|Scientific Name:||Xyrauchen texanus|
|Species Authority:||(Abbott, 1860)|
Catostomus texanus Abbott, 1860
|Red List Category & Criteria:||Critically Endangered A2bce ver 3.1|
|Reviewer/s:||Smith, K. & Darwall, W.R.T.|
|Facilitator/s:||Hammerson, G.A. & Ormes, M.|
This species is listed as Critically Endangered because the size of the wild population probably has declined by at least 80 percent over the past three generations (generation time is uncertain, but three generations probably spans at least a few decades). Decline is primarily due to the effects of dams and introduced fish species.
|Range Description:||This species' range historically included most of the Colorado River basin, from Wyoming and Colorado to Sonora and Baja California (Page and Burr 2011). Now it is much reduced in range and abundance. Currently the species is found in small numbers in the Green River (wild population being augmented), Yampa River (low numbers), White River (low number below Taylor Draw Dam), Duchesne River (small seasonal aggregations at mouth), upper Colorado River (low numbers), Gunnison River (wild population extirpated; being re-established through stocking), and San Juan River (wild population extirpated; being re-established through stocking); lower Colorado River between Lake Havasu and Davis Dam (spawned and produced larvae in early 2000s); reservoirs of lakes Mead and Mohave (population being augmented); in small tributaries of the Gila River sub-basin (Verde River, Salt River, and Fossil Creek; limited distribution of hatchery stocks; no self-sustaining populations); and in local areas under intensive management such as Cibola High Levee Pond, Achii Hanyo Native Fish Facility, and Parker Strip (USFWS 2002).
Major known spawning areas in Lake Mohave include Cottonwood Cove, Arizona Bay, Six-mile Cove, and Eldorado Canyon (Minckley et al. 1991). An ongoing stocking program is attempting to enhance the number of suckers that reach maturity in Lake Mohave where few young fish escape predation by non-native fishes.
Since the late 1980s, the Arizona Game and Fish Department has attempted to establish populations in the Verde and Salt rivers through stocking, but few fish survive.
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 four miles of the Yampa River, rarely occurring upstream as far as the Little Snake River. Spawning has been documented in lower Yampa River near confluence with Green River and in the upper Green River (Tyus and Karp 1989). Adults overwinter in the Echo Park area of Dinosaur National Monument (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 (D. L. Propst pers. comm. 26 October, 2000). The project started in 1995 and New Mexico Game and Fish documented reproduction in 1998 and 1999.
Razorback Suckers were recorded in the late 1980s 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).
See Minckley et al. (1991) for a detailed account of the historic and present distribution and abundance.
|Range Map:||Click here to open the map viewer and explore range.|
This species is represented by just a few extant spawning populations. Total adult population size appears to be not more than a few thousand (perhaps fewer than or not many more than 5,000).
The largest population is in Lake Mohave, where an ageing population of a few thousand adults (Marsh et al. 2003) is being enhanced by stocking of larger juveniles. The Green River subbasin population appears to only several hundred (fewer than 1,000) (USFWS 2002). Upper Colorado River subbasin population is very small, with no evidence of young since the 1960s (USFWS 2002). San Juan River contains only hatchery-reared stock that has survived and reproduced to some extent (USFWS 2002). It is estimated that there are more than 1,000 Razorback Sucker in the 60-mile reach of the lower Colorado River between Davis Dam and Lake Havasu, with evidence of reproduction (see USFWS 2002). Lake Mead contains an estimated 400 adults (late 1990s) (see USFWS 2002).
Area of occupancy, number of subpopulations, and population size have declined dramatically compared to the historical situation. See Marsh and Minckley (1989), Minckley et al. (1991), USFWS (1997, 2002), and Marsh et al. (2003) for information on historical status, decline, present status, and threats.
Population size is still declining. For example, the population in Lake Mohave (the largest remaining subpopulation) declined from 44,000 (also reported as 60,000) 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 1980s (Lanigan and Tyus 1989); more recent data suggested a decline to about 500; population has been characterized as stable or declining slowly, with some evidence of recruitment (USFWS 1997, 2002). In the upper Colorado River, the number of Razorback Suckers captured has decreased dramatically since 1974 (USFWS 2002).
|Habitat and Ecology:||
Habitats required by adults in rivers include deep runs, eddies, backwaters, and flooded off-channel environments in spring; runs and pools often in shallow water associated with submerged sandbars in summer; and low-velocity runs, pools, and eddies in winter. Spring migrations of adult Razorback Sucker were associated with spawning in historic accounts, and a variety of local and long-distance movements and habitat-use patterns have been documented. Spawning in rivers occurs over bars of cobble, gravel, and sand substrates during spring runoff at widely ranging flows and water temperatures (typically greater than 14°C). Spawning also occurs in reservoirs over rocky shoals and shorelines. Young require nursery environments with quiet, warm, shallow water such as tributary mouths, backwaters, or inundated floodplain habitats in rivers, and coves or shorelines in reservoirs. Source: USFWS (2002).
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 (Sigler and Miller 1963). It has been collected in flooded gravel pits along the Colorado River, Colorado, and from irrigation canals along lower Colorado River (juveniles, Marsh and Minckley 1989). In the nonbreeding season, adults were most common in shoreline runs and along mid-channel sand bars in the mainstream Green River, with average water depth of less than 2 m and 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 shallowly flooded stands of salt cedar and, in some cases, cobbled shorelines (Karp and Mueller 2002). Limited data indicate that 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 6 m (often in water less than 0.6 m 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). Mature 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, 21 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 (see USFWS 1990); apparently they prefer the shallow littoral zone for a few weeks after hatching, then disperse to deeper waters (see Federal Register, 21 March 1994, p. 13375). Seasonally inundated flood plains provide favourable feeding areas for young.
Threats to the species include streamflow regulation, habitat modification, competition with and predation by non-native fish species, and pesticides and pollutants (USFWS 2002).
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). Low recruitment results primarily from predation on larvae and juveniles by introduced fishes (Marsh et al. 2003). 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 a paucity of spawning adults. Hybridization with other suckers is a potential problem in some locations (Tyus and Karp 1990, Minckley et al. 1991).
See USFWS (1990) for many details on habitat changes that have affected this species.
Population maintenance 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.
|Citation:||NatureServe 2013. Xyrauchen texanus. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. <www.iucnredlist.org>. Downloaded on 09 December 2013.|
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