Catostomus warnerensis

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

Restricted to one small hydrologic basin in Oregon and very small areas in Nevada and California; threatened by habitat alteration (caused mainly by dams and diversions) and by predation by exotic fishes; these factors are exacerbated by drought.

This fish is endemic to the Warner Lake Basin in south-central Oregon, extreme northeastern California, and extreme northwestern Nevada (USFWS 2010). This range includes three permanent lakes, Hart, Crump, and Pelican; the ephemeral Anderson, Swamp, Mugwump, Flagstaff, Upper Campbell, Campbell, Stone Coral, and Bluejoint lakes; and all the sloughs and canals connecting these lakes; and three major stream basins that are tributaries to these lakes (Deep Creek, Twentymile Creek, and Honey Creek) (USFWS 2010).

Current distribution: When adequate water is present, Warner suckers may inhabit all the lakes, sloughs, and potholes in the Warner Valley (USFWS 1998). The documented range extended as far north into the ephemeral lakes as Flagstaff Lake during high water in the early 1980s and again in the 1990s (Allen et al. 1996). Stream resident populations are found in Honey Creek, Snyder Creek (tributary to Honey Creek), Twentymile Creek, and Twelvemile Creek. Intermittent streams in these drainages may support small numbers of migratory suckers in high water years (USFWS 1998). In the lower Twentymile Slough area on the east side of the Warner Valley, White et al. (1990) collected adult and young suckers throughout the slough and Greaser Reservoir. This area dried up in 1991. However, because of its marshy character, this area may be important sucker habitat during high flows. Larval, young-of-the-year, juvenile and adult suckers captured immediately below Greaser Dam suggest either a slough resident population or lake resident suckers migrating up the Twentymile Slough channel from Crump Lake to spawn (White et al. 1990, Allen et al. 1996). [Source: USFWS 1998]

This species is represented by essentially one metapopulation, the subpopulations of which fluctuate with water availability.

The major threats to the continued existence of the Warner sucker and other native fishes in the Warner Basin and Alkali Subbasin are human-induced stream channel and watershed degradation, irrigation diversion practices, and predation and competition from introduced fishes (USFWS 1998, 2010).

Irrigation dams and canals block access to some spawning streams, which may be negatively affected by water pollution and siltation. Natural decreases in water levels periodically reduce the sucker population during periods of drought, which are aggravated by irrigation demands for water. The introduction of exotic predaceous fishes to the Warner Valley in the early 1970s evidently led to large reductions in the numbers of Warner suckers, which previously had more extensive availability of safe rearing habitat, even with degraded stream conditions and blockages of migration corridors (USFWS 1998). Exotic fishes may also threaten the sucker through competitive interactions (USFWS 1998). Drying of the lakes in the early 1990s reduced but did not eliminate populations of exotic fishes (they persist in sloughs and ditches) (USFWS 1998).

This species remains vulnerable to predation by exotic fishes and is negatively affected by modification of habitat through the continued operation of water diversions and barriers that restrict movement and migration. Prolonged drought, particularly desiccation of lakes from drought and irrigation use and the drying or reduced stream flow of stream channels from irrigation water removal, greatly impact the species' viability and recovery (USFWS 2010).

The Warner sucker exists as two morphs, lake morph and stream morph. These face somewhat different threats. The lake morph suckers normally spawn in the streams, but they are often blocked from doing so by irrigation diversion structures or during low water years. Large lake-dwelling populations of introduced fishes have probably reduced recruitment by preying on young suckers. Stream habitat degradation has reduced suitable habitat and probably reduced the ability of stream morph suckers to withstand floods and droughts (USFWS 1998).