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Signal crayfish

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Pacifastacus leniusculus
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Class: Malacostraca
Order: Decapoda
Suborder: Pleocyemata
Family: Astacidae
Genus: Pacifastacus
Species:
P. leniusculus
Binomial name
Pacifastacus leniusculus
(Dana, 1852)[2]

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

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A white oval patch at the joint of the fingers of the claw distinguishes this species.

Members of this species are typically 6–9 cm (2.4–3.5 in) long, although sizes up to 16–20 cm (6.3–7.9 in) are possible.[3] A distinctive white to pale blue-green patch is present near the claw hinge,[4] reminiscent of the white flags that signalmen used for directing trains—hence the species' common name.

The 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 eggs. These are then carried under the female's tail until they are ready to hatch in the following spring.[3] Upon hatching, the juveniles undergo three stages of development, passing through (two moults), before they are able to leave their mother. Sexual maturity is reached after two to three years, and the lifespan can extend up to 20 years.[3]

The signal crayfish is an omnivore, with a diet primarily consisting of detritus.[5] Adults can adapt to a broad range of salinity,[6][7]: 71  substrate types and the presence of aquatic vegetation.[6]

Native range

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The signal crayfish is endemic to North America west of the Rocky Mountains, including the Canadian province of British Columbia, and the U.S. states of Washington, Oregon, and Idaho.[8] It was introduced to California in 1912 into the San Lorenzo River watershed and from there rapidly spread throughout the state.[9] 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.[10] Within North America, it has also been introduced to Nevada, and the populations in Utah may be the result of introductions.[8] 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.[1]

Introduction into Europe

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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.[3] At the time, the signal crayfish was not recognized as a carrier of the crayfish plague.[3] 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.[11] 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.[3][12] It was first introduced to Great Britain in 1976,[13][14] 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,[11] 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.[15]

In Europe, the signal crayfish has been included in the list of Invasive Alien Species of Union concern (the Union list) since 2016.[16] This implies that this species cannot be imported, bred, transported, commercialized, or intentionally released into the environment in the whole of the European Union.[17] The signal crayfish is often considered a nuisance species amongst anglers in Europe.[18]

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,[19][20] 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 biocides) and suppression (by means of extensive trapping, electrocution of waterways, and introduction of predatory fish), with eradication being most successful.[20]

References

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  1. ^ a b G. A. Schuster; C. A. Taylor; J. Cordeiro (2010). "Pacifastacus leniusculus". IUCN Red List of Threatened Species. 2010: e.T153648A4526314. doi:10.2305/IUCN.UK.2010-3.RLTS.T153648A4526314.en. Retrieved 7 October 2023.
  2. ^ "Pacifastacus leniusculus (Dana, 1852)". Integrated Taxonomic Information System. Retrieved December 18, 2019.
  3. ^ a b c d e f Stein I. Johnsen & Trond Taugbøl (2010). "NOBANIS – Invasive Alien Species Fact Sheet – Pacifastacus leniusculus" (PDF). Online Database of the European Network on Invasive Alien Species – NOBANIS. Retrieved 10 October 2024.
  4. ^ Mike Averill (1997). "Crayfish in Worcestershire". Worcestershire Record. 1 (2): 4.
  5. ^ Carin A. Bondar; K. Bottriell; K. Zeron; John S. Richardson (2005). "Does trophic position of the omnivorous signal crayfish (Pacifastacus leniusculus) in a stream food web vary with life history stage or density?". Canadian Journal of Fisheries and Aquatic Sciences. 62 (11): 2632–2639. doi:10.1139/F05-167.
  6. ^ a b "Pacifastacus leniusculus". Nemesis. Smithsonian Environmental Research Center. Retrieved 10 October 2024.
  7. ^ Kibenge, Frederick S. B.; Strange, Richard J. (2021-01-01). "Chapter 1 - Introduction to the anatomy and physiology of the major aquatic animal species in aquaculture". In Kibenge, Frederick S. B.; Baldisserotto, Bernardo; Chong, Roger Sie-Maen (eds.). Aquaculture Pharmacology. Academic Press. pp. 1–111. doi:10.1016/B978-0-12-821339-1.00001-5. ISBN 978-0-12-821339-1.
  8. ^ a b James W. Fetzner Jr. (January 14, 2008). "Pacifastacus (Pacifastacus) leniusculus leniusculus (Dana, 1852). Signal crayfish". Crayfish Taxon Browser. Carnegie Museum of Natural History. Retrieved August 8, 2010.
  9. ^ Joe Eaton (May 17, 2005). "Fighting the Bay Area Invasion of Signal Crayfish". Berkeley Daily Planet. Retrieved December 18, 2019.
  10. ^ "PG&E Joins Forces to Save the Endangered Shasta Crayfish". PG&E. Archived from the original on October 19, 2011. Retrieved September 4, 2011.
  11. ^ a b Richard Chadd; Brian Eversham (2010). "Other invertebrates". In Norman Maclean (ed.). Silent Summer: The State of Wildlife in Britain and Ireland. Cambridge University Press. pp. 556–575. ISBN 9781139788694.
  12. ^ Silva, S.; Outón, P.; Nachón, D. J.; Gómez-Sande, P.; Sánchez-Hernández, J.; Vieira-Lanero, R.; Cobo, F. (2017). "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". Nova Acta Científica Compostelana (Bioloxía). 24: 63–68. ISSN 2340-0021.
  13. ^ "Crayfish 'trapping' fails to control invasive species". 13 October 2020.
  14. ^ "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 of Applied Ecology. 12 October 2020. doi:10.1111/1365-2664.13758. S2CID 225116874.
  15. ^ "Signal Crayfish (Pacifastacus leniusculus) Ecological Risk Screening Summary" (PDF). U.S. Fish and Wildlife Service. February 2011.
  16. ^ "List of Invasive Alien Species of Union concern - Environment - European Commission". ec.europa.eu. Retrieved 2021-07-27.
  17. ^ "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".
  18. ^ "Avoiding Crayfish Carp Fishing - Beat the Crayfish!". Carp Squad. 2020-12-14. Retrieved 2022-01-31.
  19. ^ Frings, Roy M.; Vaeßen, Susanne C. K.; Groß, Harald; Roger, Sebastian; Schüttrumpf, Holger; Hollert, Henner (2013-03-01). "A fish-passable barrier to stop the invasion of non-indigenous crayfish". Biological Conservation. 159: 521–529. doi:10.1016/j.biocon.2012.12.014. ISSN 0006-3207.
  20. ^ a b Raphael, Krieg; Alex, King; Armin, Zenker (2020). "Measures to Control Invasive Crayfish Species in Switzerland: A Success Story?". Frontiers in Environmental Science. 8. doi:10.3389/fenvs.2020.609129. ISSN 2296-665X.
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