|Scientific Name:||Catostomus warnerensis Snyder, 1908|
|Red List Category & Criteria:||Endangered B1ac(ii)+2ac(ii) ver 3.1|
|Reviewer(s):||Smith, K. & Darwall, W.R.T.|
|Facilitator/Compiler(s):||Hammerson, G.A. & Ormes, M.|
This species is listed as Endangered in view of the small extent of occurrence (less than 5,000 sq km), small area of occupancy (typically less than 500 sq km), small number of locations (here regarded as not more than five), and extreme fluctuations in area of occupancy (and likely also population size) resulting from multi-year changes in the amount of available habitat.
|Previously published Red List assessments:|
|Range Description:||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]
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||This species is represented by essentially one metapopulation, the subpopulations of which fluctuate with water availability.|
Total adult population size is unknown but appears to be at least several thousand. USFWS (1998, 2010) provided summaries of available data.
Extent of occurrence, area of occupancy, number of subpopulations, and population size vary with water availability. In general, population size appears to have declined greatly compared to the historical situation (see USFWS 1998). The degree of decline is unknown.
In general, trends are characterized by large fluctuations.
|Current Population Trend:||Unknown|
|Habitat and Ecology:||Habitat includes lakes, ephemeral bodies of water, streams, beaver ponds, and pools and runs of streams and large irrigation canals (Lee et al. 1980, Page and Burr 2011). Adults in streams tend to be in pools. In lakes, suckers are generally found in the deepest available water (generally less than 3.4 meters deep) where food is plentiful (USFWS 1998).|
Spawning occurs over silt-free sand or gravel substrates in slow pools in low gradient streams (White et al. 1990, Kennedy and North 1993). At least some young move immediately into lakes (Lee et al. 1980). In years when access to stream spawning areas is limited by low flow or by physical in-stream blockages (such as beaver dams or diversion structures), suckers may attempt to spawn on gravel beds along the lake shorelines (White et al. 1990).
Larvae occupy shallow backwater pools or on stream margins where there is no current, often among or near macrophytes. Young-of-the-year are often found over deep, still water from midwater to the surface, but also move into faster flowing areas near the heads of pools (Coombs et al. 1979). Juvenile suckers (1-2 years old) are usually found at the bottom of deep pools or in other habitats that are relatively cool and permanent such as near springs. As with adults, juveniles prefer areas of the streams which are protected from the main flow (Coombs et al. 1979).
|Movement patterns:||Full Migrant|
|Use and Trade:||This species is not utilized.|
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).
"Recovery of the Warner Sucker will depend upon the construction of fish passage structures to interconnect population segments and allow access to spawning habitat in streams, screening of diversions to avoid direct take of individuals, and stream flow management strategies to ensure adequate flows to sustain all life stages and histories of Warner Sucker. Additionally, control of non-native fish will help to maintain the lake morph life history of the Warner Sucker. The development and implementation of these necessary measures is expected to have a high level of conflict because: 1) the utility and additional costs and maintenance of fish passage and screening projects are a concern to some private landowners; 2) water in the Warner basin is already the subject of conflict by water users in the basin; and 3) the non-native fish in the Warner Lakes are a popular recreational fishery." Source: USFWS (2010).
See "Recovery plan for the native fishes of the Warner basin and Alkali subbasin" (USFWS 1998).
|Citation:||NatureServe. 2014. Catostomus warnerensis. The IUCN Red List of Threatened Species 2014: e.T4051A2932919.Downloaded on 19 February 2018.|
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