Chasmistes cujus 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Actinopterygii Cypriniformes Catostomidae

Scientific Name: Chasmistes cujus Cope, 1883
Common Name(s):
English Cui-ui
Taxonomic Notes: Buth et al. (1992) found that Chasmistes cujus and Catostomus tahoensis were diagnostically different for 20 genetic characters; they found no genetic evidence of hybridization in a sample suspected, on the basis of morphology, to be of hybrid origin.

Assessment Information [top]

Red List Category & Criteria: Endangered B1ac(ii,iv)+2ac(ii,iv) ver 3.1
Year Published: 2014
Date Assessed: 2011-11-02
Assessor(s): NatureServe
Reviewer(s): Smith, K. & Darwall, W.R.T.
Facilitator/Compiler(s): Hammerson, G.A. & Ormes, M.
This species is listed as Endangered because the extent of occurrence is less than 5,000 sq km, area of occupancy is less than 500 sq km, the species occurs in only one location, and the availability of spawning habitat (and thus the number of adults that spawn) is subject to extreme fluctuations related to multi-year changes in water availability.
Previously published Red List assessments:

Geographic Range [top]

Range Description:This species is endemic to Pyramid Lake (490 square kilometers), Nevada. Formerly it occurred in Winnemucca Lake (dried up in the 1930s). It migrates up the tributary Truckee River to spawn; historically it spawned as far as 40 km upstream in the Truckee River (USFWS 1992). Currently, adults use the lower 19 km (12 miles) of the Truckee River only during the spawning season and only in years in which there is sufficient attraction flow and passage above or around the delta (Scoppettone et al. 1986); most spawners use the 16-km (10-mile) reach between Marble Bluff and Numana dams; the fish ladder at Numana Dam is not conducive to passage of Cui-ui (USFWS 1992). Previously the species also occurred in Winnemucca Lake, which went dry in the 1930s due to water diversion.
Countries occurrence:
United States
Additional data:
Extreme fluctuations in area of occupancy (AOO):Yes
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:This species is represented by only one occurrence.

In the early 2000s, spawning runs were low or nil, following a run of 585,000 in 1999. Then high flows stimulated a run of several hundred thousand in 2005.

Adult population size evidently has increased over the past three generations (probably 50-75 years). Abundance of spawning Cui-ui is erratic but generally has increased since the early 1980s.

Spawning run of 13,000 in 1982 was the largest in recent years (up to that time). In 1983, 187,000 Cui-ui were estimated in the pre-spawning aggregation; however, about 92% were derived from the 1969 year class and most of the remainder were hatched in 1950; there was no significant recruitment between 1950 and 1969.

Cui-ui status improved when they spawned successfully from 1980 through 1987 in conjunction with unusually wet years. The adult population increased to over 500,000 by 1991 and exceeded 1 million by 1992 (Scoppettone and Rissler 1995). This increase probably resulted from maturation of the cohorts that hatched in the early 1980s (Scoppettone and Rissler 1995). However, subsequent lower water levels again resulted in insufficient water for spawning runs (Scoppettone and Rissler 1995).

In the early 2000s, spawning runs were low or nil, following a run of 585,000 in 1999. Then high flows stimulated a run of several hundred thousand in 2005.
Current Population Trend:Increasing
Additional data:
Extreme fluctuations:YesPopulation severely fragmented:No

Habitat and Ecology [top]

Habitat and Ecology:Habitat includes inshore lake areas with extensive shoals and shallow bars. Generally this species avoids deep-water areas and inshore areas with steep dropoffs (though Page and Burr [2011] described the habitat as "deep water"). Usually it occurs at depths of less than 46 meters (Sigler and Sigler 1987).

Spawning occurs in the Truckee River over gravel beds in relatively shallow water (21-140 cm) where flow is rapid. When runs are disturbed by low water levels, spawning may occur at the river mouth. Spawning may occur in Pyramid Lake, but extreme alkalinity and elevated salinity preclude successful reproduction there (Scoppettone and Vinyard 1991). Newly emerged young remain in the spawning stream for a few days or weeks.
Movement patterns:Full Migrant

Use and Trade [top]

Use and Trade: This species was formerly subject to intensive fishing.

Threats [top]

Major Threat(s): Endangered status is due to habitat alteration (siltation, pollution) and declining flow in the Truckee River (dam construction and water diversion). For many years access to the spawning habitat was difficult or impossible due to low water level in the lake and low flow in the river.

Current threats include loss of adequate water flow in the Truckee River, declining water quality resulting from the expanding urban population, and increased salinity in the lake that could result from mass water diversions (Scoppettone and Vinyard 1991). Inflow to Pyramid Lake is often insufficient to attract spawners or to stimulate fish movement into the river or Pyramid Lake Fishway (USFWS 1992). Sediment loads in the river, in conjunction with declining lake elevation, have created an extensive delta across the mouth that is frequently a barrier to upstream passage of Cui-ui spawners (USFWS 1992).

Pollutants from point and nonpoint sources enter the entire Truckee River from municipal, agricultural, and industrial sources; this results in high levels of nutrient loading to the river and Pyramid Lake (USFWS 1992). Increased temperatures and sediment loading, decreased dissolved oxygen and wetted perimeter, and other parameters have all reduced habitat quality for Cui-ui (USFWS 1992).

Ownership of water rights in the Truckee basin has been in dispute and subject to litigation for many years (Scoppettone and Vinyard 1991).

Conservation Actions [top]

Conservation Actions: Actions needed include the following (USFWS 1992):
  1. Secure Cui-ui spawning and rearing habitat by increasing inflow to Pyramid Lake, rehabilitating floodplain, achieving water quality standards, and improving fish passage.
  2. Conduct research to collect new information to refine Cui-ui model.
  3. Use Cui-ui model to evaluate benefits of conservation measures.
  4. Manage Cui-ui spawning runs.
  5. Protect Cui-ui population from extinction.

Citation: NatureServe. 2014. Chasmistes cujus. The IUCN Red List of Threatened Species 2014: e.T4586A3003395. . Downloaded on 17 August 2018.
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