Shasta Crayfish

Pacifastacus fortis

Description

Also known as the placid crayfish, the Shasta crayfish is a small, decapod crustacean with a cara-pace length of 1-2 in (25-50 mm). Its color varies from dark green to greenish brown above, and the underside is bright orange or red, especially on the pincher-like claws. The often mottled coloration of the back provides excellent camouflage against stream and pool bottoms of volcanic rubble. Occasional individuals in isolated populations may be blue-green or blue on the top with a salmon-colored underside.

Adult Shasta crayfish are sexually dimorphic— males have narrower abdomens and larger pincers than females, and their first two pairs of swimming legs (swimmerets) are modified to transfer sperm to the female during mating.

Shasta crayfish are long-lived and slow-growing. Although age-class boundaries are often not very distinct, especially in older reproductive crayfish, the relative age of individual Shasta crayfish can be estimated from graphs based on data showing the relationship between age and size. It takes five years for a Shasta crayfish to reach sexual maturity at 1.06 in (2.7 cm). The largest Shasta crayfish found to date was a male, probably 10-15 years old, with a length of 2.31 in (5.9 cm).

Behavior

No research has determined the food preferences and nutritional requirements of Shasta cray-fish, but there have been a number of observations and hypotheses based on anatomy and observation in the field and laboratory. The failure to capture this species by using baited traps led to the premise that Shasta crayfish were either carnivores (meat eaters) or browsers (grazing on aquatic vegetation) rather than omnivorous scavengers (feeding on dead or decaying plants and animals) like signal crayfish, which are readily lured to baited traps. The structure of the mouthparts makes Shasta crayfish more efficient at scraping foods such as periphyton than the signal crayfish, which has a more generalized incisor surface. Shasta crayfish have been observed feeding on the small blackish-green snail, Fluminicola spp. In the field, Shasta crayfish were observed apparently feeding on snails, a strand of dead aquatic vegetation that was probably a filamentous green algae, and organic debris.

During night dives, researchers have observed Shasta crayfish on rocks with their mouthparts moving; this behavior suggests the crayfish are eating organisms attached to rocks (periphyton) and possibly snails; however, crayfish can also move their mouthparts as a sensory behavior when they are not feeding. Shasta crayfish have been observed moving their first walking legs (pereiopods) to their mouths or moving their claws to suggest feeding; although the crayfish were apparently grazing, no specific food items could be identified. Other observations have been made under artificial or experimental settings that suggest that Shasta crayfish feed on freshwater limpets and tubifex worms.

The primary food of Shasta crayfish appears to be the periphyton and invertebrates that are abundant in their native environment. Other potential food resources include trout, sucker, and sculpin eggs, which are seasonally abundant. Although some of the items Shasta crayfish will consume are known, nothing is known about their actual nutritional requirements. Some understanding of the nutritional requirements of Shasta crayfish is necessary before initiating long-term captive breeding programs.

It is active mainly after dark, unlike other related crayfish species. The Shasta crayfish is a solitary creature, except during mating season. As it grows it undergoes several molts, during which it sheds its carapace. It mates in late September and October after the last molt of the year. Females lay an average of 40 eggs in the fall, which hatch the following spring. Crayfish reach sexual maturity after five years.

Habitat

The Shasta crayfish prefers clear, spring-fed lakes, streams, and rivers, and usually congregates near spring flows where the water remains cool throughout the summer. Most colonies are found in still or slow currents over a base composed of cobbles and pebbles or of clean sand.

The past and present distribution of the Shasta crayfish is integrally tied to the geologic history of the Modoc Plateau, an immense lava field covering most of northeastern California. Because volcanic rock is porous, most rainfall percolates through the lava into the groundwater. Surface water is minimal, so rainfall from more than 50 mi (80.5 km) away and snowmelt from Lassen Peak, Medicine Lake Highlands, and other lesser peaks feed the groundwater that comes to the surface at contact springs, formed where permeable lava flows over-lie less-permeable material such as lakebed sediment, in the midsections of the Pit River drainage. The midsections of the Pit River drainage lie along the western margin of the Modoc Plateau geomorphic province.

The Lassen volcanic highlands are the source of water for springs where Shasta crayfish are found in the Hat Creek Basin. Precipitation on the Lassen volcanic highlands percolates through the lava into a large central aquifer system underlying Hat Creek Valley, which supplies water to Rising River and Crystal Lake springs.

Shasta crayfish are generally found in the cold, clear, spring-fed headwaters of the midsections of the Pit River drainage, particularly in the headwaters of the Fall River subdrainage. In general, Shasta crayfish habitat is defined by the availability of cover, or refugia (protected places), provided by clean lava cobbles and boulders on gravel or sand. Although potential food resources, temperature, and water chemistry, such as dissolved oxygen, calcium, and pH, may also limit the distribution of Shasta crayfish, the range of these conditions where Shasta crayfish are found is considerable.

The Bear Creek substrate is composed of silt, sand, Bear Creek gravel, lava gravel, lava cobbles, lava boulders, lava bedrock, diatomaceous earth/clay (earth composed of the shells of diatoms, a type of unicellular algae), or earthen clumps.

Shasta crayfish in the upper Tule River were found in two distinctly different habitat types that had only lava substrate in common. The spring areas were characterized by constant temperature, flow, and clarity, and the lava substrate in the immediate spring areas was clean, with relatively little silt. The headwater spring areas of the upper Tule River are much more turbulent.

Distribution

This species is endemic to a portion of the Pit River basin in extreme northern California. The Pit River arises in the mountains above the town of Alturus and flows south and west to empty into Shasta Lake. A population recorded from Sucker Spring Creek was extirpated before 1970. Populations documented from Lake Britton, Burney, Clark, Kosk, Goose, Lost, and Rock creeks disappeared some time before a 1974 census. Since 1978 the crayfish has disappeared from Baum Lake and Spring Creek.

The Shasta crayfish is currently found in the Pit River and in the watersheds of two of its tributaries—Hat Creek and Fall River (Modoc, Lassen, and Shasta counties), California. The largest concentrations of crayfish are found in the Fall River feeders—Big Lake and Tule River, Mallard, Squaw, and Lava creeks, and Crystal, Thousands, and Rainbow springs. Lesser densities occur in the Hat Creek feeders, Rising River Lake and Lost Creek. In 1980 the total population was estimated at less than 6,000 individuals, but had declined significantly by 1988.

As a result of construction of physical barriers and other disturbances that created large stretches of unsuitable habitat, Shasta crayfish became isolated into eight populations; however, only seven populations survive. The Fall River population, which was probably originally much more continuous than present, is now separated into four geographically isolated populations: (1) upper Fall River, (2) Spring Creek, (3) Lava Creek, and (4) upper Tule River, including Ja-She Creek, upper Tule River, and Big Lake. The (5) Fall River, Fall River Mills population is considered extirpated. The remaining populations include the (6) Pit River, (7) Hat Creek, Cassel, and (8) Rising River populations. The seven existing populations comprise several locations or subpopulations that may or may not have genetic exchange through interbreeding.

The largest population of Shasta crayfish, estimated at more than 4,000 individuals, is found in Spring Creek upstream of the four culverts at the Spring Creek Road crossing. Under normal flow conditions, the culverts at the Spring Creek Road crossing appear to create a barrier to the upstream invasion of signal crayfish.

Threats

Because the Shasta crayfish is slow to reach sexual maturity and has a low rate of reproduction, it is being displaced by two faster-breeding species of introduced crayfishes (Pacifastacus leniusculus and Orconectes virilis ). These crayfishes reach sexual maturity within two years, and each female lays up to 150 eggs. Since 1978 more than half of the Shasta's historic range has been taken over by these aggressive species.

Human activities have also played a role in the Shasta crayfish's decline. Streams and springs have been impounded and diverted into artificial channels to support irrigation agriculture. Agricultural chemicals have washed into streams, degrading water quality, and excessive pumping of groundwater has lowered the water table.

Development of the Fall River and Hat Creek Valleys for hydroelectric production began in 1920. Major land reclamation and water diversion projects for agriculture and cattle grazing began even earlier in the Fall River Valley. These activities further divided the population of Shasta crayfish into isolated pockets. The introduction of normative species of fish and crayfish into the drainage has also had a significant negative impact on Shasta crayfish. Many species of fish introduced into the area are known to prey on crayfish, and the introduced crayfish can be predators and competitors of the Shasta crayfish as well. In addition, natural disturbances resulting from the eruptions of Lassen Peak, floods, and drought have likely had a significant negative impact on Shasta crayfish.

Hydroelectric development, including the operation of four powerhouses in the midsections of the Pit River, represented one of the first broad-scale disturbances to the Shasta crayfish population. The range of Shasta crayfish and other aquatic species was divided into at least five regions by 1922 due to habitat alterations, such as excavations, river impoundments, water diversions, inundations, and changes and reductions of flows. Some of the habitat alterations decreased the amount of available lava substrate.

Some secondary effects resulting from hydro-electric operations and management in the area include increased siltation and water temperature and decreased dissolved oxygen content in impounded sections. In 1964, California Department of Fish and Game constructed the Pit River Fish Hatchery. Heavy machinery was used in the stream channel to remove boulders, and Shasta crayfish were most likely crushed. Almost all of the preferred substrate for Shasta crayfish, lava cobble and boulders, was removed. River gravel was placed in the channel to facilitate hatchery. A dam across the Sucker Springs Creek upstream has caused siltation and sedimentation, eliminating any remaining Shasta crayfish habitat upstream. The dam has also improved habitat for snails (Fluminicola spp.) that are the intermediate host for the gill fluke, a common parasite that causes hatchery fish mortality. Sucker Springs Creek was chemically treated on several occasions as either a treatment for, or prevention of, some trout diseases. In 1994, 2,400 lbs (1089.6 kg) of salt was added to the stream to exterminate snails. Salting is a nonspecific treatment that is harmful and even lethal to Shasta crayfish.

Six major activities associated with fisheries and fisheries management have affected Shasta crayfish: (1) the introduction of non-native crayfish species; (2) the introduction of non-native game fish species to provide sport fishing, with or without the sanction of California Department of Fish and Game and other agencies; (3) the introduction of potential cray-fish pathogens by introduced species; (4) the management of hatcheries and hatchery trout; (5) the restoration and improvement of wild trout habitat; and (6) crayfishing. These activities have contributed to the observed decrease in the distribution and abundance of Shasta crayfish.

Within the last two decades, two species of non-native crayfish have been introduced into the midsections of the Pit River drainage. The Virile crayfish was introduced in the 1960s, and the signal crayfish was introduced in the 1970s. The introduction of both species probably resulted from angling and the use of crayfish as bait. Virile crayfish have since been replaced throughout most of their range by signal cray-fish. The signal crayfish has rapidly expanded its range throughout most of the Pit River drainage and occurs with Shasta crayfish in at least a portion of five of the seven populations. The rapid expansion of signal crayfish has been linked to the diminished distribution of Shasta crayfish within their range.

Signal crayfish have all the characteristics of a classic invading species; they are larger, more aggressive, faster growing, earlier maturing, produce more offspring, and have a larger native range than Shasta crayfish. Signal crayfish also have a broader diet, greater physical tolerance to water temperature and quality, and a higher daytime activity rate than Shasta crayfish. In contrast, Shasta crayfish are slower growing, with a long generation time, a smaller native range, a more restricted diet, a narrower tolerance range of physical conditions, and a smaller body size at all ages than signal crayfish. Signal crayfish are aggressive and cannibalistic, and Shasta crayfish do not change their behavior to avoid signal crayfish, making Shasta crayfish vulnerable to competition and predation. Signal crayfish also carry several diseases, including those resulting from fungal (crayfish plague), protozoan, bacterial, and viral agents. Signal crayfish both carry and are resistant to the fungus that causes crayfish plague.

The introduction of exotic species of fish and crayfish, which are potential predators, competitors, and sources of new diseases and pathogens, is one of the biggest threats to the continued existence of the Shasta crayfish. Many species of game fish were intentionally introduced into the Pit River to provide sport fishing opportunities, including brown trout, largemouth bass, smallmouth bass, black crappie, green sunfish, black bullhead, brown bull-head, and channel catfish, all known to prey on crayfish. Common carp, which have also been introduced in the area, eat invertebrates living on river and lake bottoms.

Many native and introduced fish, amphibian, reptile, and mammal species in the midsections of the Pit River drainage are known to prey on cray-fish. Other potential predators include bullfrogs, turtles, garter snakes, mammals, and a variety of birds. Bullfrogs, which are not native west of the Rockies, were introduced and are now common in Crystal Lake and Big Lake. Bullfrogs and garter snakes prey on crayfish.

Two of the three native aquatic mammals, river otters and mink, are known to prey on crayfish. Observations of a pair of river otters feeding on signal crayfish in the Pit River indicate that they are extremely effective and efficient crayfish predators. Most of the river otter scat found in the area is composed solely of pieces of crayfish shell. Muskrats, which prey on crayfish, were introduced into the drainage in the early 1930s. Racoons are also known to eat crayfish.

Conservation and Recovery

Between 1990 and 1995, three projects were initiated to study and/or manage Shasta crayfish, which included ecology and competition studies, competitor control and habitat improvement, and disease and fungus control studies. Habitat enhancement has been initiated in the Upper Fall River during the course of surveys for Shasta crayfish. Lava rocks covered by sediment were turned over and laid on top of the sediment to provide refugia for Shasta crayfish.

The invasion of non-native crayfish species, in particular signal crayfish, is the single largest threat to the continued existence of Shasta crayfish. The continued existence of Shasta crayfish will be ensured when the subpopulations of the seven remaining populations are protected from the invasion of non-native species, particularly signal crayfish, and from other disturbances. Spring Creek and Rising River are the only two populations where all subpopulations are currently free of non-native crayfish; all of the Hat Creek and Pit River subpopulations have been invaded.

The primary recovery goal is to protect and stabilize the known Shasta crayfish subpopulations, which will maintain the genetic diversity of the species. An important task is the designing, testing, and installing of efficient barriers that will prevent signal crayfish invasions. Other site-specific tasks include habitat restoration and enhancement, working with landowners, improving land use practices, eradicating signal crayfish, stabilizing river and stream banks with plantings, developing dredging alternatives, eliminating fish hatchery operations, and establishing fishing restrictions.

Contact

Regional Office of Endangered Species
U.S. Fish and Wildlife Service
Eastside Federal Complex
911 N. E. 11th Ave.
Portland, Oregon 97232
http://pacific.fws.gov/

References

Daniels, R. A. 1980. "Distribution and Status of

Crayfishes in the Pit River Drainage, California." Crustaceana 38:131-138.

Eng, L. L., and R. A. Daniels. 1982. "Life History, Distribution, and Status of Pacifastacus fortis." California Fish and Game 68:197-212.

Schwartz, F. J., R. Rubelmann, and J. Allison. 1963."Ecological Population Expansion of the Introduced Crayfish Orconectes virilis." Ohio Journal of Science 63:266-273.

U.S. Fish and Wildlife Service. 1988. "Determination of the Shasta Crayfish to Be an Endangered Species." Federal Register 53(190):38460-38464.

U.S. Fish and Wildlife Service. 1998. "Recovery Plan for the Shasta Crayfish." U. S. Fish and Wildlife Service. Atlanta.