment of these lines.<ref name="seafoodwatch.org"/>

==Alternative to discarding==
Some fisheries retain bycatch, rather than throwing the fish back into the ocean. Sometimes bycatch is sorted and sold as food,<ref>Engelhardt, Elizabeth, [http://southernspaces.org/2011/oyster-any-other-name "An Oyster by Any Other Name"], ''Southern Spaces'', 18 April 2011</ref> 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]]. In [[Southeast Asia]] 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]]) 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 trap]]s or [[flight interception trap]]s for either financial, controlling or scientific purposes (where the bycatch may either be small vertebrates<ref>{{cite journal | year = 1999 | title = Bycatch, ethics and pitfall traps | journal = Journal of Insect Conservation | volume = 3 | issue = 1| pages = 1–3 | doi=10.1023/A:1017191920328| s2cid = 264021128 }}</ref> or untargeted insects) and control of introduced vertebrates which have become pest species like the [[muskrat]] in Europe (where the bycatch in [[trapping|traps]] may be [[European mink]]s<ref>Kranz A, Polednik L and Gotea V (2001) [http://php.scripts.psu.edu/users/v/x/vxg901/publ/ddiannals2001_124-129.pdf Conservation of the European Mink (''Mustella lutreila'') in the Danube Delta] {{Webarchive|url=https://web.archive.org/web/20110929032133/http://php.scripts.psu.edu/users/v/x/vxg901/publ/ddiannals2001_124-129.pdf# |date=2011-09-29 }} Background information and project plan. ''Scientific Annals of the Danube Delta Institute for Research and Development'', Tulcea, 2000–2001.</ref> or [[waterfowl]]).

== See also ==
{{div col|colwidth=20em}}
* [[Community-supported fishery#Environmental stewardship|Environmental stewardship]]
* [[Discards]]
* [[Cetacean bycatch]]
* [[List of environmental issues]]
* [[Shrimp turtle case]]
* [[Ghost net]]
{{div col end}}

==References==
{{reflist|32em}}

==Further reading==
{{refbegin|2}}
* FAO (2009) ''Technical Guidelines for Responsible Fisheries'', Number 1: Fishing operations, supplement 2 [http://www.ecologyandsociety.org/vol14/iss2/art32/figure6.html Best practices to reduce incidental catch of seabirds in capture fisheries] Rome. {{ISBN|978-92-5-106423-8}}.
* FAO (1997) ''A STUDY OF THE OPTIONS FOR UTILIZATION OF BYCATCH AND DISCARDS FROM MARINE CAPTURE FISHERIES'' [http://www.fao.org/docrep/w6602e/w6602E00.htm A STUDY OF THE OPTIONS FOR UTILIZATION...]
* Karp WA, Desfosse LL and Brooke SG (2011) [http://www.nmfs.noaa.gov/by_catch/bycatch_nationalreport.htm U.S. National Bycatch Report] {{Webarchive|url=https://web.archive.org/web/20180111230505/http://www.nmfs.noaa.gov/by_catch/bycatch_nationalreport.htm |date=2018-01-11 }} National Marine Fisheries Service, NOAA Technical Memo NMFS-F/SPO-117E.
* SAFMC (1998) [https://web.archive.org/web/20080524170342/http://www.safmc.net/Default.aspx?tabid=80 ''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.
* [https://web.archive.org/web/20091108113942/http://www.blueoceaninstitute.org/seafood/species/157.html U.S. Shrimp (South Atlantic and Gulf of Mexico)] – Blue Ocean Institute. Retrieved 22 March 2008.
{{refend}}

==External links==
*[https://www.dailymotion.com/video/xuoria Mitigating Adverse Ecological impacts of open oceanfisheries – European project MADE (28 minute film)]
*[https://web.archive.org/web/20110213102350/http://ocean.si.edu/ocean-portal-generated-tags/bycatch Bycatch – Smithsonian Ocean Portal]
*[https://www.bmis-bycatch.org Bycatch Management Information System – mitigation techniques, species ID & safe handling, regulations, curated literature]
*[https://web.archive.org/web/20130702080537/http://www.lenfestocean.org/sites/default/files/lenfest_rfmo_rs_final_aa.pdf Lenfest Ocean Program publication on regional governance of bycatch in tuna fisheries]
*[https://web.archive.org/web/20100923231245/http://bycatch.env.duke.edu/ Project GLOBAL: Global Bycatch Assessment of Long-Lived Species project]
*[https://oceana.org/our-campaigns/bycatch/campaign Oceana facts about bycatch/dirty fishing]
*[https://www.fao.org/3/w6602e/w6602e00.htm FAO document on bycatch and discard]
*[https://web.archive.org/web/20060619193118/http://oceans.greenpeace.org/en/our-oceans/bycatch Greenpeace facts about bycatch]
*[http://www.akmarine.org Alaska Marine Conservation Council]
* Johnson, Douglas H; Shaffer, Terry L and Gould, Patrick J (1990) [https://web.archive.org/web/20100529211656/http://www.npwrc.usgs.gov/resource/birds/icatch/index.htm ''Incidental Catch of Marine Birds in the North Pacific High Seas Driftnet Fisheries''] [[U.S. Geological Survey]].
* Valdemarsen, John W [https://web.archive.org/web/20070718075239/http://www.oceansatlas.org/world_fisheries_and_aquaculture/html/issues/ecosys/selectgear/incidental_catch.htm ''Incidental catch of seabirds in longline fisheries''] UN Atlas of the Oceans: Fishery Technology Service.

{{fishery science topics|expanded=management}}
{{Fishing industry topics}}

{{Authority control}}

[[Category:Environmental impact of fishing]]
[[Category:Bird mortality]]