Pacifastacus fortis
CR

Pacifastacus fortis

Declining

Photo: Wikimedia Commons (CC) via https://en.wikipedia.org/wiki/Pacifastacus_fortis

Overview

Pacifastacus fortis is an endangered crayfish species endemic to Shasta County, California, where it is found and first described in 1914, only in isolated spots along the Pit River and Fall River Mills. It is estimated that there are a total of roughly 4000 of the species still alive today. The exact subpopulations for the Shasta crayfish were discovered in 2004 through a genetic study that determined three different genetic clusters: Crystal Lake, the Big Lake group, and Thousand Springs.

Pacifastacus fortis faces severe population decline primarily due to habitat degradation from agricultural runoff and urban development in its limited California range. Competition and disease transmission from introduced crayfish species, particularly the signal crayfish, pose additional threats to remaining populations. Water diversions and drought conditions have further reduced suitable habitat availability in the species' already restricted distribution.

Threat summary

Habitat

This freshwater crayfish inhabits cool, clear streams and rivers in the Sacramento-San Joaquin river system of California. It requires well-oxygenated waters with rocky substrates and riparian vegetation cover.

Rocky areas· major

Conservation measures underway

Habitat & natural process restorationSpecies managementSpecies recoveryLegislation

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Frequently asked questions

Why is Pacifastacus fortis classified as Critically Endangered?
Pacifastacus fortis is classified as Critically Endangered — facing an extremely high risk of extinction in the wild — because population sizes are very small, declining sharply, or restricted to a tiny range. Pacifastacus fortis faces severe population decline primarily due to habitat degradation from agricultural runoff and urban development in its limited California range. Competition and disease transmission from introduced crayfish species, particularly the signal crayfish, pose additional threats to remaining populations. Water diversions and drought conditions have further reduced suitable habitat availability in the species' already restricted distribution.
Where does Pacifastacus fortis live?
Pacifastacus fortis occurs in United States. Country-level distribution data is sourced from the IUCN Red List and cross-referenced with GBIF occurrences.
What are the main threats to Pacifastacus fortis?
The main threats to Pacifastacus fortis are 1.1, 3.3, 5.3, and 7.2. The full IUCN-classified threat record for this species is detailed on the species page.

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