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What the sources say

Signal CrayfishPacifastacus leniusculus

Every figure, record and mechanism on the Signal Crayfish profile was written from a source, and this is the working table behind it: 47 claims checked word for word against these sources. The left column is what the page says. The right column is the source's own words, copied, not paraphrased; a ... marks a cut and[brackets] an insertion. Open any source and check it yourself.

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Source
01

U.S. Fish and Wildlife Service

Signal Crayfish (Pacifastacus leniusculus) Ecological Risk Screening Summary. U.S. Fish and Wildlife Service.

The page saysA plague-resistant crayfish brought to Europe to supplement stocks the plague decimated
The source saysimported to Sweden and introduced throughout Europe in an attempt to establish a plague resistant species that would supplement stocks decimated by the crayfish plague.Note: tagline, first half. Quoted in the FWS summary from Procopio (2021). Carrier half has its own claim.
The page saysa carrier of the disease itself
The source saysSignal Crayfish serve as carriers of the crayfish plague, which is caused by a fungus-like organism ( Aphanomyces astaci )Note: tagline, second half. Quoted in the FWS summary from Procopio (2021).
The page saysHighly resistant to the crayfish plague
The source saysWhile P. leniusculus are highly resistant to the illnessNote: stats.superpower. Quoted in the FWS summary from Procopio (2021).
The page saysSmall streams, large rivers and natural lakes
The source saysP. leniusculus can be found in a variety of habitats, from small streams to large rivers and natural lakes.Note: stats.habitat. Quoted in the FWS summary from Houghton and Allen (2014).
The page saysnative to the Columbia River Basin and Oregon's coast
The source saysthe 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 boundaryNote: stats.habitat. Procopio (2021), quoted in the FWS summary; replaces Houghton and Allen's (2014) British Columbia to central California range, which the same document's more recent sources show includes introduced populations (California, Nevada, Utah, Montana).
The page saysmany European countries
The source saysIn the 1960s , P. leniusculus was introduced into Europe and now occurs in many countries from the UK and France in the west, to Russia in the east.Note: stats.habitat. Quoted in the FWS summary from Houghton and Allen (2014).
The page saysBeginning in the 1960s, signal crayfish were imported to Sweden and introduced across Europe to build a plague-resistant stock that would supplement the stocks the plague had decimated.
The source saysBeginning 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.Note: Quoted in the FWS summary from Procopio (2021).
The page saysa disease caused by a fungus-like organism called Aphanomyces astaci
The source saysthe crayfish plague, which is caused by a fungus-like organism ( Aphanomyces astaci )Note: Quoted in the FWS summary from Procopio (2021).
The page saysIts spread across Europe has helped the plague spread too, decimating native crayfish populations.
The source saysThe spread of P. leniusculus throughout Europe has enabled Aphanomyces astaci , the crayfish plague, to spread as well, decimating native crayfish populationsNote: Quoted in the FWS summary from Houghton and Allen (2014), who cite Holdich et al. (2009).
The page saysThe signal crayfish is highly resistant to the plague. Asiatic, Australian and European crayfish are very susceptible to its ill effects.
The source saysWhile P. leniusculus are highly resistant to the illness, Asiatic, Australian, and European crayfish are very susceptible to the plague’s ill effectsNote: Quoted in the FWS summary from Procopio (2021), who cites Unestam (1969).
The page saysThe average adult has a carapace, the hard shell over its head and chest, 50 to 70 mm long.
The source saysThe average Signal Crayfish attains a carapace length (CL) of 50-70 mm (Capurro et al. 2007).Note: Quoted in the FWS summary from Procopio (2021). The gloss of carapace is a definition, not a source claim.
The page saysIn the wild a signal crayfish may survive up to 9 years or more
The source saysthe Signal Crayfish may survive up to 9 years or more when living in the wild (Goldman and Rundquist 1977).Note: Quoted in the FWS summary from Procopio (2021), citing Goldman and Rundquist (1977).
The page saysThe back is typically brownish-tan.
The source saysThe dorsal surface of Signal Crayfish is typically brownish-tan in coloration.Note: Quoted in the FWS summary from Procopio (2021); dorsal surface glossed as back.
The page saysThe claws are bright red underneath, and a white or turquoise patch sits at the base of each claw joint.
The source saysA 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 CrayfishNote: Quoted in the FWS summary from Procopio (2021).
The page saysit may eat more animal than plant material when it can
The source saysalthough more animal than plant material may be consumed if availableNote: Quoted in the FWS summary from GISD (2023).
The page saysIn crowded populations, competition and cannibalism can greatly affect survival.
The source saysCompetition and cannibalism can greatly affect survival in dense populations.Note: Quoted in the FWS summary from GISD (2023); the quote follows survivorship to age 2.
The page saysFemales carry their eggs through the winter
The source saysfemales carry the eggs throughout the winterNote: Procopio (2021), quoted in the FWS summary
The page saysusually 200 to 400
The source saysEgg numbers usually range from 200 to 400Note: Quoted in the FWS summary from GISD (2023).
The page saysAt home it is native to the Columbia River Basin, whose tributaries reach into Washington, Oregon, Idaho and British Columbia, and south along Oregon's coast to the Klamath River.
The source saysthe 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 boundaryNote: Procopio (2021), quoted in the FWS summary.
The page saystolerates water temperatures up to 33°C
The source saysIts ability to tolerate water temperatures up to 33°C has allowed it to prosper in many environments.Note: Quoted in the FWS summary from Houghton and Allen (2014).
The page saysIn Europe it now occurs in many countries, from the UK and France in the west to Russia in the east, and from Norway, Sweden and Finland in the north to the Iberian Peninsula in the south.
The source saysnow occurs in many countries from the UK and France in the west, to Russia in the east. ... the northern extent is Norway, Sweden and Finland, while the southern extent is the Iberian Peninsula.Note: Quoted in the FWS summary from Houghton and Allen (2014).
The page saysIt has also been introduced to Japan.
The source says[Introduced to] Hokkaido, Fukushima, Shiga, Nagano, Tochigi and Chiba Prefs [Japan].Note: Quoted in the FWS summary from NIES (2023).
The page saysAt sites with high crayfish density, benthic macroinvertebrate biomass, the weight of bottom-dwelling animals without backbones, was 99% lower than at low-density sites.
The source saysAt high crayfish density sites, benthic macroinvertebrate biomass was 99% lower, and taxa richness was 50% lower than at low crayfish areas.Note: Scordo (2023), quoted in the FWS summary; Crater Lake is in Oregon per the FWS text (Crater Lake, OR.). The gloss is a definition.
The page saysWild signal crayfish may survive up to 9 years or more.
The source saysthe Signal Crayfish may survive up to 9 years or more when living in the wild
The page saysother estimates say it may be as long as 20 years
The source saysother estimates state that it may be as long as 20 yearsNote: GISD (2023), quoted in the FWS summary
The page saysEstimates using lipofuscin, a pigment that builds up with age, suggest some individuals can live 16 years
The source saysBased on the use of the lipofuschin technique it has been estimated that some individuals can live 16 yearsNote: GISD (2023), quoted in the FWS summary; source spells it lipofuschin. The pigment gloss is a definition.
The page saysUsually 200 to 400, although some females of 66 mm carapace length have been reported with over 500.
The source saysEgg numbers usually range from 200 to 400, although some individuals of 66mm CL have been reported as having over 500 eggs.Note: GISD (2023), quoted in the FWS summary
The page saysThe eggs take 166 to 280 days to hatch.
The source saysEgg incubation time ranges from 166 to 280 days.Note: GISD (2023), quoted in the FWS summary
The page saysThey are known to occur in brackish water along the Pacific Coast at salinities as high as 20 ppt
The source saysIt is also known to occur in brackish waters along the Pacific Coast in salinities as high as 20 ppt (Riegel, 1959).Note: Houghton and Allen (2014), quoted in the FWS summary
The page saysa lab study found they can occupy water of about 26 ppt, 75% seawater, for several days
The source saysWheatly & 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.Note: Procopio (2021), quoted in the FWS summary
The page saysusually 200 to 400 of them
The source saysEgg numbers usually range from 200 to 400Note: GISD (2023), quoted in the FWS summary
The page sayscarries the plague itself
The source saysSignal Crayfish serve as carriers of the crayfish plagueNote: Procopio (2021), quoted in the FWS summary
The page saysIt lives in everything from small streams to large rivers and natural lakes
The source saysP. leniusculus can be found in a variety of habitats, from small streams to large rivers and natural lakes.Note: Houghton and Allen (2014), quoted in the FWS summary
The page saysPeople have also established it in new waters in Oregon, Washington, California, Nevada, Utah
The source sayshas been introduced to and is established in regions of Oregon, Washington, California, Nevada, [and] UtahNote: Procopio (2021), quoted in the FWS summary. "regions of" kept as "new waters": the native range covers parts of Oregon and Washington, and the 2025 summary notes the subspecies ranges are contested
The page saysand Montana
The source saysUSGS (2025) reports nonnative introductions of Pacifastacus leniusculus in Montana that resulted in an established populationNote: body
The page saysJapan
The source says[Introduced to] Hokkaido, Fukushima, Shiga, Nagano, Tochigi and Chiba Prefs [Japan].Note: stats.habitat; NIES (2023), quoted in the FWS summary
The page saysCrater Lake in Oregon had no signal crayfish until they were stocked there in 1915 to feed game fish.
The source saysSignal 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 lakeNote: Procopio (2021), quoted in the FWS summary
The page saysintroduced to new waters in the western US
The source sayshas been introduced to and is established in regions of Oregon, Washington, California, Nevada, [and] UtahNote: stats.habitat; Procopio (2021), quoted in the FWS summary
The page saysA white or turquoise patch marks the base of each claw joint of a signal crayfish, against claws that are bright red underneath.
The source saysA 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 CrayfishNote: vibe.reason; Quoted in the FWS summary from Procopio (2021).

Source
02

Alaska Center for Conservation Science

Pacifastacus leniusculus biological summary. Alaska Center for Conservation Science.

The page saysMales can reach 16 cm long, while females reach a maximum of 12 cm.
The source saysMale crayfish can reach a length of 16 cm, while females can only achieve a maximum size of 12 cm.Note: Also in the FWS summary, from Houghton and Allen (2014)
The page saysAge at maturity varies from 1 to 3 years.
The source saysAge at maturity varies from 1 to 3 years
The page saysa life expectancy of up to 20 years is possible
The source saysa life expectancy of up to 20 years is possible

Source
03

Smithsonian Environmental Research Center, NEMESIS

Pacifastacus leniusculus species summary. Smithsonian Environmental Research Center, NEMESIS.

The page saysOmnivore: aquatic plants, freshwater invertebrates and carrion
The source saysaquatic plants, freshwater invertebrates, carrionNote: stats.diet; Trophic Status: Omnivore on the same page
The page saysaquatic plants, freshwater invertebrates and carrion
The source saysaquatic plants, freshwater invertebrates, carrion

Source
04

Sbragaglia & Breithaupt 2021

Sbragaglia & Breithaupt (2021). Daily activity rhythms, chronotypes, and risk-taking behavior in the signal crayfish. Current Zoology.

The page saysIt is a nocturnal species
The source saysprevious studies showed that the signal crayfish is a nocturnal species

Source
05

Schuster, Taylor & Cordeiro 2010

Schuster, Taylor & Cordeiro (2010). Pacifastacus leniusculus. The IUCN Red List of Threatened Species 2010: e.T153648A4526314.

The page saysLeast Concern
The source saysIUCN Red List category: Least Concern (LC).Note: stats.conservationStatus; assessed 2010, category read through GBIF's copy of the Red List
The page saysThe IUCN rates the species Least Concern.
The source saysIUCN Red List category: Least Concern (LC).Note: category read through GBIF's copy of the Red List; assessment year not stated in the body

How the table was made: a writer drafted the profile from these sources and logged each claim with its quote, a reviewer with nothing but this table checked every sentence said no more than its quote, and a script confirmed each quote appears word for word in the source. The method is in the site'sAbout page.