Shasta Crayfish

Pacifastacus fortis

Photo of Shasta Crayfish
Photo Credit: Koen G. H. Breedveld / Spring Rivers Ecological Sciences LLC

Shasta Crayfish

Basic Species Information

STATUS

Endangered. This species is in danger of extinction throughout all or a significant portion of its range.

DESCRIPTION

The Shasta crayfish is a small- to medium-sized crayfish. The total length of its carapace (shell covering the back over the walking legs) may reach 2.5 to 5 cm (1-2 inches.) Color is variable and may range from dark brownish green to dark brown on the topside and bright orange on the underside. Members of the Fall River population are dark orange-brown on the topside and bright red on the underside, especially on the chelae (pinchers). These colors provide camouflage for the crayfish among the volcanic rubble substrates of its habitat.

Males and females can easily be distinguished because the males have narrower abdomens and larger chelae than the females. The first two pair of swimmerets (tiny swimming legs) of the males are hard and modified for sperm transfer to the female during mating. These notable sexual characteristics can be seen in young larvae that are less than 1 cm (0.4 inch) long (total carapace length).

Inactive until after dark, the Shasta crayfish stays mostly in one place until mating season. They live an average of 10 to 15 years.

FOOD SOURCES

The food preferences and nutritional requirements of the species are unknown. It is believed that the primary foods are periphyton (plankton that live attached to rooted aquatic plants) and small invertebrates, such as snails. The crayfish have been observed feeding on snails, aquatic vegetation and organic debris.

HABITAT

They live in cool, clear, spring-fed lakes, rivers and streams, usually at or near a spring inflow source, where waters show little annual fluctuation in temperature and remain cool during the summer. Most are found in still and slow to moderate flowing waters. The most important habitat requirement appears to be the presence of adequate volcanic rock rubble to provide escape cover from predators.

MATING

It takes five years for the Shasta crayfish to reach sexual maturity.

Mating occurs in October or November. The male deposits a capsule containing sperm on the underside of the female, near her genital opening. Soon, the female lays 10 to70 eggs, which she fertilizes with the sperm and then attaches to the underside of her abdomen or tail. In spring, the eggs hatch into immature larva. These molt into miniatures of the adults. After they molt again, they gradually become free-living.

RANGE

The Shasta Crayfish is an endangered species native to northeast California There are only seven remaining populations of the Shasta crayfish left and are found only in Shasta County, California, in the Pit River drainage and two tributary systems, Fall River and Hat Creek drainages.

PREDATORS

Many native and introduced fish, amphibians, reptiles and mammals found in the Pit River region are known to prey on crayfish, although predation on Shasta crayfish has not been documented.

THREATS

This species is endangered by habitat loss from water diversions, predation, and competition with the exotic signal crayfish (Pacifastacus leniusculus) and other species. Two entire populations have been extirpated since 1978.

The Signal crayfish threatens to take over Shasta crayfish habitat in part because they mature in only 2 years and produce more than twice as many eggs per year.