Pacifastacus fortis 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Arthropoda Malacostraca Decapoda Astacidae

Scientific Name: Pacifastacus fortis (Faxon, 1914)
Common Name(s):
English Placid Crayfish, Shasta Crayfish

Assessment Information [top]

Red List Category & Criteria: Critically Endangered B1ab(ii,iii,v) ver 3.1
Year Published: 2010
Date Assessed: 2010-06-01
Assessor(s): Johnson, D., Taylor, C.A., Schuster, G.A., Cordeiro, J. & Jones, T.
Reviewer(s): Collen, B. & Richman, N.
Contributor(s): Livingston, F., Livingston, F., Soulsby, A.-M., Batchelor, A., Dyer, E., Whitton, F., Milligan, H.T., Smith, J., Lutz, M.L., De Silva, R., McGuinness, S., Kasthala, G., Jopling, B., Sullivan, K. & Cryer, G.
Pacifastacus fortis has been assessed as Critically Endangered under criterion B1ab (ii,iii,v). This species has a very restricted range with an extent of occurrence of 13 km2, and a range that is severely fragmented by the presence of dams and invasive species. There is an ongoing decline in the quality of this species habitat as a result of dam construction, and invasive species continue to drive a decline in the number of mature individuals. Measures are urgently required to control the spread of invasive species towards the relict, subpopulations of this species.
Previously published Red List assessments:

Geographic Range [top]

Range Description:This species is known only from Shasta County, California, USA. It is more specifically known from isolated portions of the Pit River drainage. The current range is greatly reduced to much smaller and more isolated stream sections in the same watersheds (Millar 2004). This species has an estimated extent of occurrence of 13 km2.
Countries occurrence:
United States (California)
Additional data:
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:By 1990, Pacifastacus fortis was restricted to seven isolated localities, mostly in the headwaters of spring-fed tributaries of the Pit River. The Signal Crayfish (Pacifastacus leniusculus) had become established throughout much of the study area within 12 years. In one site P. leniusculus probably contributed to the precipitous decline of this species, from 2000 - 3000 in 1980 to about 370 (+ 135) in 1991 (Light et al. 1995). Relict distribution exist today but no evidence the species had a wider range during historic times (Eng and Daniels 1982).  Historically, distribution was more or less continuous throughout the Fall River, Hat Creek, and the segment of the Pit River that joins these drainages (Light et al. 1995).  It was described in 1898 from the Fall River at Fall River Mills and Hat Creek at Cassel with subsequent collections from the Fall River system in 1934, 1964, 1973-1974; with collections in 1975 from all three river systems (headwaters of the Fall River, Sucker Springs Creek on the Pit River, Crystal Lake on Hat Creek).  In 1978-1980 it was found in numerous locations in the Fall River system including the type locality as well as Sucker Springs Creek and the Pit River and in Crystal, Baum, and Rising River lakes on the Hat Creek system.  Resurveys in 1985-1986 found no major changes in distribution but noted a declining population in Crystal Lake occurring with a large population of introduced Pacifastacus leniusculus in only five years plus new observations in Eastman Lake at the Lava Creek overflow, the Fall River at the mouth of Spring Creek, and Tritton Reservoir. Most recently in 1990-1991, Light et al. (1995) found it in a total of 14 sites comprising seven noncontiguous subpopulations separated by dams, gradient barriers and many stream km; mostly in the same areas as historically but now isolated in patches rather than distributed continuously. The marginal locations (Fall River, Pit River mainstem near sucker Springs, and Baum Lake) have not yielded specimens since 1980, though these represented washdowns or strays from nearby populations.
Current Population Trend:Decreasing
Additional data:
Population severely fragmented:Yes

Habitat and Ecology [top]

Habitat and Ecology:Pacifastacus fortis prefers rocky, gravelly bottoms, usually volcanic rubble (Bouchard 1978). This species has been found in spring pools and slow to moderately flowing waters, and also in cold clear lakes with little annual fluctuation in temperature (Eng and Daniels 1982). It requires a constant, steady, and untainted flow of fresh water to survive (American Fisheries Society Endangered Species Committee 1996). Pacifastacus fortis grows to 90mm total length and females reach maturity at 5 years old (Millar 2004).
Generation Length (years):3-4

Threats [top]

Major Threat(s): This species faces a number of threats within its restricted range. This species has undergone significant habitat fragmentation as a result of water diversion and impoundments associated with 4 major hydroelectric dams (NatureServe 2009). Though range extent is still as it was historically, distribution is no longer continuous and the amount of occupied area within its range is significantly reduced (US Fish and Wildlife Service 1998, Light et al. 1995). The population of this species is now considered to be highly fragmented and split into isolated subpopulations as a result of dam construction (Millar 2004). Exotic and invasive species also pose another major threat to this species: it is likely that the decline of this species is linked to the spread of Pacifastacus leniusculus (Fetzner 2008) as well as Orconectes virilis, both of which have the characteristics typical of expanding populations (Daniels 1980, Light et al. 1995). Pacifastacus fortis is also subject to increased predation from non-native species such as muskrats, bullfrogs, and several species of introduced game fish (Millar 2004).

Conservation Actions [top]

Conservation Actions: Pacifastacus fortis received protection under the federal Endangered Species Act of 1973 (ESA) and has been classified as 'endangered' by the American Fisheries Society (Taylor et al. 2007). This species has been assigned a Global Heritage Status Rank of G1 by NatureServe (2009).

By installing and maintaining effective barriers in the river system, the plan to protect Pacifastacus fortis focuses on preventing the invasion of signal crayfish into the 20 remaining native subpopulations still free of the exotic species. When these subpopulations are stabilized, work will be done to remove signal crayfish from areas containing both crayfish species and additional barriers will also be installed. The plan requires government agencies to increase cooperative efforts with local landowners because much of the habitat is on private lands (Millar 2004).

Culverts at Spring Creek Road have been replaced using a design to prevent signal crayfish migration. The fish hatchery at Sucker Creek has been removed and a barrier installed. Restoration has been carried out on eroded areas. A recovery plan calls for future repairs on water impoundments to be done with imported boulders to improve Shasta Crayfish habitat instead of locally dredged materials. Removal or controls of muskrat populations throughout the watershed are to be undertaken (U.S. Fish and Wildlife Service 1998). Continued study of Shasta Crayfish ecology, and monitoring of Signal Crayfish are being carried out (Millar 2004).

Citation: Johnson, D., Taylor, C.A., Schuster, G.A., Cordeiro, J. & Jones, T. 2010. Pacifastacus fortis. The IUCN Red List of Threatened Species 2010: e.T15866A5246459. . Downloaded on 22 July 2018.
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