The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

Pacifastacus leniusculus
Pacifastacus leniusculus
(Signal Crayfish)
Native Transplant

Copyright Info
Pacifastacus leniusculus (Dana, 1852)

Common name: Signal Crayfish

Taxonomy: available through www.itis.govITIS logo

Identification: The dorsal surface of Signal Crayfish is typically brownish-tan in coloration. Although most individuals of Pacifastacus leniusculus conform to this, coloration may be highly variable based on locality and can range from bright red to blue in some cases (Larson and Olden 2011). A bright red coloration on the underside of claws, and a white or turquoise colored patch present at the base of each claw joint is distinctive to the Signal Crayfish (Riegel 1959; Larson and Olden 2011). Additionally, the surface of the carapace and claws are smooth, lacking the pronounced bumps that are typical of other nonnative crayfish (Orconectes rusticus and O. virilis) introduced to the Pacific Northwest (Larson and Olden 2011). Signal Crayfish can be distinguished from the White Claw Crayfish (Austropotamobius pallipes) in Europe by the absence of spines along the cervical groove (margin between the head and body) (Pöckl et al. 2006).

Pacifastacus leniusculus (Dana, 1852), which is part of the subgenus Pacifastacus, is divided into three subspecies; leniusculus, klamathensis (Stimpson, 1857), and trowbridgii (Stimpson, 1857). Initially described as separate species, the similar, yet highly variable morphology shared by these subspecies has challenged taxonomists for decades (Larson et al. 2012). Miller (1960) was the first to describe these as subspecies of P. leniusculus. Genetic studies have since identified P. l. leniusculus and P. l. trowbridgii as being the most similar of the three subspecies, while P. l. klamathensis is the most distinct (Agerberg and Jansson 1995

Physical features key in differentiating P. l. leniusculus from P. l. trowbridgii include the presence of sharp spines on the post orbital ridge and a relatively narrow carapace. In contrast, P. l. trowbridgii typically have a robust carapace with rounded tubercles on their post orbital ridge. Small tubercles rather than spines are present in P. l. klamathensis’ post orbital ridge, and the white to blue-green pigmentation commonly found on the chelae of the other subspecies is often absent. Additionally, the rostrum of P. l. klamathensis is very wide relative to the length of its acumen (Riegel 1959; Miller 1960; Larson and Williams 2015). Due to the difficulty and complexity of distinguishing these subspecies, Larson et al. (2012) summarized Miller’s (1960) identifying criteria (Larson et al. 2012 - appendix S1). The characteristics summarized by Larson et al. (2012) are illustrated in the table below for comparisons.

Summarized identifying characteristics of Signal Crayfish subspecies (Larson et al. 2012).
  Signal Crayfish
P. l. leniusculus
Columbia River Signal Crayfish
P. l. trowbridgii
Klamath Signal Crayfish
P. l. klamathensis
Claws (chelae) Wide with long finger, short and highly convex palm Wide with intermediate finger appendage, and palm slightly to greatly convex Wide with intermediate finger length and palm slightly to greatly convex
Acumen length Long relative to width at rostral spines Intermediate relative to width at rostral spines Short relative to width at rostral spines
Sides of rostrum Strongly converging Converging to nearly parallel Converging to nearly parallel
Rostrum length Long relative to total carapace length Long relative to total carapace length Short relative to total carapace length
Post orbital spines Long Short or tubercle-like Short or tubercle-like
Areola length Short relative to total length Intermediate relative to total length Intermediate relative to total length
Head (cephalon) length Long Intermediate relative to total length Intermediate relative to total length
Carapace Cylindrical (narrow relative to orbital carapace length) Wide relative to orbital carapace length Wide relative to orbital carapace length


Size: The average Signal Crayfish attains a carapace length (CL) of 50-70 mm (Capurro et al. 2007).

Native Range: Pacifastacus leniusculus is a wide-ranging species native to the Northwestern United States (Larson and Olden 2011). Much of the Signal Crayfish’s presumed native range is found within the Columbia River Basin. From the Columbia River’s lower estuary, the native range spans northwest up the mainstem to tributaries that reach into Washington, Oregon, Idaho, and British Columbia. The native range extends south from the Columbia River along Oregon’s coast where the Klamath River and its drainages form its southern boundary (Miller 1960; Larson et al. 2012).

The subspecies of Signal Crayfish are believed to have once been geographically isolated populations (Hobbs 1988). Mixing due to the prevalence of early introductions, a lack of historical records, and hybridization between subspecies has made describing their native range and taxonomic status problematic (Hobbs 1988; Lowery and Holdich 1988; Larson and Williams 2015). This has led the subspecies of Signal Crayfish to be commonly regarded as a single species (Hobbs 1988). Genetic tests have begun to shed light on this, but the extent of the native distributions of Signal Crayfish subspecies continues to be a contested subject (Larson and Williams 2015).

The subspecies P. l. leniusculus, is believed to be native to the lower Columbia River and its tributaries (including the Willamette River) in western Oregon and Washington state. It is also assumed to be native to the Umpqua River, which is believed to have had a historic drainage connection to the Willamette (Miller 1960; Larson and Williams 2015). Based on Miller’s (1960) accounts, it is probable that Pacifastacus leniusculus trowbridgii is also native to the lower Columbia River basin, and nearby coastal rivers, such as the Umpqua, which were likely once connected via stream capture (Miller 1960; Larson et al. 2012; Larson and Williams 2015). Pacifastacus leniusculus klamathensis is presumed to be native to the Klamath River in Northern California and Southern Oregon, but the extent of its native range beyond this basin is unknown due to decades of introductions that have resulted in the mixing of populations.

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Nonindigenous Occurrences:

Table 1. States with nonindigenous occurrences, the earliest and latest observations in each state, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Pacifastacus leniusculus are found here.

StateFirst ObservedLast ObservedTotal HUCs with observations†HUCs with observations†
AK200220151Kodiak-Afognak Islands
CA1895201913California Region; Central California Coastal; Lake Tahoe; Lower Pit; Lower Sacramento; Monterey Bay; North Fork Feather; Salinas; San Pablo Bay; Tomales-Drake Bays; Truckee; Upper Bear; Upper King
MN202320231Long Prairie
NV196219891Middle Carson

Table last updated 6/18/2024

† Populations may not be currently present.

* HUCs are not listed for states where the observation(s) cannot be approximated to a HUC (e.g. state centroids or Canadian provinces).

Ecology: Pacifastacus leniusculus typically seek shelter in rocky crevices or woody debris within streambeds and littoral zones (Holdich and Lowery 1988). The signal crayfish is considered a non-burrowing crayfish (Shimizu and Goldman 1983), although they are known to construct shallow borrows. Burrowing activity is most common in crayfish smaller than 50 mm and the least common in larger males (Guan 2010). The population density of Signal Crayfish is correlated with refugee availability (Flint 1975), and waterbodies with rocky littoral zones support far greater densities than places with clay banks (Shimizu and Goldman 1983).

The Signal Crayfish occupies a range of habitats throughout its native and non-native distribution (Goldman and Rundquist 1977; Holdich and lowery 1988). Though P. leniusculus prefers low gradient streams typical of agricultural low-lands in western Oregon (Avault 1973), they inhabit both coastal and upland streams, lakes, and rivers (Lowery and Holdich 1988). Signal crayfish can be found in habitats ranging from clear, shallow coastal streams (Lowery and Holdich 1988), to major rivers with high turbidity (Ibbotson and Furse 1995), as well as eutrophic and oligotrophic lakes and reservoirs (Holdich and Lowery 1988). Pacifastacus leniusculus also occupies the saline and often turbid waters of major river deltas (Shimizu and Goldman 1983). Wheatly & McMahon (1983) revealed via a laboratory study that Signal Crayfish can occupy waterways with salinity as high as ~26 ppt (75% seawater), for several days. Additionally, Miller (1965) noted that Signal Crayfish have been observed copulating, molting, and laying eggs in brackish water.

The breeding cycle of the Signal Crayfish follows that of most temperate zone crayfish. Copulation occurs during the autumn months (September or October), and females carry the eggs throughout the winter (Holdich and Lowery 1988). Eggs then typically hatch in March and April as the water warms (Shimizu and Goldman 1983). The young from populations residing in cooler waters may hatch later in the year (June and July), since growth is temperature dependent. Once hatched, P. leniusculus grow rapidly and most individuals mature during their second summer. The time to maturity may also be delayed by cooler water temperatures, such as that of Lake Tahoe. Here, males may mature during their third summer, while females may not mature until fourth (Holdich and Lowery 1988). Abrahamsson and Goldman (1970) estimated that male and female P. leniusculus in the Sacramento River, CA., mature when they reach the size of 29-37 mm CL and 25-35 mm CL, respectively. Crayfish growth is also density dependent, which often results in small, newly established populations of P. leniusculus experiencing a short period of rapid growth (Hogger 1986).

Pacifastacus leniusculus is both a fast growing and long-lived species. It’s known as one of the fastest growing species of temperate zone crayfish (Holdich and Lowery 1988), and in general, the highest growth rates are associated with populations which have recently invaded an unexploited habitat (Hogger 1986). These rapid growth rates subside as populations establish and densities surge, presumably because of increased competition for food and space (Hogger 1986). Their potential for rapid growth has made them the focus of both aquaculture productions and commercial fisheries in several countries (Westman 1973; Furst 1977; McGriff 1983; Goddard and Hogger 1986; Lowery and Holdich 1988). Hogger (1984) found that individuals from a population of P. leniusculus in southern England had the potential to grow up to 62 mm CL in as few as three years when grown in ideal conditions.  Overall, the Signal Crayfish may survive up to 9 years or more when living in the wild (Goldman and Rundquist 1977).

Means of Introduction: Potential introduction pathways for P. leniusculus include stocking for harvest, the release of crayfish used as live bait, and stocking as an additional food source for fish (Lowery and Holdich 1988; Lodge et al. 2000). The Signal Crayfish is known to be introduced to the Truckee River and Lake Tahoe, NV., as early as 1895 and 1909, respectively (La Rivers 1962; Abrahamsson and Goldman 1970), and records show that it was stocked in the Sacramento River and coastal waterways of California as early as 1912 (Riegel 1959). In both regions, P. leniusculus was intentionally stocked to enhance the forage available to fish (both native and nonnative), and to provide a harvest fishery for residents (La Rivers 1962; Abrahamsson and Goldman 1970; Lowery and Holdich 1988, lodge et al. 2000).

Status: Human mediated introductions have allowed Signal Crayfish (P. l. leniusculus, P. l. klamathensis, and P. l. trowbridgii) to expand their distributions into a variety of habitats ranging from the warm coastal waterways of the Sacramento River Delta to the sub-alpine waters of Lake Tahoe and Donner in California (Holdich and Lowery 1988; Larson et al. 2012; Larson and Williams 2015). The Signal Crayfish (Pacfastacus l. leniusculus) has been introduced to and is established in regions of Oregon, Washington, California, Nevada, Utah, and British Columbia. The Columbia River Signal Crayfish (Pacifastacus l. trowbridgii) is also known to be established in regions outside of its native range in Oregon, Washington, California and Nevada (Taylor et al. 2007). Based on the invasion history, it is likely that the distributions of P. leniusculus subspecies have been augmented within their own proposed native ranges through additional stockings (Larson and Olden 2011). For example, Signal Crayfish in Crater Lake, OR., were historically restricted from entering the waterbody, but later stocked there in 1915 to provide food for game fish previously introduced to the lake (Lowery and Holdich 1988; Girdner 2018).  Pacifastacus leniusculus is now so abundant in California it supports a robust commercial fishery in the Sacramento River Delta (McGriff 1983).

Impact of Introduction: Numerous crayfish species introduced outside of their native ranges have been injurious to aquatic ecosystems and valuable fisheries throughout the world (McCarthy et al. 2006; Larson and Olden 2011). The presumed extinction of the Sooty Crayfish (P. nigrescens) is attributed to the introduction of the Signal Crayfish, as well as the impacts associated with the urbanization of the Sacramento River (Bouchard 1977; Larson and Williams 2015). Currently, the Shasta Crayfish (P. fortis), is threatened by the introduction of P. leniusculus and the Virile Crayfish (0rconectes virilis), which has led both directly and indirectly to its recent range restriction (Lowery and Holdich 1988; Light et al. 1995). Signal Crayfish are also known to prey upon the eggs of game fish, such as the Atlantic Salmon (Salmo salar), which can contribute to declines in fish populations (Findlay et al. 2015). Pacifastacus leniusculus may have led to the collapse of a federally listed three-spined stickleback (Gasterosteus aculeatus) after it was introduced to Enos Lake in British Columbia (Behm et al. 2010).

The Mazama Newt (Taricha granulosa mazamae), which is endemic to Crater Lake, Oregon, is greatly threatened by the presence of the nonnative Signal Crayfish (Girdner 2018). Although newts remained in uninvaded regions of the lake, they were nearly absent from areas occupied by the crayfish. Mesocosm experiments revealed that P. leniusculus prey directly on newts, displace newts from cover, and have the potential to alter their overall behavior. Areas inhabited by the introduced crayfish also experienced dramatic decreases in benthic macroinvertebrate diversity (Girdner 2018). Crawford et al. (2006) found that the total number of invertebrates was significantly lower in sites where Signal Crayfish were present. Moorhouse et al. (2014) observed an inverse relationship between P. leniusculus and macroinvertebrate abundance and taxon richness.

The spread of American crayfish species in Europe during the 19th, 20th, and 21st century is closely associated with the spread of the crayfish plague (Holdich et al. 2009). Signal Crayfish serve as carriers of the crayfish plague, which is caused by a fungus-like organism (Aphanomyces astaci) (Cerenius et al. 1988). While P. leniusculus are highly resistant to the illness, Asiatic, Australian, and European crayfish are very susceptible to the plague’s ill effects (Unestam 1969). Although it was not introduced until the mid-1900’s, the Signal Crayfish is thought to be vector for spreading the plague (Lowery and Holdich 1988), and introductions of P. leniusculus to new regions in Europe are believed to contribute to the infection of new drainages (Cerenius et al. 1988).

Though uncommon, Signal Crayfish have been documented burrowing in river banks (Guan 2010). In the Great River Ouse, England, burrows were constructed at high densities (5.6 burrows per meter length), which increased the erosion of the river banks (Guan 2010).

Remarks: The Signal Crayfish’s ability to exploit a variety of habitats and conditions has enabled it to become established in a wide range of environments throughout Europe (Lowery and Holdich 1988). During the late 19th and early 20th centuries, crayfish in many European countries were decimated by the fungal infection, Aphanomyces astaci, also known as the crayfish plague (Alderman et al. 1996).  The collapse of Noble Crayfish (Astacus astacus) populations in the late 19th and early 20th century greatly impacted European countries, such as Sweden, where crayfish supported significant commercial fisheries (Lowery and Holdich 1988). Beginning in the 1960’s, Pacifastacus leniusculus were imported to Sweden and introduced throughout Europe in an attempt to establish a plague resistant species that would supplement stocks decimated by the crayfish plague. The Signal Crayfish is now widespread throughout Europe where it supports commercial fisheries but threatens endemic species such as the Noble Crayfish (Astacus astacus) through competition and disease (Lowery and Holdich 1988; Ibbotson and Furse 1995, Holdich et al. 2009).

References: (click for full references)

Abrahamsson, S.A.A., and C.R. Goldman. 1970. Distribution, density and production of the crayfish Pacifastacus leniusculus Dana in Lake Tahoe, California - Nevada. Oikos 21:83-91.

Agerberg, A., and H. Jansson. 1995. Allozymic comparisons between three subspecies of the freshwater crayfish Pacifastacus leniusculus (Dana), and between populations introduced to Sweden. Hereditas 122(1):33-39. https://doi.org/10.1111/j.1601-5223.1995.00033.x.

Alderman, D. J. 1996. Geographical spread of bacterial and fungal diseases of Crustaceans. Reviews of the Science and Technology Office for International Epizootiology 15:603-632.

Avault, J.W., Jr. 1973. Crayfish farming in the United States. Freshwater Crayfish 1:240-250.

Behm, J.E., A.R. Ives, and J.W. Boughman. 2010. Breakdown in postmating isolation and the collapse of a species pair through hybridization. The American Naturalist 175(1):11-26. https://doi.org/10.1086/648559.

Bouchard, R.W. 1977. Distribution, systematic status and ecological notes on five poorly known species of crayfish in western North America (Decapoda: Astacidae and Cambaridae). Freshwater Crayfish 3:409-423.

Capurro, M., L. Galli, M. Mori, S. Salvidio, and A. Arillo. 2007. The signal crayfish, Pacifastacus leniusculus (Dana, 1852)[Crustacea: Decapoda: Astacidae], in the Brugneto Lake (Liguria, NW Italy). The beginning of the invasion of the river Po watershed. Aquatic Invasions 2(1):17-24. http://www.aquaticinvasions.net/2007/AI_2007_2_1_Capurro_etal.pdf.

Cerenius, L., Soderhall, K., Persson, M. and Ajaxon, R. 1988. The crayfish plague fungus Aphanomyces astaci - diagnosis, isolation and pathobiology. Freshwater Crayfish 7:131-144.

Crawford, L., W.E. Yeomans, and C.E. Adams. 2006. The impact of introduced signal crayfish Pacifastacus leniusculus on stream invertebrate communities. Aquatic Conservation 16(611-626):611-626. https://doi.org/10.1002/aqc.761

Findlay, J., F. Findlay, W. Riley, M. Lucas. 2015. Signal crayfish (Pacifastacus leniusculus) predation upon Atlantic salmon (Salmo salar) eggs. Aquatic Conservation: Marine and Freshwater Ecosystems 25:250-258.

Flint. 1975. Growth in a population of crayfish Pacifastacus leniusculus from a subalpine lacustrine environment. Journal of the Fisheries Research Board of Canada 32(12):2443-2440. https://doi.org/10.1139/f75-280.

Furst, M. 1977. Introduction of Pacifastacus leniusculus (Dana) into Sweden: methods, results, and management. Freshwater Crayfish 3:229-248.

Girdner, S.F., A.M. Ray, M.W. Buktenica, D.K. Hering, J.A. Mack, and J.W. Umek. 2018. Replacement of a unique population of newts (Taricha granulosa mazamae) by introduced signal crayfish (Pacifastacus leniusculus) in Crater Lake, Oregon. Biological Invasions 20(3):721-740. https://link.springer.com/article/10.1007/s10530-017-1570-6/fulltext.html.

Goddard, J.S., and J.B. Hogger. 1986. The current status and distribution of freshwater crayfish in Britain. Field Studies 6(3):383-396.

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Author: Procopio, J.

Revision Date: 9/14/2021

Citation Information:
Procopio, J., 2024, Pacifastacus leniusculus (Dana, 1852): U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, https://nas.er.usgs.gov/queries/FactSheet.aspx?speciesID=200, Revision Date: 9/14/2021, Access Date: 6/18/2024

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.


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Citation information: U.S. Geological Survey. [2024]. Nonindigenous Aquatic Species Database. Gainesville, Florida. Accessed [6/18/2024].

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