View source for Signal crayfish

{{Short description|Species of crustacean}}
{{Speciesbox
|name = ''Pacifastacus leniusculus''
|image = Signal crayfish female Pacifastacus leniusculus.JPG
|status = LC
|status_system = IUCN3.1
|status_ref = <ref name=IUCN/>
|genus = Pacifastacus
|species = leniusculus
|authority = ([[James Dwight Dana|Dana]], 1852)<ref>{{ITIS|taxon=''Pacifastacus leniusculus'' (Dana, 1852) |id=97326|access-date=December 18, 2019}}</ref>
}}

The '''signal crayfish''' ('''''Pacifastacus leniusculus''''') is a species of [[crayfish]] indigenous to [[North America]]. Introduced to Europe in the 1960s to supplement the North European ''[[Astacus astacus]]'' fisheries, which were being damaged by [[crayfish plague]], it was subsequently discovered that the signal was itself a carrier of that disease. Consequently, the signal crayfish is now considered an [[invasive species]] across Europe, Japan, and California, having displaced the native species in these regions.

==Description and ecology==
[[File:Kräftklo-1.jpg|thumb|left|A white oval patch at the joint of the fingers of the claw distinguishes this species.]]
Members of this species are typically {{convert|6|-|9|cm|abbr=on}} long, although sizes up to {{convert|16|-|20|cm|sigfig=1|abbr=on}} are possible.<ref name="Nobanis"/> A distinctive white to pale blue-green patch is present near the claw hinge,<ref>{{cite journal|url=http://www.wbrc.org.uk/WorcRecd/Vol1Iss2/crayFish.htm|title=Crayfish in Worcestershire|journal=Worcestershire Record|volume=1|issue=2|year=1997|page=4|author=Mike Averill}}</ref> reminiscent of the white flags that signalmen used for directing trains&mdash;hence the species' common name.

The [[Biological life cycle|lifecycle]] of the signal crayfish is typical for the family [[Astacidae]]. The mating season occurs in the autumn, during which time the female produces around 200 to 400 [[egg (biology)|eggs]]. These are then carried under the female's tail until they are ready to hatch in the following spring.<ref name="Nobanis"/> Upon hatching, the [[juvenile (organism)|juveniles]] undergo three stages of development, passing through (two [[ecdysis|moults]]), before they are able to leave their mother. [[Sexual maturity]] is reached after two to three years, and the [[longevity|lifespan]] can extend up to 20 years.<ref name="Nobanis"/>

The signal crayfish is an [[omnivore]], with a diet primarily consisting of [[detritus]].<ref>{{cite journal |author=Carin A. Bondar|author2=K. Bottriell|author3=K. Zeron|author4=John S. Richardson|year=2005|title=Does trophic position of the omnivorous signal crayfish (''Pacifastacus leniusculus'') in a stream food web vary with life history stage or density? |journal=[[Canadian Journal of Fisheries and Aquatic Sciences]]|volume=62|issue=11|pages=2632–2639|doi=10.1139/F05-167|bibcode=2005CJFAS..62.2632B }}</ref>  Adults can adapt to a [[euryhaline|broad range of salinity]],<ref name=nemesisserc>{{cite web|url=https://invasions.si.edu/nemesis/species_summary/97326|title=''Pacifastacus leniusculus''|website=Nemesis|publisher=Smithsonian Environmental Research Center|access-date=10 October 2024}}</ref><ref>{{cite book|last1=Kibenge |first1=Frederick S. B.|chapter=Chapter 1 - Introduction to the anatomy and physiology of the major aquatic animal species in aquaculture |date=2021-01-01 |doi=10.1016/B978-0-12-821339-1.00001-5|title=Aquaculture Pharmacology |pages=1–111 |editor-last=Kibenge |editor-first=Frederick S. B. |publisher=Academic Press |language=en |isbn=978-0-12-821339-1|last2=Strange |first2=Richard J. |editor2-last=Baldisserotto |editor2-first=Bernardo |editor3-last=Chong |editor3-first=Roger Sie-Maen}}</ref>{{rp|71}} substrate types and the presence of aquatic vegetation.<ref name=nemesisserc/>

==Native range==
The signal crayfish is endemic 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 iucn|author1=G. A. Schuster|author2=C. A. Taylor|author3=J. Cordeiro|title=''Pacifastacus leniusculus''|page=e.T153648A4526314|year=2010|doi=10.2305/IUCN.UK.2010-3.RLTS.T153648A4526314.en|access-date=7 October 2023}}</ref>

==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 mold]] ''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=Stein I. Johnsen|author2=Trond Taugbøl|name-list-style=amp|year=2010|title=NOBANIS – Invasive Alien Species Fact Sheet – ''Pacifastacus leniusculus''|publisher=Online Database of the European Network on Invasive Alien Species – NOBANIS|url=https://www.nobanis.org/globalassets/speciesinfo/p/pacifastacus-leniusculus/pacifastacus_leniusculus1.pdf|access-date=10 October 2024}}</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 | title=A novel 'triple drawdown' method highlights deficiencies in invasive alien crayfish survey and control techniques Daniel D. A. Chadwick Eleri G. Pritchard Paul Bradley Carl D. Sayer Michael A. Chadwick Lawrence J. B. Eagle Jan C. Axmacher |journal=Journal of Applied Ecology | date=12 October 2020 | doi=10.1111/1365-2664.13758 | s2cid=225116874 | doi-access=free }}</ref> and is now widespread across the British mainland as far north as the [[Moray Firth]]. It has also been observed on the [[Isle of Man]], but not in [[Ireland]],<ref name="Summer"/> the last European country to have no alien crayfish.

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 has been included in the list of Invasive Alien Species of Union concern (the Union list) since 2016.<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}}</ref> The signal crayfish is often considered a nuisance species amongst anglers in Europe.<ref>{{Cite web|date=2020-12-14|title=Avoiding Crayfish Carp Fishing - Beat the Crayfish!|url=https://carpsquad.com/avoiding-crayfish-carp-fishing/|access-date=2022-01-31|website=Carp Squad|language=en-US}}</ref>

Multiple studies have been published to identify effective mitigation strategies for the detrimental impact of the settlement — and subsequent overpopulation — of invasive signal crayfish in Europe. This includes studies regarding effective upstream barriers against signal crayfish that do not adversely affect fish migration,<ref>{{Cite journal |last1=Frings |first1=Roy M. |last2=Vaeßen |first2=Susanne C. K. |last3=Groß |first3=Harald |last4=Roger |first4=Sebastian |last5=Schüttrumpf |first5=Holger |last6=Hollert |first6=Henner |date=2013-03-01 |title=A fish-passable barrier to stop the invasion of non-indigenous crayfish |url=https://www.sciencedirect.com/science/article/pii/S0006320712005125 |journal=Biological Conservation |language=en |volume=159 |pages=521–529 |doi=10.1016/j.biocon.2012.12.014 |bibcode=2013BCons.159..521F |issn=0006-3207|url-access=subscription }}</ref><ref name=":0" /> as well as other, aggressive but more efficient approaches which may cause further harm to existing ecosystems, such as eradication (by means of drainage or destruction of waterways, and [[biocide]]s) and suppression (by means of extensive trapping, electrocution of waterways, and introduction of predatory fish), with eradication being most successful.<ref name=":0">{{Cite journal |last1=Raphael |first1=Krieg |last2=Alex |first2=King |last3=Armin |first3=Zenker |date=2020 |title=Measures to Control Invasive Crayfish Species in Switzerland: A Success Story? |journal=Frontiers in Environmental Science |volume=8 |language=English |doi=10.3389/fenvs.2020.609129 |issn=2296-665X|doi-access=free |bibcode=2020FrEnS...809129K }}</ref>

==References==
{{Reflist}}

==External links==
{{Portal|Crustaceans}}
{{Commons category|Pacifastacus leniusculus|''Pacifastacus leniusculus''}}
*{{cite web |url=http://www.vega.org.uk/video/programme/58 |title=Invasion of the Plague Carriers |format=[[RealVideo]] |publisher=The Vega Science Trust |year=2002}}
*{{cite news |url=http://news.bbc.co.uk/2/hi/uk_news/scotland/south_of_scotland/7564004.stm |title='Kill crayfish on sight' appeal |publisher=[[BBC News]] |date =August 15, 2008}}
*{{cite web |url=http://www.crayfish.org.uk/ |title=UK Crayfish Website |publisher=Buglife – The Invertebrate Conservation Trust}}

{{Edible crustaceans}}
{{Taxonbar|from=Q693000}}
{{Authority control}}

[[Category:Astacidae]]
[[Category:Fauna of the Western United States]]
[[Category:Freshwater crustaceans of North America]]
[[Category:Edible crustaceans]]
[[Category:Crustaceans described in 1852]]
[[Category:Taxa named by James Dwight Dana]]