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CATOSTOMIDAE - Suckers
Xyrauchen is one of three monotypic genera in the family Catostomidae. The razorback sucker was originally described as Catostomus texanus from a specimen collected from Arizona (Abbott 1861). Eigenmann and Kirsch (Kirsch 1889) later described the genus Xyrauchen (Bestgen 1990). The morphology of the razorback sucker is distinguishable from all other catostomids by the dorsal keel rising posterior from the head. Primary dorsal fin rays are usually 14-15 (12-17), primary anal fin rays are usually 7, total vertebrae 45-47, scales in lateral series 68-87, and gill rakers 44-50 in the first arch (Bestgen 1990). Razorback sucker are robust in size and slightly compressed laterally. The upper body is dark brown to olivaceous and white or yellow on the lower ventro-lateral surfaces. During the spawning season males often have a lighter coloration and have well developed tubercles on the anal and caudal fins.
Razorback sucker have reached lengths of up to 1000 mm and weighed as much as 4.5 kg in the Lower Colorado River Basin (Bestgen 1990, Minckley et al. 1991). Fish in the Upper Colorado River Basin tend to be somewhat smaller than those in the Lower Basin (the artificial boundary between the Upper and Lower Basins of the Colorado River is Lee's Ferry, Arizona). Mature females are, on average, larger than males in both the Upper and Lower Colorado River Basin populations. Growth rates vary considerably between the Upper and Lower Colorado River basins, with age 0 fish reaching lengths of up to 400 mm in the latter (Mueller et al. 1993) , whereas, average first year growth of wild fish in the Middle Green River was closer to 100 mm (T. Modde, U.S. Fish and Wildlife Service, unpublished data). In riverine habitats, razorback sucker mature after three to six growing seasons (McAda and Wydoski 1980). Razorback sucker are long-lived fish, reaching ages in excess of 40 years (McCarthy and Minckley 1987).
Listed on the Federal Register (USA) as an endangered species in 1991 (USFWS 1991).
The razorback sucker is endemic to the Colorado River drainage. Historically these fish occupied the major tributaries of the Colorado River Basin between southwestern Wyoming and northern Mexico (Minckley et al. 1991). In the Lower Basin, razorback sucker are found primarily in large Colorado River impoundments including Lake Mohave, Lake Meade and Lake Havasu. The largest population is found in Lake Mohave. Razorback sucker have been reintroduced into the Gila, Verde, and Salt Rivers of the Lower Colorado River Basin between 1981 and 1984, but, little evidence suggests that fish have successfully reestablished in these tributaries (Minckley et al. 1991). In the Upper Colorado River Basin razorback sucker are found regularly in the Green River, primarily between the confluence of the Duchesne and Yampa rivers (Tyus 1987). Razorback sucker have also been collected in the Lower Green River and in the Upper Colorado River (Grand Valley) (McAda et al. 1994). Small numbers of razorback sucker have also been collected in Colorado and San Juan arms of Lake Powell (Modde et al. 1995).
The greatest number of razorback sucker exist in Lake Mohave, Arizona (Minckley et al. 1991). Smaller numbers of fish are also found in other Lower Basin Colorado River impoundments (Bestgen 1990). These populations consist of old fish believed spawned during the filling of the reservoirs. Because little or no recruitment of these populations occurs, numbers are declining. Populations of razorback sucker have been observed to increase during the filling of several Lower Colorado River Basin reservoirs (Minckley 1983)) and subsequently disappeared after fish from these early cohorts died of senility. The population of razorback sucker in Lake Mohave was estimated to be approximately 73,000 between 1980 and 1993, 60,000 between 1988 and 1993, and 20,000 between 1991 and 1993 (Marsh 1993). The largest population of razorback sucker occupying native riverine habitat is in the Middle Green River (Lanigan and Tyus 1989). The population was estimated to be approximately 500 individuals between 1980 and 1992 (Modde et al. in press). Recruitment has been reported in the Middle Green River (Modde et al. in press), but, the population is believed to consist primarily of older individuals. Few individuals have been collected in the Lower Green River or the Upper Colorado River (Grand Valley) and no population estimates are available for these areas.
The few juvenile razorback sucker collected in riverine habitats have been found in low velocity main channel backwaters or off channel wetlands (Taba et al. 1965, Gutermuth et al. 1995, T. Modde, unpublished data). Adult razorback sucker habitat use is flexible, with fish surviving well in both lentic and lotic habitats (Modde et al. 1995). Following spawning in the Middle Green River, adults tend to move downstream to the mouths of tributaries and have commonly been collected in wetlands over 100 kilometers downstream of spawning sites (Tyus and Karp 1990, Modde and Wick 1995). Following declines in spring runoff, fish were observed to return upstream to within 50 kilometers of the primary spawning site. During baseflow periods, razorback sucker use main channel habitats including runs and eddies over a variety of substrates (Tyus 1987, Modde and Wick 1996). All life stages of razorback suckers apparently feed on plant debris, cladocerans, and aquatic insect larvae (Marsh and Langhorst 1988; Wick et al. 1982). Larvae feed mostly on phytoplankton and small zooplankton, cladocerans, copepods, and rotifers (Marsh and Langhorst 1988, Papoulias and Minckley 1992). Plankton such as cladocerans were important for young fish while aquatic insects (Ephemeroptera and Trichoptera) were important for adults in the Green River (Vanicek 1967). Diets of lacustrine populations of adult razorback suckers are composed primarily of planktonic crustaceans such as Cladocera (Minckley 1973; Marsh 1987). Detritus and plant debris may be ingested incidentally when the fish eat zooplankton and aquatic insects. The razorback sucker possesses fine gill rakers that suggests it may strain water for small invertebrates as food (Hubbs and Miller 1953).
Razorback sucker successfully reproduce in both lentic and lotic habitats (Minckley et al. 1991). Fish mature between the ages of 4 and 7 when they reach between 400 and 450 mm. In Lake Mohave fish spawn on wind swept cobble and gravel shorelines. Fish also spawn in the riverine habitat of the Hoover Dam tailwaters. Larvae successfully hatch, but, survival in Lower Colorado River Basin reservoirs appears negligible due to larval predation from nonnative fishes and possibly low prey densities (Minckley et al. 1991). Spawning occurs between November and May in the Lake Mohave (Bozek et al. 1990). In the Middle Green River, the razorback sucker spawns on the ascending limb of the hydrograph when water temperatures are between 7 and 18°C with an average of about 15°C between mid-April to mid-May (Tyus and Karp 1990). Razorback suckers spawn over gravel bars that are 0.1 to 1.0 meter deep with a water velocity between 0.1 and 0.6 meters per second (Wick et al. 1982). The duration of spawning varies with flow patterns, but generally lasts between four and six weeks (Tyus and Karp 1990, Modde and Wick, 1995). Although natural spawning occurs annually and larvae have been collected from the main spawning site on the Green River several miles upstream from Jensen, Utah to Lake Powell, few juvenile fish have ever been collected in the wild since the first studies during mid-1960's (Minckley et al. 1991). In 1995, twenty-eight age 0 razorback sucker were collected in a wetland on the Ouray National Wildlife Refuge following draining in October (T. Modde, unpublished data). The occurrence of fish in wetlands corroborates the contention of Tyus and Karp (1990), Modde et al. (1995) and Modde et al. (in press), that offchannel wetland habitats are important to the early life history of razorback sucker.
The greatest threats to the razorback sucker include alteration of natural flows regimes and interactions with nonnative predators (Minckley 1991). Both of these factors are interactive. Mainstem reservoirs in the Colorado River drainage have created barriers to spawning migrations, and nearly eliminated the natural hydrograph, removing riverine cues associated with migrations. Impoundment of the mainstem and major tributaries have transformed warm, turbid rivers with variable flows into clear, cold/cool water environments that, in some areas, are more suitable for nonnative salmonids than the cyprinid and catostomid fishes native to the system. Because reservoir environments and the riverine reaches controlled by reservoir releases are not characterized by the variation in flows, sedimentation, temperature, etc. characteristic of the historic environment, nonnative warmwater fishes have become more effective competitors and predators on native species, including the razorback sucker (Minckley et al. 1991). In addition, localized contaminant threats exist in the Upper Basin (Stephens et al. 1992). Selenium concentrations capable of impairing reproductive success has been reported in some razorback sucker in the Middle Green River (Waddell and May, 1995).
In 1988 an interagency effort formed the Recovery Implementation Program for the Recovery of Endangered Fishes in the Upper Colorado River to fund and administer recovery efforts for the razorback sucker (and also the Colorado squawfish, humpback chub and bonytail) above Lee's Ferry. This program is a consortium among the U.S. Fish and Wildlife Service, U.S. Bureau of Reclamation, Western Area Power Administration, the States of Utah, Colorado and Wyoming, the water user community and environmental interests. The program outlines a 15 year effort consisting of five elements: 1. Provision of in-stream flows 2. Habitat development and maintenance 3. Native fish stocking (including genetic management 4. Management of nonnative species and sport fishing 5. Research, monitoring and data management The program was initiated as a an alternative to Section 7 (of the Endangered Species Act) consultation for every individual water project in the Upper Basin by the U.S. Fish and Wildlife Service. An in-depth description of the program and its origins is provided by Wydoski and Hamill (1991). In the Lower Colorado River Basin cooperative, interagency efforts have also been organized to recover the razorback sucker. These efforts have been described in Minckley et al. (1991) and have included broad scale stocking efforts throughout the Lower Basin as well as intensive efforts to maintain the last large population of razorback sucker in Lake Mohave. The latter effort involves collecting wild spawned razorback sucker larvae in Lake Mohave annually and rearing them in fish predator free embayments with the reservoir. After the first growing season, fish are stocked back into Lake Mohave.
Compiled by Tim Modde and Dick Wydoski U.S. Fish and Wildlife Service Colorado River Fish Project 266 W. 100 N., Suite 2 Vernal, UT 84078 r6ffa_ver_at_mail.fws.gov December 10, 1995.
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(Dean Hendrickson) |
General information: (E. Phil Pister) |
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This page last modified: 06 June 2004