|Scientific Name:||Xyrauchen texanus|
|Species Authority:||(Abbott, 1860)|
Catostomus texanus Abbott, 1860
|Red List Category & Criteria:||Critically Endangered A2ae ver 3.1|
|Assessor/s:||NatureServe (G. Hammerson)|
|Reviewer/s:||Dowling, T.E., Marsh, P.C., & Schooley, J.D. (Freshwater Fish Red List Authority), Collen, B., Richman, N. and Ram, M. (Sampled Red List Index Coordinating Team)|
Xyrauchen texanus has been assessed as Critically Endangered under criterion A2ae. A population decline of almost 99% has been observed over the past 30 years due to a number of factors. Since its original assessment in 1996, repatriation efforts have been met with little success due to a number of intrinsic factors. Effort should now be directed towards creating habitat space free of predators, and management of key nursery habitats before this species becomes extinct.
|Range Description:||Xyrauchen texanus formerly occurred throughout the Colorado River basin, from Wyoming and Colorado to Sonora and Baja California. This species is now much reduced in range and abundance. The largest extant population occurs in Lake Mohave (lower Colorado River); small numbers occur in Lake Mead, Lake Havasu, and the Grand Canyon (transitory in Grand Canyon; Douglas and Marsh 1998). Major known spawning areas in Lake Mohave include Cottonwood Cove, Arizona Bay, Six-mile Cove, and Eldorado Canyon. An ongoing stocking program is attempting to enhance the number of suckers that reach maturity in Lake Mohave where young fish escape predation by non-native fishes. Since the early 1980's, the USFWS and Arizona Game and Fish Department have attempted to establish populations in the Gila, Verde and Salt rivers through stocking, but no fish survive in the long-term. In the upper Colorado River Basin, adults and larvae are widely distributed in the Green River basin, especially in the upper basin from the mouth of the Duchesne River, upstream to the lower 4miles of the Yampa River, rarely occurring upstream as far as the Little Snake River. Spawning has been documented in lower Yampa River near the confluence with Green River and in the upper Green River (Tyus and Karp 1989). A small reproducing population exists in the lower Green River. In the upper Colorado River, most suckers occur in the Grand Valley (mainstem Colorado River and Gunnison River, Colorado). A reproducing population occurs in an off-channel pond in the Colorado River near Grand Junction. A few have been found in the San Juan River above Lake Powell, and adults have been found in the San Juan and Colorado River arms of the lake (USFWS 1997). The species is currently considered extant in New Mexico, based on ongoing reintroduction efforts in the San Juan River Basin (J. Fowler-Propst 2007 pers. comm.). The project started in 1995 and New Mexico Game and Fish documented reproduction in 1998 and 1999. Adults overwinter in the Echo Park area of Dinosaur National Monument (Tyus and Karp 1989). Razorback suckers were recorded in the late 1980's along the south shore of Lake Powell near the concrete boat ramp at Piute Farms Marina and near Bluff, Utah. The Lake Powell record apparently represented a spawning aggregation or staging prior to spawning elsewhere (Platania et al. 1991). The area in which this species is distributed, is approximately 126,593 km².|
|Range Map:||Click here to open the map viewer and explore range.|
Xyrauchen texanus is represented by just a few extant spawning populations, none of which exhibit sustained recruitment (Dowling et al. 1996).
Total wild adult population size appears to be not more than a few thousand. The largest population is in Lake Mohave, where an ageing population of a few hundred wild adults (Marsh et al. 2003) is being enhanced by stocking of larger juveniles. Before a recent decline, Lake Mohave was believed to contain about 90 percent of the total population. Adult population size outside Lake Mohave may be less than 1,000.
Area of occupancy, number of subpopulations, and population size have declined dramatically compared to the historical situation. Population size is still declining. For example, the population in Lake Mohave (the largest remaining subpopulation) declined from 44,000 in 1991 to fewer than 3,000 in 2001 (Marsh et al. 2003). The population in the upper Green River basin was estimated at about 1,000 adults in the late 1980's (Lanigan and Tyus 1989); more recent data suggests a decline to about 500 adult individuals (USFWS 1997).
|Habitat and Ecology:||
Xyrauchen texanus habitat types include slow flowing areas, backwaters, and eddies of medium to large rivers and their impoundments (three of the four remaining populations of greater than 100 individuals are in reservoirs). Flooded lowlands and lower portions of tributary streams presumably served as resting-feeding areas during breeding season in the Green River basin (Tyus and Karp 1990). This fish is often associated with sand, mud, and rock substrate in areas with sparse aquatic vegetation, where temperatures are moderate to warm. It has been collected in flooded gravel pits along the Colorado River, and from irrigation canals along the lower Colorado River (juveniles, Marsh and Minckley 1989). In the non-breeding season, adults were most common in shoreline runs and along mid-channel sand bars in the mainstream Green River, with an average water depth of less than 2 m, and an average velocity of less than 0.5 m per second (Tyus and Karp 1989). Radio-tagged suckers reintroduced into the Gila River, Arizona, used both sand-bottomed, flat-water, main-channel habitats and quieter pools and eddies adjacent to stronger currents (see Minckley et al. 1991). Hatchery-reared suckers released into the San Juan River inflow of Lake Powell most often used shallow, flooded stands of salt cedar and, in some cases, cobbled shorelines (Karp and Mueller 2002). Limited data indicate that the young tend to remain along shorelines, in embayments, along sandbars, or in tributary mouths (see Minckley et al. 1991). In Lake Mohave, individuals were associated with inshore habitats except during the hotter months when they moved offshore possibly to avoid warmer water temperatures (Mueller et al. 2000).
Spawning occurs most commonly near shore in streams over silty sand, gravel, or rock substrate at depths of up to about 6m (often in water less than 0.6m deep); known and suspected spawning sites in the Green and other upper-basin rivers all are in broad, flat-water segments (Minckley et al. 1991). Ripe individuals often have been taken over or near coarse sand, or gravel or cobble bars, in flowing water. In reservoirs, spawning occurs on gravel bars swept clean by wave action; also along shorelines over mixed substrates ranging from silt to cobble (Federal Register 2i March 1994). Spawning has been observed downstream from major impoundments, below Davis Dam and Hoover Dam (Mueller 1989). Larvae appear to remain in gravel until swim-up (USFWS 1990); apparently they prefer the shallow littoral zone for a few weeks after hatching, then disperse to deeper waters (Federal Register 21 March 1994, p. 13375). Seasonally inundated flood plains provide favourable feeding areas for the young.
Xyrauchen texanus is threatened by interactions with non-native fishes and by human alteration of riverine habitat.
Recruitment is very low (or absent) despite spawning and hatched larvae (e.g. in upper Green River basin). For example, no recruitment to reservoir populations was detected between 1963 and 1990 in the lower Colorado River basin, despite collecting with appropriate equipment (Minckley et al. 1991). Poor recruitment is likely attributed to predation on this species by flathead catfish and avian piscivores (J.D. Schooley 2007 pers. comm.). Competition with and predation by exotic crayfish may also be a problem in some areas (Lenon et al. 2002).
Habitat changes resulting primarily from dam operations has greatly restricted the amount of suitable habitat; these detrimental changes include high winter flows, reduced high spring flows, altered river temperatures (Clarkson and Childs 2000), and reduced flooding (USFWS 1990).
Natural recovery is limited by pervasiveness of predatory non-native fishes which also contribute to political impediments to recovery (Clarkson et al. 2005). Hybridization with other suckers is a potential problem in some locations (Tyus and Karp 1990, Minckley et al. 1991).
See USFWS (1990) for details on habitat changes that have affected this species.
|Conservation Actions:||Population maintenance of Xyrauchen texanus depends on ongoing stocking of juveniles that are large enough to avoid predation by non-native fishes. Natural recruitment might be enhanced by appropriate management of floodplains that serve as important nursery areas along with the development of non-native free habitats (P.C. Marsh pers. comm. 2007). Management of the predation of this species by non-native species, will be the key success of this program (T.E. Dowling pers. comm. 2007).|
|Citation:||NatureServe (G. Hammerson) 2010. Xyrauchen texanus. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. <www.iucnredlist.org>. Downloaded on 23 May 2013.|
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