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The '''signal crayfish''' ('''''Pacifastacus leniusculus''''') is a [[North America]]n species of [[crayfish]]. It was introduced to Europe in the 1960s to supplement the North European ''[[Astacus astacus]]'' fisheries, which were being damaged by [[crayfish plague]], but the imports turned out to be a carrier of that disease. The signal crayfish is now considered an [[invasive species]] across Europe, Japan, and California, ousting native species there.
==Description and ecology==
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==Native range==
The signal crayfish is native to [[North America]] west of the [[Rocky Mountains]], including the [[Provinces and territories of Canada|Canadian province]] of [[British Columbia]], and the [[U.S. state]]s of [[Washington (state)|Washington]], [[Oregon]], and [[Idaho]].<ref name="Fetzner">{{cite web|author=James W. Fetzner Jr.|date=January 14, 2008|title=''Pacifastacus (Pacifastacus) leniusculus leniusculus'' (Dana, 1852). Signal crayfish |work=Crayfish Taxon Browser|publisher=[[Carnegie Museum of Natural History]]|access-date=August 8, 2010|url=http://iz.carnegiemnh.org/crayfish/NewAstacidea/species.asp?g=Pacifastacus&s=leniusculus&ssp=leniusculus}}</ref> It was introduced to [[California]] in 1912 into the [[San Lorenzo River]] watershed and from there rapidly spread throughout the state.<ref>{{cite news|title=Fighting the Bay Area Invasion of Signal Crayfish|author=Joe Eaton|newspaper=Berkeley Daily Planet|date=May 17, 2005|url=http://www.berkeleydailyplanet.com/issue/2005-05-17/article/21428?headline=Fighting-the-Bay-Area-Invasion-of-Signal-Crayfish-By-JOE-EATON-Special-to-the-Planet|access-date=December 18, 2019}}</ref> The only native crayfish remaining in California (aside from ''Pacifastacus leniusculus klamathensis,'' a subspecies of signal crayfish believed to be native to the Klamath River in Northern California) is the [[Shasta crayfish]], of [[Shasta County, California]] (''Pacifastacus fortis''), where efforts are being made to create a barrier to signal crayfish invasion.<ref>{{cite web|title=PG&E Joins Forces to Save the Endangered Shasta Crayfish|publisher=PG&E|url=http://www.pge.com/about/environment/pge/stewardship/crayfish/|access-date=September 4, 2011|archive-url=https://web.archive.org/web/20111019103453/http://www.pge.com/about/environment/pge/stewardship/crayfish/|archive-date=October 19, 2011|url-status=dead}}</ref> Within North America, it has also been introduced to [[Nevada]], and the populations in [[Utah]] may be the result of introductions.<ref name="Fetzner"/> It has also been found in Alaska, specifically Kodiak Island, in the Buskin River and Buskin Lake. It is listed as a species of [[least concern]] on the [[IUCN Red List]].<ref name=IUCN>{{cite
==Introduction into Europe==
[[File:Pacifastacus leniusculus 01 by-dpc.jpg|thumb|left|A signal crayfish in Spain]]
From 1907, [[crayfish plague]], an infectious disease caused by the [[water mould]] ''Aphanomyces astaci'', damaged stocks of the native European crayfish ''[[Astacus astacus]]''. Since the signal crayfish occupied a similar [[ecological niche]] in its native range, it was imported in the 1960s to [[Sweden]] and [[Finland]] to allow recreational and commercial crayfish capture.<ref name="Nobanis">{{cite web|author1=Trond Taugbøl|author2=Stein I. Johnsen|name-list-style=amp|year=2006|title=Invasive Alien Species Fact Sheet – ''Pacifastacus leniusculus''|work=Online Database of the North European and Baltic Network on Invasive Alien Species|publisher=NOBANIS – European Network on Invasive Species|url=http://www.nobanis.org/files/factsheets/Pacifastacus_leniusculus.pdf|access-date=August 28, 2010}}</ref> At the time, the signal crayfish was not recognized as a [[Asymptomatic carrier|carrier]] of the crayfish plague.<ref name="Nobanis"/> All American species carry the infection, but it is only lethal to individuals that are already stressed; to European species, the infection is rapidly fatal.<ref name="Summer">{{cite book|editor=Norman Maclean|year=2010|title=Silent Summer: The State of Wildlife in Britain and Ireland|publisher=[[Cambridge University Press]]|chapter=Other invertebrates|pages=556–575|author1=[[Richard Chadd]]|author2=Brian Eversham|isbn=9781139788694}}</ref>
The signal crayfish is now the most widespread alien crayfish in Europe, occurring in 25 countries, from [[Finland]] to [[Great Britain]] and from [[Spain]] to [[Greece]].<ref name="Nobanis"/><ref>{{cite journal|author=Silva, S.|author2=Outón, P.|author3=Nachón, D. J.|author4=Gómez-Sande, P.|author5=Sánchez-Hernández, J.|author6=Vieira-Lanero, R.|author7=Cobo, F.|year=2017|title=New data on the introduction of the invasive signal crayfish ''Pacifastacus leniusculus'' (Dana, 1852) (Crustacea, Decapoda) and ectosymbiont branchiobdellidans (Annelida, Clitellata) in NW Iberian Peninsula|journal=Nova Acta Científica Compostelana (Bioloxía)|volume=24|pages=63–68|issn=2340-0021|url=http://www.usc.es/revistas/index.php/nacc/article/view/3970/4199}}</ref> It was first introduced to Great Britain in 1976,<ref name="Brit-Eco-Soc">{{ cite web | url=http://www.britishecologicalsociety.org/crayfish-trapping-fails-to-control-invasive-species/ | title=Crayfish 'trapping' fails to control invasive species | date=13 October 2020 }}</ref><ref name="Daniel-Chadwick-et-al-2020">{{ Cite journal
In both Sweden and Finland (where crayfish are eaten), the catch of signal crayfish exceeds that of ''A. astacus'' (European/noble crayfish). The former is sold at roughly half the price compared to the latter.<ref>{{cite web|url=https://www.fws.gov/fisheries/ans/erss/highrisk/Pacifastacus-leniusculus-ERSS-revision-June2015.pdf|title=Signal Crayfish (Pacifastacus leniusculus) Ecological Risk Screening Summary|publisher=U.S. Fish and Wildlife Service|date=February 2011}}</ref>
In Europe, the signal crayfish is included since 2016 in the list of Invasive Alien Species of Union concern (the Union list).<ref>{{Cite web|title=List of Invasive Alien Species of Union concern - Environment - European Commission|url=https://ec.europa.eu/environment/nature/invasivealien/list/index_en.htm|access-date=2021-07-27|website=ec.europa.eu}}</ref> This implies that this species cannot be imported, bred, transported, commercialized, or intentionally released into the environment in the whole of the European Union.<ref>{{Cite web|title=REGULATION (EU) No 1143/2014 of the European parliament and of the council of 22 October 2014 on the prevention and management of the introduction and spread of invasive alien species|url=https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32014R1143&from=EN
Multiple studies have been published to find out how the damage caused by the settlement — and subsequent overpopulation — of invasive signal crayfish in Europe can be mitigated, including studies regarding effective upstream barriers against signal crayfish that don’t negatively impact the migration of fish,<ref>{{Cite journal |
==References==
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