Xyrauchen texanus is endangered on the IUCN red list, endangered on the U.S. federal list, and does not have a designation by CITES. The razorback sucker was placed on the U.S. federal list as endangered on October 23, 1991. On March 21, 1994 a ruling set forth critical habitat for the species. The causes for this species' decline stem from massive habitat destruction and introduction of exotic invasive predator species. Alterations to the Colorado River, such as diverting water through canals and building dams, have altered the water flow, degraded the water quality, fragmented the habitat, and completely eliminated many of the ecosystems associated with the river system. With decreased turbidity in the water, predation rates on razorbacks increased because utilizing suspended sediments in the flow is part of the predator avoidance strategy of X. texanus. With the addition of countless non-native predatory fishes, the predation rate on larval and juvenile razorback suckers increased exponentially. Selenium contamination in the upper and lower basins of the Colorado River is also a problem facing razorback suckers. Selenium is accumulating in their tissues and eggs and is directly leading to increased mortality of larvae (Hamilton, Holley, and Buhl, 2002). The selenium contamination is also causing deformities(McDonald, et al., 2002). Non-point source pollution is leading to copper contamination in the Colorado River, which may affect razorback suckers, too(Hamilton, Buhl, 1997).
The Recovery Team is doing a variety of things to help recover this species. It has designated critical habitat to maintain the remaining integrity of the habitat. Captive rearing is another large part of the recovery program. Allowing the fish to grow in captivity past the age where they are vulnerable to most of the non-indigenous fish, allows for a much higher recruitment. There is a fine line between holding onto them too long and not long enough, however.
US Federal List: endangered
CITES: no special status
IUCN Red List of Threatened Species: critically endangered
Many species of fish feed on razorback larva. Other predators are birds, mammals, and some insects. Adults have few natural predators. Native Americans and early settlers, however, ate razorback suckers.
Most of the fish that presently predate on X. texanus are non-natives. Green sunfish and channel catfish (among many others) heavily predate razorback larvae. Since X. texanus did not evolve in an environment with a large concentration of predatory species, it is at a disadvantage. When compared to the northern hog sucker Hypentelium nigricans, a species adapted to a predator-rich environment, in laboratory experiments, X. texanus larvae had a significantly lower initial predator avoidance rate (Johnson, Pardew, and Lyttle, 1993). Habitat alteration has further amplified predation rates on X. texanus. Mainstream dams have severely reduced the turbidity of western river systems. The decrease in turbidity has a consequence of diminishing the amount of suspended sediments in the water. Razorback suckers use this suspended sediment for predator avoidance. Johnson and Hines (1999) found that as turbidity increases, X. texanus predation rates drop (Johnson and Hines, 1999).
Dragonfly and damselfly nymphs may be responsible for impacting larval razorback sucker survival. The abundance of backwaters that do not fully drain, combined with the exotic invasive sago pondweed has perhaps allowed large populations of odonates to form. In lab tests odonata nymphs appeared to pose a serious threat to X. texanus larvae (Horn, et al., 1994).
Downstream night movement is a possible predator avoidance mechanism for young razorback larvae (Tyus, et al., 2000).
Known Predators:
Xyrauchen texanus is a relatively large catostomid, reaching lengths of over 3 feet (91 cm) and weights of 5-6 kg (Gilbert and Williams, 2002; U.S. Fish and Wildlife Service). The sexes are dimorphic, and females are usually longer and more robust. The largest individuals are found in the warmer waters of the lower Colorado River. A study in the upper basin of the Colorado River found that females averaged 547 mm and males averaged 507 mm (U.S. Fish and Wildlife Service, 1998).
Razorback suckers look similar to average catastomids, except for two major features. The most defining characters of X. texanus are a pronounced ridge made of neural and interneural bones that extends from the head to the dorsal fins, and elongated filaments on the gill rakers (U.S. Fish and Wildlife Service). Females have a lower keel. The well-developed filaments are an adaptation for zooplankton feeding.
Xyrauchen texanus has a long snout, a long and rounded head that is ventrally compressed, and a ventral mouth with a cleft lower lip (Gilbert and Williams, 2002). The dorsal fin has 12 to 15 rays, and the anal fin has 7 rays. Pelvic and anal fins are longer in males. Xyrauchen texanus has a nearly straight lateral line with 68 to 87 scales (Gilbert and Williams, 2002).
The sexes are dimorphic, especially during the breeding season. In general the species is dark brown to olive on the dorsum, slightly lighter on the sides, and yellowish to white on the ventor. Males are much darker dorsally in the breeding season, and the sides and ventral area are orangish-yellow to bright orange. Tubercles appear on the anal and caudal fins, and on the ventral area of the caudal peduncle through the breeding season. These tubercles are more distinguished in the males.
Range length: 370 to 910 mm.
Average length: males 507; females 547 mm.
Sexual Dimorphism: female larger; sexes colored or patterned differently; male more colorful; ornamentation
Other Physical Features: bilateral symmetry
Razorback suckers are long-lived. The approximate maximum age is 50 years. Using otolith rings to age the fish, surveyers in Mojave Lake in the 1980's found adult fish between the ages of 24 and 44 years (U.S. Fish and Wildlife Service, 1998).
Range lifespan
Status: wild: 50 (high) years.
Xyrauchen texanus is adapted to a fluctuating river basin system with unpredictable and extreme flows and turbidity. In presettlement times, razorback suckers would have utilized backwaters, sloughs, inundated floodplains, and sand flats (U.S. Fish and Wildlife Service, 1998). Now the habitat is much different. Xyrauchen texanus must cope with human alterations, such as large dams, impoundments, channels and reservoirs. The habitat preference of adult razorbacks changes with seasons. Within rivers, razorbacks seem to prefer to spend most of their spring time in flooded areas. This likely aids in foraging and temperature regulation. They generally stay in water from 0.6 to 3.4 meters depth and 0.3 to 0.4 m/s water velocities (U.S. Fish and Wildlife Service, 1998). When summer comes, the fish occupy mid-channel sandbars in water less than 2 m deep and velocities around 0.5 m/s. Winter sees the razorback suckers utilizing eddies and slow runs with depths of 0.6 to 1.4 m and velocities from 0.03 to 0.33 m/s (U.S. Fish and Wildlife Service, 1998). Razorbacks have even been recorded moving in whitewater areas.
Within reservoir habitats, adult razorbacks move around throughout the different microsites, but prefer backwaters and main impoundments (Bradford and Gurtin, 2000). The larvae razorbacks move along the edge of bodies of water from the spawnig grounds to their nursery environments, large backwaters (Tyus, et al., 2000). They enter the drift at night and allow it to carry them to their new destination. Backwaters provide the larvae a more temperature regulated environment with more foraging opportunities. However, since the introductions of several exotic invasive fish predators, these seemingly safe havens are very dangerous places for the larvae. Within reserviors, shallow shorelines and coves may provide a similar nursery environment (U.S. Fish and Wildlife Service, 1998).
Xyrauchen texanus is sensitive to water temperatures, using it as a gauge for spawning times. Bulkley and Pimentel (1983) found the preferred temperature to be between 22.9 and 24.8 degrees Celsius. The upper avoidance boundary is between 27.4 and 31.6 degrees Celsius, and the lower boundary is between 8.0 and 14.7 degrees Celsius (Bulkley and Pimentel, 1983). Temperature can also play an important role in the development of early life stages of X. texanus (Clarkson and Childs, 2000).
Range depth: 0.5 to 18 m.
Habitat Regions: temperate ; freshwater
Aquatic Biomes: lakes and ponds; rivers and streams; temporary pools
Razorback suckers, Xyrauchen texanus (Abbott 1861) are restricted to a relatively small number of sites in the Colorado River system, from southwestern Wyoming to southeastern California. Xyrauchen texanus has a more stable population in the lower basin of the Colorado River than the upper basin. Within the lower basin, Lake Mojave, Arizona contains the greatest population of razorback suckers. They are also found in Lake Mead and the Grand Canyon, as well as in some associated canals and impoundments (Gilbert and Williams, 2002). In the upper basin of the Colorado River, the largest extant population is found in the Green and Yampa rivers.
Razorback suckers were once much more abundant and widely distributed. Xyrauchen texanus was found throughout the Colorado River and its major tributaries. As recent as the 1920's X. texanus was found in the Salton Sea (Gilbert and Williams, 2002). Human activities that have degraded and destroyed the physical and biological components of the habitat of X. texanus are directly responsible for the geographic range decline of this species.
Biogeographic Regions: nearctic (Native )
The diet of X. texanus depends on a variety of factors, including habitat, life stage, and availability of food.
In the wild larva and juvenile razorback suckers eat a wide variety of foods, when the mouth is terminal (U.S. Fish and Wildlife Service, 1998). As larvae, X. texanus eats primarily phytoplankton and zooplankton. In hatchery ponds larval and juvenile razorback suckers have been fed diets of brine shrimp and certain dry commercial products (U.S. Fish and Wildlife Service, 1998).
In Lake Mohave and other still waters, planktonic crustaceans, diatoms, filamentous algae, and detritus dominate the diet of razorbacks (Marsh, 1987). In riverine ecosystems, the species primarily feeds on immature Ephemeroptera, Trichoptera, and chironomids, as well as algae and detritus (U.S. Fish and Wildlife Service, 1998).
Animal Foods: carrion ; insects; aquatic crustaceans; zooplankton
Plant Foods: algae; phytoplankton
Other Foods: detritus
Primary Diet: carnivore (Insectivore ); detritivore
Razorback suckers are detritivorous and help perform the critical job of biodegredation. In addition to eating insects, crustaceans, and algae, razorbacks consume detritus and break it down so that it can be recycled back through the system. This species is also a food item for many other species.
The parasitic copepod, Lernaea cyprinacea, is known to use X. texanus as a host species. It is not been proven to have a serious effect on razorback recruitment (U.S. Fish and Wildlife Service, 1998).
Ecosystem Impact: biodegradation
Commensal/Parasitic Species:
Native Americans and early European settlers used razorback suckers for food and fertilizer (U.S. Fish and Wildlife Service, 1998). Since the 1950's this species' populations have been drastically reduced, and razorbacks are now federally endangered. Therefore, humans no longer use them for such purposes.
Positive Impacts: food ; produces fertilizer
There are no known adverse affects of X. texanus on humans.
More research is needed in this area in wild populations. Data show that when young life stages of X. texanus are exposed to water temperatures below 15 degrees Celsius, they experience significant reductions in growth rates (Clarkson and Childs, 2000).
Growth during the first six years of life is rapid for razorbacks. Newly-hatched larvae measure 7 to 9 mm and studies in the backwaters of Lake Mojave showed that some larvae grew up to an astounding 35 cm from January to November (U.S. Fish and Wildlife Service, 1998). Juveniles, similarly have been shown to grow over 40 cm in two months (U.S. Fish and Wildlife Service, 1998).
The growth of adult X. texanus is quite slow. They only seem to grow from 2.2 to 3.1 mm per year (U.S. Fish and Wildlife Service, 1998).
Very little is known about the communication techniques of this species. More research should be done to find out how they coordinate movement to spawning grounds and communicate between mates.
Data suggests that X. texanus use discharge as the primary cue for movement to spawning grounds (Modde and Irving, 1998). This would require a relatively sensitive tactile system in their lateral line organs to detect slight differences in discharge. Water temperature may also be an environmental cue timing spawning movements.
Larval razorbacks coordinate their downstream movements with darkness and increased water flow. They move very little during daytime and remain relatively sedentary during the night, unless stream flow is increased. Stream flow being increased during daylight hours does not seem to have the same effect (Tyus, et al., 2000), so Xyrauchen texanus may be sensitive to changes in ultraviolet radiation.
Communication Channels: tactile ; chemical
Perception Channels: visual ; infrared/heat ; ultraviolet; tactile ; chemical
Razorback suckers are polyandrous. Males aggregate together and when a female comes by, several males will pursue and position themselves for mating (U.S. Fish and Wildlife Service, 1998). The group spawns over a depression and then disperses.
Mating System: polyandrous
Spawning in razorback suckers seems to be tied to the increase of discharge and water temperature, and usually takes place from January through June, depending on the location (Mode and Irving, 1998; U.S. Fish and Wildlife Service, 1998). Spawning may take place in a variety of environments, including mainstreams, riverine-influenced impoundments, and wave-washed shorelines of impoundments, primarily over coarse sand substrate. The temperature linked to the best hatching percentage of razorback eggs is 20 degrees Celsius (Tyus, 1987). In lakes and reservoirs spawning has been observed in water depths as deep as 10 to 18 m, but most fishes spawn in less than 2 m of water. In riverine systems razorbacks spawn at an average depth of 0.63 m (U.S. Fish and Wildlife Service, 1998).
Spawning is the time when razorback suckers are most active, and they may travel anywhere from 0 to 112.7 km (Modde and Irving, 1998). When the fish reach their spawning grounds, they lie close to the bottom in large aggregates. When females become ready to mate they leave the group, followed by one or more males, and move to the bottom. After spawning takes place, which takes up to three minutes, the fish return to the group (U.S. Fish and Wildlife Service, 1998). Females may spawn repeatedly in an hour and/or on successive days. Modde and Irving (1998) concluded razorbacks spawn at more than one site, but this needs more study.
Breeding interval: The species breeds once per year, concentrated in the spring and summer.
Breeding season: The spawning season is variable across the species' range, but is generally from January through June, but has been documented both earlier and later.
Key Reproductive Features: seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (External ); oviparous
Xyrauchen texanus does not appear to provide parental care. Further research is needed to determine if there is any protection of the spawning depressions before the eggs hatch.
Parental Investment: pre-fertilization (Provisioning)
The razorback sucker (Xyrauchen texanus) is a suckerfish found in rivers and lakes in the southwestern United States and formerly northwestern Mexico. It can grow to 91 cm (3 ft) in length and is recognisable by the keel between its head and dorsal fin. It used to inhabit much of the Colorado River Basin but commercial fishing, river damming, habitat loss, and predation by non-native fishes have caused great declines in populations. It is now restricted to the Colorado River upstream of the Grand Canyon and to four reservoirs, Lake Mead, Lake Mohave, Lake Havasu, and Lake Powell.
It usually moves from deep water to suitable spawning grounds to breed, and research into its habits and breeding locations is ongoing. It has been a federally protected fish since 1991 and is rated as "Critically Endangered" by the International Union for Conservation of Nature, and Critically Imperiled by NatureServe. There are some signs of recovery, with fish being observed in the lower Grand Canyon in 2012 and 2013.[3]
The razorback sucker is most notable for the sharp-edged bulge on the anterior part of its back, between the head and dorsal fin, giving rise to its common name, as well as to the alternative name "humpback sucker".[4] The fish can attain lengths of up to 91 cm (3 ft)[5] and weights of 6 kg (13.2 lb).[4] A common length is 50 cm (1.6 ft).[5] The fish has an olivaceous to brown-black color on top grading to a lighter yellow below. Adult razorbacks are easily distinguished from other suckers by the predorsal keel.[4]
The species originally occurred throughout the medium-sized and large rivers of the Colorado River Basin, including to the states of Baja California and Sonora in Mexico, but its range has shrunk to the river above the Grand Canyon, and to Lake Mead, Lake Mohave, and Lake Havasu on the lower part of the river. It is also considered extirpated from Wyoming. The reason for the decline is largely due to habitat loss. The state of California designated it as endangered in 1974, followed by the United States government in 1991. A population of over 3,000 fish in Lake Mohave has been created by an augmentation program using fry that were produced naturally in the lake. In addition, reintroduction programs have released hatchery-raised fish into Lake Havasu, the Colorado River below Parker Dam, and the Verde River.
In 2012 and again in 2013, razorback sucker have been detected in the lower Grand Canyon. These were the first recorded sightings in the Grand Canyon National Park since the 1990s. In March 2014, in an effort to find out more about this wild population, nine tagged adult razorback sucker were released into the River Colorado below the Lava Falls. By tracking these fish, biologists hope to be able to detect the whereabouts of other spawning fish and assess their movements and how they use the habitat.[3]
In spring 2014 a new search for reproduction of the fish at Grand Canyon National Park resulted in the first finding of larvae for several decades. On nine of 47 sites, spawning Razorbacks were found.[6]
Populations in the Green and Colorado rivers upstream of Glen Canyon Dam have been reestablished through a stocking program [7] and stocked razorback suckers have consistently spawned and produced larval fish.[8]
As of 2021, the only self-sustaining population of razorback sucker is found in Lake Mead.[9]: 35711 While larval fish are found in other areas, indicative of successful spawning, recruitment (survival to adulthood) is not sufficient or even absent due to predation. Non-native predators of the razorback sucker include striped bass and flathead catfish in the Lower Colorado Basin and smallmouth bass, northern pike and walleye in the Upper Colorado Basin, with channel catfish present in the San Juan River subbasin.[9]
Razorback suckers are long-lived; older fishes have been estimated at more than 40 years. Both males and females mature at age four. Spawning occurs in late winter or spring when groups of razorbacks settle to the riverbed and release their gametes. The adhesive eggs become attached to the interstitial spaces in the gravel substrate. A single female is attended by two to twelve males, and the female will spawn repeatedly with several males.[10] Hatching success depends on water temperature, with complete mortality at temperatures less than 10 °C (50 °F).
Razorback suckers inhabit a diversity of areas from mainstream channels to backwaters of medium and large streams or rivers. They prefer to live over sand, mud, or gravel bottoms. Razorbacks feed on algae, insect larvae, plankton, and detritus. The eyes are receptive to parts of the UV spectrum, particularly that portion of the retina that receives light from below. The Razorback spends most of its life at depths where UV light cannot penetrate but they move into the shallows for breeding. In the shallows, males stake out a breeding territory and hover near the riverbed. When another male enters the breeding area, the defending male rolls his eyes downward to reveal the upper third of the eye generating a flash of reflected sunlight. The strongest reflected component of the flash lies in the UV spectrum. The intruding male, swimming overhead, can see the flash below and will shy away from it. The eye flashes are not visible from a distance underwater and can thus be used to signal intruding males without alerting predators. Females do not react to the eye flashes.[11]
The Razorback sucker was once common throughout the Gila River watershed regions of Arizona. Commercial fishing together with dam building decimated the fish stock, which were unable to breed due to lower water temperatures in the reservoirs while dams blocked their movement into smaller channels (Nabhan 1988:553). They are now federally listed (USFWS October 23, 1991) as an endangered species with provisions for the protection of its critical habitat. Ongoing conservation efforts are taking place throughout the Upper and Lower Colorado River Basins. The largest and most genetically-diverse population is found in Lake Mohave, Arizona/Nevada border.
Since 2012, special spring releases from Flaming Gorge Dam have been timed to coincide with the presence of larval razorback sucker in the Green River. These flows mimic a more natural hydrograph and allow larval razorback sucker to access off channel wetlands as nursery habitat.[12] These dam operations have proven successful with razorback sucker in wetlands regularly surviving past the larval stage and migrating back to the Green River. Subsequent encounters of fish tagged while emigrating from wetlands have documented limited recruitment to the adult population by wild spawned razorback sucker.[13]
In 2021, the Fish and Wildlife Service proposed to reclassify the razorback sucker as threatened, rather than endangered, under the Endangered Species Act.[9]
The razorback sucker (Xyrauchen texanus) is a suckerfish found in rivers and lakes in the southwestern United States and formerly northwestern Mexico. It can grow to 91 cm (3 ft) in length and is recognisable by the keel between its head and dorsal fin. It used to inhabit much of the Colorado River Basin but commercial fishing, river damming, habitat loss, and predation by non-native fishes have caused great declines in populations. It is now restricted to the Colorado River upstream of the Grand Canyon and to four reservoirs, Lake Mead, Lake Mohave, Lake Havasu, and Lake Powell.
It usually moves from deep water to suitable spawning grounds to breed, and research into its habits and breeding locations is ongoing. It has been a federally protected fish since 1991 and is rated as "Critically Endangered" by the International Union for Conservation of Nature, and Critically Imperiled by NatureServe. There are some signs of recovery, with fish being observed in the lower Grand Canyon in 2012 and 2013.
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