Chasmistes cujus

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 of suspected, on the basis of morphology, to be of hybrid origin. Chasmistes and Deltistes are closely related to the older, more diverse, widespread genus Catostomus; Chasmistes species are distinctive in having branched gill rakers and a terminal mouth (Scoppettone and Vinyard 1991).

Harris and Mayden (2001) used molecular data to examine phylogenetic relationships of major clades of Catostomidae. In all trees, Scartomyzon was paraphyletic and embedded in Moxostoma, and Catostomus was never recovered as monophyletic (Xyrauchen was embedded within Catostomus). They concluded that the phylogenetic relationships and taxonomic composition of taxa presently included in Moxostoma and Scartomyzon are in need of further study, as are the relationships and composition of the genera Catostomus, Chasmistes, Deltistes, and Xyrauchen, and the phylogenetic affinites of Erimyzon and Minytrema.

See Smith (1992) for a study of the phylogeny and biogeography of the Catostomidae.

Occurs only in Pyramid Lake and Truckee River, Nevada; major problem is reduced flow and water quality of the Truckee River, the only spawning area.

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.

This species is represented by only one occurrence.

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 ll 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).