The Signal Crayfish is an aggressive species indigenous to the northwest USA, but which has been introduced into much of Europe and parts of Asia to the detriment of extensive aquatic ecosystems in those regimes.
P. leniusculus has a native range from British Columbia to central California and eastward to the Rocky Mountains. The introduced range includes Britain, much of western Europe including Sweden, most of eastern Europe, part of western Russia and some of the Japanese islands. The introduction of Signal Crayfish to these vast areas was motivated by commercial interests in creating a robust industry for harvesting this species; however, the outcome has produced an ecological nightmare by driving extinct a number of native crayfishes and producing ecological imbalance from this voracious competitor.
Length of males measures to 16 cm from end of telson to rostrum tip, with females about three quarters of this size. Body mass varies between 55 and 115 grams. Exterior color varies between brownish blue, reddish brown, and less commonly a plain brown. There are smooth rostrum flanks; the acumen is very quite sharply pointed and manifests significant shoulders. A median carina runs entire length. Claws are massive and smooth, the underside being red; with a lone inner tubercle (relative to the fixed finger).A distinctive white patch decorates the top of the join of fixed and movable fingers.
HABITAT AND ECOLOGY
P. leniusculus exploits a gamut of habitats including streams, major rivers and sub-alpine lakes; (Lewis) it is able to adapt to warmer waters, pH above six and even slightly saline water bodies. This aggressive species can colonize streams at the rate of one kilometer per annum. (Stanton) Burrows can occur at very high organism densities, up to 14 per square meter; moreover, this dense clustering of burrows can compromise streambank integrity, in some cases causing severe bank collapse and subsequent erosion. This phenomenon has been particularly observed in Europe, where there are differing bank forms sometimes lacking in the natural burrow crevices of the species native range; therefore, in Europe, much more extensive burrowing has been noted compared to use of streambed armor in the Western USA. (Sibley) Colonization of new area is facilitated by P. leniusculus' ability to creep overland and around terrestrial barriers.
Although polytrophic in diet, faunal intake is preferred by this crayfish, which has caused major attrition to certain macro-invertebrates, benthic fish and aquatic vegetation. (Nyström) For example, P.leniusculus has been shown to decimate Atlantic salmon populations.. Pacifastacus nigrescens, endemic to the western USA, went extinct partially due to interspecific competition with the Signal Crayfish, which humans introduced into its range. Signal Crayfish has caused a contraction in the range of the western USA narrowly endemic P. fortis. (Taylor).
There is no concern regarding the viability of this species; rather, there are significant issues regarding Signal Crayfish as an invasive species, threatening the existence of numerous other taxa. Introduced into Japan as early as 1926, this crayfish has been cultivated in Asia and Europe for its substantial catches, exceeding 400 tons per year in Europe. There are literally no management techniques known for the successful management of P. leniusculus. Trapping is size selective, with the result that smaller individuals elude Preventing the further introduction of Signal Crayfish into new bodies of water is the most important single element of future decision-making regarding this species. Public awareness of the ecological risks this species pose and identifying new populations are key components to arrest the spread of this species. Current research is examining the use of pheromones to attract male P. leniusculus into traps. Tough legislation has been invoked to P. leniusculus in Britain, which labels it a pest and bans the keeping of it in Scotland, Wales and much of England. Nevertheless, P. leniusculus colonizes new waters and threatens the extinction of the indigenous UK crayfish population (Hiley).
- C.Michael Hogan. 2008. Signal Crayfish, Pacifastacus leniusculus. GlobalTwitcher. ed. N.Stromberg
- S.D.Lewis (2002) Pacifastacus, in Holdich, D. M. (Ed.), Biology of freshwater crayfish. Blackwell Science, Oxford: 511-540
- J.A. Stanton (2004) Burrowing behaviour and movements of the signal crayfish. PhD. thesis, University of Leicester, UK. 169 p
- P. Sibley (2000) Signal crayfish management in the River Wreake catchment, in D.Rogers & J.Brickland (eds), Crayfish Conference Leeds. Environment Agency, Leeds: 95-108.
- P.Nystrom (1999). Ecological impact of introduced and native crayfish on freshwater communities: European perspectives. In Gherardi, F. and Holdich, D.M. (eds.) Crustacean Issues 11: Crayfish in Europe as Alien Species (How to make the best of a bad situation?) A.A. Balkema, Rotterdam, Netherlands: 63-85
- C.A.Taylor (2002) Taxonomy and conservation of native crayfish stocks, in D.M. Holdich (ed.), Biology of freshwater crayfish. Blackwell Science, Oxford: 236-257
- P.D. Hiley (2003) The slow quiet invasion of signal crayfish (Pacifastacus leniusculus) in England: prospects for the white-clawed crayfish (Austropotamobius pallipes), in D.M. Holdich & P.J. Sibley (eds), Management & Conservation of Crayfish. Proceedings of conference in Nottingham on 7 November, 2002. Environment Agency, Bristol: 127-138
Pacifastacus leniculus has been introduced into many countries throughout Europe, as well as to California, Nevada and Utah in the USA. This species was introduced during the 1970s and 1980s, is widely cultivated and is established in the wild, from where it is harvested (Harlio?lu and Holdich 2001).
Regularity: Regularly occurring
Type of Residency: Year-round
Regularity: Regularly occurring
Type of Residency: Year-round
Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) Ranges from British Columbia to California; introduced into Europe and Japan (Hobbs, 1989). Pacifastacus leniculus has been introduced into many countries throughout Europe and California, Nevada and Utah in the USA. This species was introduced during the 1970s and 1980s, is widely cultivated and is established in the wild, from where it is harvested (Harlioglu and Holdich, 2001). Pacifastacus leniusculus leniusculus is distributed throughout British Columbia, California, Idaho, Oregon, and Washington. Pacifastacus leniusculus klamathensis is distributed throughout British Columbia in Canada, Idaho and south to central California in the USA. Pacifastacus leniusculus trowbridgii is distributed throughout British Columbia in Canada and California, Idaho, Oregon and Washington in the USA, and has been introduced into California and Nevada in the USA, and also introduced into Japan.
Habitat and Ecology
Tolerance experiments indicated that O+ juveniles and adults are well adapted for surviving salinities of at least 21 in the long term and of being transferred directly back into freshwater. However, their ability to colonize the estuarine environment may be restricted to areas of low salinity (i.e. 7) due to the adverse effects of seawater on egg development and hatching (Holdich et al. 1997).
Comments: Generally prefers cool water with current over rocky bottom; does not burrow; is highly adaptable and can be found in a wide variety of habitats including coastal and mountain streams and lakes, reservoirs, and the saline waters in river deltas (Hogger, 1988).
Non-Migrant: No. All populations of this species make significant seasonal migrations.
Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).
Locally Migrant: No. No populations of this species make annual migrations of over 200 km.
Number of Occurrences
Note: For many non-migratory species, occurrences are roughly equivalent to populations.
Estimated Number of Occurrences: > 300
Comments: Extremely common species. Harvested population in Lake Billy Chinook, Oregon, found to have mean density of 0.24 to 1.13 per square meter with total abundance 36 million (+- 8 million) individuals (Lewis and Horton, 1996). Introductions have been made throughout California, Nevada and Utah, as well as various parts of Europe (Rogers, 2005).
Comments: Extremely common species. Harvested population in Lake Billy Chinook, Oregon, found to have mean density of 0.24 to 1.13 per square meter with total abundance 36 million (+- 8 million) individuals (Lewis and Horton, 1996). There is no population information for Pacifastacus leniusculus, however the signal crayfish is an important invasive species which has a wide distribution and is likely to exceed 1 million mature individuals in the wild.
Life History and Behavior
Lewis and Horton (1996) found for populations in Oregon that hatching began during the second week in April and eight age classes identified.
Molecular Biology and Genetics
Barcode data: Pacifastacus leniusculus
There is 1 barcode sequence available from BOLD and GenBank. Below is the sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species. See the BOLD taxonomy browser for more complete information about this specimen. Other sequences that do not yet meet barcode criteria may also be available.
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Download FASTA File
Statistics of barcoding coverage: Pacifastacus leniusculus
Public Records: 1
Specimens with Barcodes: 1
Species With Barcodes: 1
IUCN Red List Assessment
Red List Category
Red List Criteria
National NatureServe Conservation Status
Rounded National Status Rank: N5 - Secure
Rounded National Status Rank: N5 - Secure
NatureServe Conservation Status
Rounded Global Status Rank: G5 - Secure
Reasons: This is an invasive, r-selected and widespread species which is able to out-compete native species often growing to a larger size. This species is also resistant to the crayfish plague but is a carrier the disease and is able to thrive in a wide reange of habitats. It has been introduced into Europe and outside of its native range in the USA. No conservation measures are required.
Degree of Threat: Low
Comments: There are no known threats.
Pacifastacus leniusculus klamathensis: NatureServe G5T5, AFS Currently Stable (Taylor et al. 2007).
Pacifastacus leniusculus leniusculus: NatureServe G5T5, AFS Currently Stable (Taylor et al. 2007).
Pacifastacus leniusculus trowbridgii: NatureServe G5T5, AFS Currently Stable (Taylor et al. 2007).
Relevance to Humans and Ecosystems
Comments: Species harvested in some states (Lewis and Horton, 1996).
The signal crayfish, Pacifastacus leniusculus, is a North American species of crayfish. It was introduced to Europe in the 1960s to supplement the Scandinavian 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 and Japan, ousting native species there.
Description and ecology
Members of this species are typically 6–9 centimetres (2.4–3.5 in) long, although sizes up to 16–18 cm (6.3–7.1 in) are possible. They are bluish-brown to reddish-brown in colour with robust, large, smooth claws. They have a white to pale blue-green patch near the claw hinge, like the white flags that signalmen used for directing trains—hence the name.
The life cycle of the signal crayfish is typical for the family Astacidae. Around 200–400 eggs are laid after mating in the autumn, and are carried under the female's tail until they are ready to hatch the following spring. The eggs hatch into juveniles, which pass through three moults before leaving their mother. Sexual maturity is reached after two to three years, and the life span can be up to 20 years.
The signal crayfish is native 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. It was introduced to California in 1912 into the San Lorenzo River watershed and from there rapidly spread throughout the state. The only native crayfish remaining in California is the Shasta crayfish (Pacifastacus fortis), where efforts are being made to create a barrier to Signal crayfish invasion. Within North America, it has also been introduced to Nevada, and the populations in Utah may be the results of introductions. It is listed as a species of Least Concern on the IUCN Red List.
Introduction into Europe
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. It was not realised at the time that the signal crayfish was a carrier of the crayfish plague. 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.
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. It was first introduced to Great Britain in 1976, 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.
- "Pacifastacus leniusculus (Dana, 1852)". Integrated Taxonomic Information System. Retrieved August 28, 2010.
- Trond Taugbøl & Stein I. Johnsen (2006). "Invasive Alien Species Fact Sheet – Pacifastacus leniusculus" (PDF). Online Database of the North European and Baltic Network on Invasive Alien Species. NOBANIS – European Network on Invasive Species. Retrieved August 28, 2010.
- Mike Averill (1997). "Crayfish in Worcestershire". Worcestershire Record 2: 4.
- 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?" (PDF). Canadian Journal of Fisheries and Aquatic Sciences 62: 2632–2639. doi:10.1139/F05-167.
- 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.
- Joe Eaton (2005-05-17). "Fighting the Bay Area Invasion of Signal Crayfish". Berkeley Daily Planet. Retrieved 2011-09-04.
- "PG&E Joins Forces to Save the Endangered Shasta Crayfish". PG&E. Retrieved 2011-09-04.
- G. A. Schuster, C. A. Taylor & J. Cordeiro (2010). "Pacifastacus leniusculus". IUCN Red List of Threatened Species. Version 3.1. International Union for Conservation of Nature. Retrieved October 6, 2010.
- Richard Chadd & Brian Eversham (2010). "Other invertebrates". In Norman Maclean. Silent Summer: The State of Wildlife in Britain and Ireland. Cambridge University Press. pp. 556–575.
Names and Taxonomy
Comments: Economically referenced as the "noble crayfish", without strict adherence to the several subspecies.