Pacifastacus fortis is an endangered crayfish

Crayfish

Crayfish, crawfish, or crawdads – members of the superfamilies Astacoidea and Parastacoidea – are freshwater crustaceans resembling small lobsters, to which they are related...

 species endemic to Shasta County

Shasta County, California

Shasta County is a county located in the northern portion of the U.S. state of California. The county occupies the northern reaches of the Sacramento Valley, with portions extending into the southern reaches of the Cascade Range. As of the 2010 census, the population was 177,223, up from 163,256...

, California

California

California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

, where it is found only in isolated spots on the Pit River

Pit River

The Pit River is a major river draining from northeastern California into the state's Central Valley. The Pit, the Klamath and the Columbia are the only three rivers in the U.S...

 and Fall River Mills.

Description and ecology

P. fortis is thick and stocky, with relatively heavy chelae

Chela (organ)

A chela is a pincer-like organ terminating certain limbs of some arthropods. The name comes from Greek through New Latin . The plural form is chelae. Legs bearing a chela are called chelipeds. Another name is claw because most chelae are curved and have a sharp point like a claw....

. It is usually dark brown dorsally with bright orange areas on its underside, but there is also a brilliant blue color morph. It is about three inches long. It lives in cold, clear, rocky areas of the mountain rivers, and feeds on the slime coating the rocks. The animal requires a constant, steady, and untainted flow of fresh water to survive.

Conservation

Pacifastacus fortis is listed as a critically endangered

Critically endangered

Version 2010.3 of the IUCN Red List of Threatened Species identified 3744 Critically Endangered species, subspecies and varieties, stocks and subpopulations.Critically Endangered by kingdom:*1993 Animalia*2 Fungi*1745 Plantae*4 Protista-References:...

 species on the IUCN Red List

IUCN Red List

The IUCN Red List of Threatened Species , founded in 1963, is the world's most comprehensive inventory of the global conservation status of biological species. The International Union for Conservation of Nature is the world's main authority on the conservation status of species...

, and an endangered species

Endangered species

An endangered species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters...

 under the Endangered Species Act

Endangered Species Act

The Endangered Species Act of 1973 is one of the dozens of United States environmental laws passed in the 1970s. Signed into law by President Richard Nixon on December 28, 1973, it was designed to protect critically imperiled species from extinction as a "consequence of economic growth and...

. It has always had a very small native range, and that range has been significantly fragmented by such human activities as damming, mining, and agriculture. The signal crayfish

Signal crayfish

The signal crayfish, Pacifastacus leniusculus, is a North American species of crayfish. It was introduced to Europe in the 1960s to supplement the Scandinavian Astacus astacus fisheries, which were being damaged by crayfish plague, but the imports turned out to be a carrier of that disease...

, a recently introduced species

Introduced species

An introduced species — or neozoon, alien, exotic, non-indigenous, or non-native species, or simply an introduction, is a species living outside its indigenous or native distributional range, and has arrived in an ecosystem or plant community by human activity, either deliberate or accidental...

, has outcompeted P. fortis in much of its range. The Pit River Fish Hatchery was closed to protect this species.