Invasion History

First Non-native North American Tidal Record: 1959
First Non-native West Coast Tidal Record: 1959
First Non-native East/Gulf Coast Tidal Record:

General Invasion History:

Pacifastacus leniusculus is native to northwestern North America from Oregon to British Columbia. The southern boundary of the native range is unclear. Museum specimens from the Klamath and Eel River drainages in Northern California are undated (Taylor et al. 1996; U.S. Museum of Natural History 2007). The Signal Crayfish was introduced to various watersheds in California, including the San Francisco Bay watershed and delta (Cohen and Carlton 1995).

North American Invasion History:

Invasion History on the West Coast:

Pacifastacus leniusculus was introduced to various California watersheds, possibly as early as 1898, in San Francisco. An official transplant was made in 1912 to hatcheries in Santa Cruz County, and in later years, they were introduced to the Sacramento-San Joaquin watershed. They were present in the Delta by 1959, and are now abundant (Riegel 1959). Other California locations include the Monterey Bay watershed, and upper reaches of the Sacramento watershed in the Sierras (USGS Nonindigenous Aquatic Species Program 2010). Two records near the coast were from the Carmel River and the Little Sur Rivers, south of Monterey Bay, two and one miles from the ocean, respectively (Riegel 1959).

In 2002, one specimen was caught in the Buskin River on Kodiak Island, Alaska (USGS Nonindigenous Aquatic Species Program 2011). This could have been a bait release.

Invasion History Elsewhere in the World:

In the 1860s, the fungus Aphanomyces astaci (Crayfish Plague) spread throughout Europe, killing the native crayfish (Astacus astacus) and other species. This disease was probably brought from North America with crayfish sold as food. Disease-resistant North American crayfish were stocked in many locations. Pacifastacus leniusculus was introduced to Sweden in 1959, and were widely transplanted into northern European freshwaters and are now present from Spain to Finland, with isolated populations in Greece (Holdich et al. 2009). It occurs in the Gulf of Bothnia, Baltic Sea (Olenin and Leppakoski 2000), but the extent to which it inhabits and disperses through estuarine waters is unclear (Holdich et al. 1997). Pacifiastcus leniusculus is established in the upper Danube drainage near Koszeg, Hungary (Puky et al. 2005). It also occurs in the Czech Republic and Austria, but has not been reported from the lower Danube or elsewhere in the Black Sea watershed.

Pacifastacus leniusculus stock from the Columbia River was introduced to Hokkaido and Honshu, Japan, between 1926 and 1930, and it is now widespread, especially in Hokkaido (Uso et al. 2007).


Male crayfish of the genus Pacifastacus (Signal Crayfish) lack hooks on the ischia (3rd segment) of the walking legs, while females lack the annulus ventralis (seminal receptacle), which in cambarid crayfish, is located between the 4th and 5th pairs of walking legs (Hobbs 1991). The margin of the rostrum in P. leniusculus is smooth. The Signal Crayfish matures at 60 mm and occasionally reaches 160 mm. The overall color of the animal is dark brown, but a turquoise and white patch at the base of the claw is distinctive (Riegel 1959; Taugbøl and Johnsen 2006).


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Arthropoda
Subphylum:   Crustacea
Class:   Malacostraca
Subclass:   Eumalacostraca
Superorder:   Eucarida
Order:   Decapoda
Suborder:   Pleocyemata
Infraorder:   Stenopodidea
Superfamily:   Astacoidea
Family:   Astacidae
Genus:   Pacifastacus
Species:   leniusculus


Astacus leniusculus (Dana, 1852)
Potamobius leniusculus (Ortmann, 1902)

Potentially Misidentified Species

Orconectes virilis
Virile Crayfish, Midwest native, introduced to East Coast, West Coast, and Europe

Pacifastacus klamathensis
Klamath Crayfish, native to Klamath and Eel basins, northern California and Oregon

Pacifiastacus fortis
Shasta Crayfish, California native, upper Sacramento basin



Life History- Freshwater crayfish mate by internal fertilization, with the male attaching spermatophores to the space between the 4th and 5th walking legs. The female curls her abdomen far forward, to create a chamber in which the eggs are driven by the pleopods. The mass of eggs becomes attached under the tail. Larval development takes place inside the egg and the young hatch as miniature adults (Barnes 1983).

Ecology- Pacifastacus leniusculus inhabits streams, ponds and lakes in a variety of habitats, including rocky, muddy, and vegetated areas (Taugbøl and Johnsen 2006). If soft sediment is present, it digs burrows. It is tolerant of salinities up to 28 PSU, but females with eggs have not been seen at salinities above 7 PSU (Holdich et al. 1997).


aquatic plants, freshwater invertebrates, carrion


fishes, turtles, snakes, raccoons, otters, birds


Other crayfish species

Trophic Status:




General HabitatFresh (nontidal) MarshNone
General HabitatGrass BedNone
General HabitatCoarse Woody DebrisNone
General HabitatSwampNone
General HabitatNontidal FreshwaterNone
General HabitatTidal Fresh MarshNone
General HabitatRockyNone
Salinity RangeLimnetic0-0.5 PSU
Salinity RangeOligohaline0.5-5 PSU
Salinity RangeMesohaline5-18 PSU
Salinity RangePolyhaline18-30 PSU
Tidal RangeSubtidalNone
Vertical HabitatEpibenthicNone

Tolerances and Life History Parameters

Minimum Temperature (ºC)7.5Westhoff and Rosenberger 2016
Maximum Temperature (ºC)32C. DALE BECKER, ROBERT G. GENOWAY, and J. A. MERRILL 1975, Resistance of a Northwestern Crayfish, Pacifastacus leniusculus (Dana), to Elevated Temperatures. Transactions of the American Fisheries Society 1975;104:374–387
Minimum Salinity (‰)0This a freshwater species.
Maximum Salinity (‰)28~60% survival over 9 weeks (Holdich et al. 1997)
Maximum Reproductive Salinity7Maximum salinity in which eggs on berried females hatched (Holdich et al. 1997)
Maximum Length (mm)160ISSG Global Invasive Species database 2011
Broad Temperature RangeNoneCold temperate-Warm temperate
Broad Salinity RangeNoneNontidal Limnetic-Polyhaline

General Impacts

Pacifastacus leniusculus (Signal Crayfish) has had a significant positive economic impact as a fisheries species, but it has had negative impacts as a competitor with native species in California, Europe and Japan. In Europe, it is also a vector for the spread of the crayfish plague (Cohen and Carlton 1995; Usio et al. 2007; Holdich et al. 2009). In Sweden, the estimated cost of impacts from the Signal Crayfish and the crayfish plague was estimated at about 53-88 million US dollars (Gren et al. 2009).

Economic Impacts

Fisheries- Pacifastacus leniusculus is the major crayfish species caught in the San Francisco Bay Delta, supporting a fishery of 250 tons annually (Cohen and Carlton 1995). Pacifastacus leniusculus supports substantial fisheries in Sweden and other northern European countries (Taugbøl and Johnsen 2006).

Ecological Impacts

Competition- In the San Francisco Bay watershed, Pacifastacus leniusculus may have contributed to the extinction of a native crayfish (P. nigrescens, Sooty Crayfish), and is considered to be a competitor threatening the native crayfish P. fortis (Shasta Crayfish) (Cohen and Carlton 1995). Pacifastacus leniusculus displaced the native crayfishes (Astacus astacus, Austropotamobius pallipes) in Europe (Lowery and Holdich 1999; Holdich et al. 2010). In Japan, it is reported to compete and prey on the country's only native crayfish (Cambaroides japonicus) (Usio et al. 2007).

Disease Vector- Pacifastacus leniusculus is a major vector for the spread of the 'Crayfish Plague' fungus, Aphanomyces astaci, which has greatly reduced the abundance and range of native crayfishes in Europe (Lowery and Holdich 1989; Holdich et al. 2009).

Habitat Change- Burrowing by P. leniusculus has been reported to cause erosion at the rate of 1 m per year on the River Lark, England (Stancliffe-Vaughan, 2009, cited by Holdich et al. 2009).

Regional Impacts

P090San Francisco BayEconomic ImpactFisheries
Pacifastacus leniusculus is the major crayfish species caught in the San Francisco Bay Delta, supporting a fishery of 250 tons annually (Cohen and Carlton 1995).
P090San Francisco BayEcological ImpactCompetition
Pacifastacus leniusculus may have contributed to the extinction of a native crayfish (P. nigrescens, Sooty Crayfish), and is considered to be a competitor threatening another native crayfish, P. fortis (Shasta Crayfish) (Cohen and Carlton 1995).
B-XIIINoneEconomic ImpactFisheries
Pacifastacus leniusculus supports substantial fisheries in Sweden and other northern European countries. However, the native A. astacus is still preferred by many customers and sells for a higher price in Sweden and Finland (Holdich et al. 2009). Gren et al. (2009) estimated the loses for fisheries in Sweden due to the crayfish plague (Aphanomyces astaci) and the displacement of native crayfish by P. leniusculus at 365 to 598 million Swedish kroner (53-88 million US dollars).
B-XIIINoneEcological ImpactCompetition
Pacifastacus leniusculus has displaced the native Noble Crayfish (Astacus astacus) in Sweden and Finland (Holdich et al. 2009).
B-XIIINoneEcological ImpactParasite/Predator Vector
Disease Vector- Pacifastacus leniusculus is a major vector for the spread of the 'Crayfish Plague' fungus, Aphanomyces astaci, which has greatly reduced the abundance and range of native crayfish in Europe (Lowery and Holdich 1989).

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
P293 _CDA_P293 (Strait of Georgia) 0 Native Estab
P120 Eel River 1959 Def Estab
P140 Klamath River 0 Def Estab
P150 Rogue River 0 Native Estab
P260 Columbia River 0 Native Estab
P090 San Francisco Bay 1959 Def Estab
P290 Puget Sound 0 Native Estab
P280 Grays Harbor 0 Native Estab
P220 Siletz Bay 0 Native Estab
B-XIII None 1959 Def Estab
P093 _CDA_P093 (San Pablo Bay) 1959 Def Estab
P076 _CDA_P076 (Carmel) 1959 Def Estab
P073 _CDA_P073 (Central Coastal) 1959 Def Estab
B-VIII None 2016 Def Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude


Associated Press (12/2021) Lummi Nation declares disaster after invasive crab arrives, Seattle Times <missing volume>: <missing location>

Barnes, Robert D. (1983) Invertebrate Zoology, Saunders, Philadelphia. Pp. 883

Capinha, Cesar; Anastacio, Pedro; Tenedorio, Jose Antonio (2012) Predicting the impact of climate change on the invasive decapods of the Iberian inland waters: an assessment of reliability, Biological Invasions 14: 1737-1751

Capinha, Cesar; Larson, Eric R.; Tricarico, Elena; Olden, Julian D.; Gherardi, Francesca (2013) Effects of climate change, invasive species, and disease on the distribution of native European crayfishes, Conservation Biology 27(4): 731-740

Cohen, Andrew N.; Carlton, James T. (1995) Nonindigenous aquatic species in a United States estuary: a case study of the biological invasions of the San Francisco Bay and Delta, U.S. Fish and Wildlife Service and National Sea Grant College Program (Connecticut Sea Grant), Washington DC, Silver Spring MD.. Pp. <missing location>

Eames, I.; Landeryou, M; Greig, A.; Snellings, J. (2008) Continuous flushing of contaminants from ballast water tanks., Marine Pollution Bulletin 56: 250-260

González-Sánchez, K.; Flores-Alvarado, B.; Montiel-Barrantes,P., Gómez-Arce, G.; Alvarado, J. J. (2021) Ascidian diversity of Costa Rica, including new records for the North Pacific, Revista de Biologia Tropical 69(Suppl. 2): S234-S245

Grabowski, Michal; Jazdewski, Kryzystof; Konopacka, Alicia, (2005) Alien Crustacea In Polish waters - Introduction and Decapoda., Oceanological and Hydrobiological Studies 34(2): 43-61

Gren, Ing-Marie; Isacs, Lina; Carlsson, Mattias (2009) Costs of alien invasive species in Sweden, Ambio 38(3): 135-140

Haddaway, Neal R. and 6 authros (2012) Predatory functional response and prey choice identify predation differences between native/invasive and parasitised/unparasitised crayfish, PLOS ONE 7(2): e32229

Hobbs, H. H. III (1991) Ecology and Classifiaction of North American Freshwater Invertebrates, Academic Press, San Diego. Pp. 823-858

Holdich, D. M.; Harlioglu; Firkins, I. (1997) Salinity adaptations of crayfish in British waters with particular reference to Austropotamobius pallipes, Astacus leptodactylus and Pacifastacus leniusculus, Estuarine, Coastal and Shelf Science 44: 147-154

Holdich, D. M.; Reynolds, J. D.; Souty-Grosset, C.; Sibley, P. J. (2009) A review of the ever increasing threat to European crayfish from non-indigenous crayfish species, Knowledge and Management of Aquatic Ecosystems 11: 394-395

Jazdzewski, Krzysztof; Konopacka, Alicja; Grabowski, Michal; (2005) Native and alien malacostracan Crustacea along the Polish Baltic Sea coast In the twentieth century., Oceanological and Hydrobiological Studies 34(Suppl. 1.): 175-193

Laverty, Ciaran; Nentwig, Wolfgang; Dick, Jaimie T.A.; Lucy, Frances E. (2015) Alien aquatics in Europe: assessing the relative environmental and socioeconomic impacts of invasive aquatic macroinvertebrates and other taxa, Management of Biological Invasions 6: In Press

Light, Theo; Grosholtz, Ted; Moyle, Peter (2005) Delta ecological survey (phase1): Nonindigenous aquatic species in the Sacramento-San Joaquin Delta, a literature review, In: None(Eds.) None. , Stockton, CA. Pp. <missing location>

Lodge, David M. and 17 authors (2012) Global introductions of crayfishes: evaluating the impact of species invasions on ecosystem services, Annual Review of Ecology and Systematics 43: 449-472

Lowery, R. S.; Holdich, D. M. (1989) Pacifiastacus lenisculus in North America, with details of the distribution of introduced and native crayfish species in Europe., In: Holdich, D. M., and Lowery, R. S.(Eds.) Freshwater Crayfish: Biology, Management, and Exploitation.. , London. Pp. 283-308

Lucena, Rudá Amorim; Christoffersen, Martin Lindsey (2018) Anoplodactylus (Pycnogonida: Phoxichilidiidae) from Brazil, ew records and two new species, Turkish Journal of Zoology 42: 372-388

Mestre, Alexandre and 16 authors (2014) Invasion biology in non-free-living species: interactions between abiotic (climatic) and biotic (host availability) factors in geographical space in crayfish commensals (Ostracoda, Entocytheridae), Ecology and Evolution 3(16): 5237-5253 5253

2000-2016 Inventory of Baltic Sea alien species.

Orlova, M. I.; Kommendatov, A. Yu. (2013) [The use of laboratory populations of the invasive New Zealand mollusk, Potamopyrgus antipodarum (Gastropoda, Hydrobiidae), for assessment of its euryhalinity and physical modelling of invasion in relation to the salinity gradient], Zoologicheskii Zhurnal 92(7): 759-770

Oscoz, Javier; Tomás, Pedro; Durán, Concha (2009) Review and new records of non-indigenous freshwater invertebrates in the Ebro River basin (Northeast Spain), Aquatic Invasions 5(3): 263-284

Pearl, Christopher A.; Adams, Michael J.; McCreary,Brome (2013) Habitat and co-occurrence of native and invasive crayfish in the Pacific Northwest, USA, Aquatic Invasions 8: in press

Puky, M.; Reynolds, J. D.; Schád, P. (2005) Native and alien decapoda species in Hungary: distribution, status, conservation importance, Bulletin Francais de la Peche et de la Pisciculture 376-377: 553-568

Riegel, J. A. (1959) The systematics and distribution of crayfishes in California, California Fish and Game 45(1): 29-50

Skov, Christian and 5 authors (2011) Non-indigenous signal crayfish Pacifastacus leniusculus are now common in Danish streams: preliminary status for national distribution and protective actions, Biological Invasions 13: 1269-1274

Sytsma, Mark D.; Cordell, Jeffrey R.; Chapman, John W.; Draheim, Robyn, C. (2004) <missing title>, Center for Lakes and Reservoirs, Portland State University, Portland OR. Pp. <missing location>

2006 NOBANIS: Invasive Alien Species Fact Sheet: <i>Pacifastacus leniusculus</i>. Online Database of the North European and Baltic Network on Invasive Alien Species: NOBANIS

Taylor, Christopher A.; Warren, Melvin L.; Fitzpatrick, J. F., Jr., Hobbs, Horton H.., Jezerinac, Raymond F., Pflieger, William L., Robison, Henry W. (1996) Conservation status of crayfishes of the United States and Canada, Fisheries 21(4): 25-37

2002-2021 Invertebrate Zoology Collections Database. <missing description>

Usio, N.; Nakata, Kazuyoshi; Kitano, Satoshi (2007) Distribution and control status of the invasive signal crayfish Pacifastacus leniusculus in Japan, Japanese Journal of Limnology 68: 471-482