Pacifastacus leniusculus (Dana, 1852)

Common Name: Signal Crayfish

Synonyms and Other Names:

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Dark brown in color with a distinctive turquoise or white patch at the base of each claw.  Adults may have a blue tinge. Compared to other crayfish, Signal Crayfish are much smoother on all surfaces especially the claw.

Size: 12-16 cm rostrum to telson

Native Range: North America between the Pacific Ocean and the Rocky Mountains, ranging from British Columbia south to Central California.

This species is not currently in the Great Lakes region but may be elsewhere in the US. See the point map for details.

Table 1. States/provinces with nonindigenous occurrences, the earliest and latest observations in each state/province, 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.

State/ProvinceFirst 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 2/24/2024

† Populations may not be currently present.

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

Ecology: The Signal Crayfish has broad temperature and salinity tolerances and can occupy a wide range of habitats. They live in small streams, large rivers, ponds, and lakes. They prefer streams and rivers with cool water and rocky substrate (Schuster et al., 2010). Because of their tolerance to higher salinity and temperatures, they are commonly cultured in the Western United States.

They have a broad and flexible diet that includes different trophic levels. As juveniles they typically feed on aquatic insects, shifting towards a more herbivorous diet as adults (Lewis, 2002). They are also known to cannibalize other Signal Crayfish throughout their life history.

Signal Crayfish mate in October. Egg incubation lasts from approximately 160 to 280 days with hatching occurring between March and July  depending on temperature (GISD, 2005). They may live for as long as 20 years, and in some low density populations may grow as large as 95 mm carapace length (GISD, 2005). Newly hatched crayfish stay with their mother for three molts before becoming independent (Lewis, 2002).

Pacifastacus leniusculus is resistant to crayfish plague, but they do carry the disease (Schuster et al., 2010). They were first introduced to Sweden and Finland between 1967 and 1969 in an effort to bolster crayfish populations, however they contributed to the spread of the crayfish plague and therefore the further decline of native Noble Crayfish populations throughout Europe (Astacus astacus) (Johnsen and Taugbøl, 2010).

Means of Introduction: Means of Introduction: Pacifastacus leniusculus has a High probability of introduction to the Great Lakes (Confidence level: Moderate).

    Potential pathway(s) of introduction: Unauthorized Intentional Release
    Signal crayfish are a popular aquarium and bait species because of their hardiness and fast growth rates. They are readily available from online aquarium retailers. There are no specific regulations preventing the purchase of this species in the Great Lakes Region. They are also a popular species for commercial culture, however they are not currently cultured in the Great Lakes Region.

Status: Signal Crayfish are native to the Western United States. They have been introduced to Oregon, Utah, Idaho, Nevada, and Washington (Schuster et al., 2010). However, their introduced range has not spread east of the continental divide in North America. They have a broad range in Europe where they were originally introduced to improve crayfish populations (Holdich et al., 2009). They contributed to declines in native crayfish populations, particularly the Noble Crayfish (Astacus astacus) through the introduction of the crayfish plague as well as direct competition (Souty-Grosset, 2006). They are commonly raised for bait and human consumption in the United States, however this activity is far outside of the Great Lakes Region.

Pacifastacus leniusculus has a High probability of establishment if introduced to the Great Lakes (Confidence level: High).
        Signal Crayfish are tolerant to broad temperature and salinity ranges (Fofonoff et al., 2003). Their native and introduced range has a very similar climate to the Great Lakes region (Sanders et al., 2014). P. leniusculus has a broad, flexible, polytrophic diet (Lewis, 2002), and they have been demonstrated to outcompete native species in their introduced range. Schuster et al. (2010) describes Signal Crayfish as an R-selected species, typically their egg numbers range from 200-400 with some individuals laying as many as 500 eggs per breeding event (GISD, 2005). Signal Crayfish occupy a wide range of habitats including small streams, large rivers, and lakes (GISD, 2005), all of which are easily found and readily available in the Great Lakes Region.

Great Lakes Impacts:
Summary of species impacts derived from literature review. Click on an icon to find out more...


Pacifastacus leniusculus has the potential for High environmental impact if introduced to the Great Lakes.
    Signal Crayfish are a known carrier of Crayfish plague, a parasite listed as one of the top 100 worst invaders by the International Union for Conservation of Nature (Lowe et al., 2000). Crayfish Plague spread by Signal Crayfish was a major contributor to declines in native Noble Crayfish populations throughout Europe (Alderman, 1996). P. leniusculus are opportunistic polytrophic feeders which affect populations of fish, macroinvertebrates, and aquatic plants through competition and predation (Guan & Wiles 1997; Nyström 1999; Lewis 2002). Griffiths et al. (2004) found that Signal Crayfish outcompeted Atlantic Salmon for shelter in an artificial test arena, possibly indicating that their presence might make sport fish more vulnerable to predation. Although they are not known to burrow in their native range, P. leniusculus construct burrows that contribute to bank erosion and collapse in their introduced range (GISD, 2005).

Pacifastacus leniusculus has the potential for moderate Socio-Economic impact if introduced to the Great Lakes.
Signal Crayfish have not been reported to present any hazards to human health or infrastructure. They have not been shown to diminish water quality or inhibit recreational use significantly. However, their presence may affect Atlantic Salmon fisheries through shelter competition (Griffiths et al., 2004) and consumption of eggs (Findlay et al. 2014). Signal Crayfish burrows reach a high density which could potentially reduce the perceived aesthetic of the areas it inhabits.
Pacifastacus leniusculus has the potential for high beneficial impact if introduced to the Great Lakes.
    Signal Crayfish are a popular species for bait as well as human consumption. They are commonly used to control nuisance vegetation in aquaculture ponds (GISD, 2005). They are commercially valuable both for aquaculture and as a fishery, they are commercially harvested in the western US as well as in Europe (GISD, 2005).

Management: Regulations (pertaining to the Great Lakes region)
        There are no known regulations specific to this species. However, Pennsylvania restricts the sale, possession, introduction and transportation of all crayfish species; Wisconsin  prohibits all non-native crayfish; and Minnesota prohibits the importation of all crayfish into the state. Note: Check federal, state/provincial, and local regulations for the most up-to-date information

    Northern Pike (Esox lucius), Atlantic Salmon (Salmo salar), and Brown Trout (Salmo trutta) have all been found to consume Signal Crayfish in their introduced range. Restricting harvest of these species in areas where P. leniusculus has been introduced may reduce their population. However, fish predation has not been found to effectively limit Signal Crayfish populations (Freeman et al., 2010).
Intensive trapping is a common method used to control crayfish (Reeve, 2004; Moorhouse et al., 2013; Peay, 2001) . Kick sampling, although much more labor intensive than trapping, captures more crayfish than trapping (Peay, 2001). While it may not be effective at eradicating Signal Crayfish, physical removal of Signal Crayfish has been shown to improve macroinvertebrate abundance and species richness (Moorhouse et al., 2014).
BETAMAX VET ® was used in combination with pond drainage to eradicate P. leniusculus from the Dammane area in Norway; however, this treatment is only feasible on small and isolated bodies of water (Sandodden and Johnsen, 2010).
    Emamectin benzoate is effective against arthropod pests with little reported negative impact on non-target species (Freeman et al., 2010).

References (click for full reference list)

Author: Boucher, N., A. Elgin

Contributing Agencies:

Revision Date: 3/14/2019

Citation for this information:
Boucher, N., A. Elgin, 2024, Pacifastacus leniusculus (Dana, 1852): U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI,, Revision Date: 3/14/2019, Access Date: 2/24/2024

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.