Razorback sucker
Encyclopedia
The razorback sucker, Xyrauchen texanus, is an endangered fresh water sucker
Catostomidae
Catostomidae is the sucker family of the order Cypriniformes. There are 80 species in this family of freshwater fishes. Catostomidae are found in North America, east central China, and eastern Siberia...

 of rivers in the Colorado River
Colorado River
The Colorado River , is a river in the Southwestern United States and northwestern Mexico, approximately long, draining a part of the arid regions on the western slope of the Rocky Mountains. The watershed of the Colorado River covers in parts of seven U.S. states and two Mexican states...

 drainage of western North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

.

Description

The razorback sucker is most notable for the sharp-edged bulge on the anterior part of its back, between the head and dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...

, giving rise to its common name, as well as to the alternative name "humpback sucker". The fish can attain sizes of up to 1.0 m (3.3 ft) and weights of 6.0 kg (13.2 lb) 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.

Distribution

The species originally occurred throughout the medium-sized and large rivers of the Colorado basin, but its range has shrunk to the river above the Grand Canyon
Grand Canyon
The Grand Canyon is a steep-sided canyon carved by the Colorado River in the United States in the state of Arizona. It is largely contained within the Grand Canyon National Park, the 15th national park in the United States...

, and to Lake Mead
Lake Mead
Lake Mead is the largest reservoir in the United States. It is located on the Colorado River about southeast of Las Vegas, Nevada, in the states of Nevada and Arizona. Formed by water impounded by the Hoover Dam, it extends behind the dam, holding approximately of water.-History:The lake was...

, Lake Mohave
Lake Mohave
Lake Mohave is a reservoir formed by Davis Dam on the Colorado River, which defines the border between Nevada and Arizona in the United States. The lake lies at an elevation of near Laughlin, Nevada, Searchlight, Nevada, Cottonwood Cove, Nevada, and Bullhead City, Arizona, about downstream from...

, and Lake Havasu
Lake Havasu
Lake Havasu is a large reservoir behind Parker Dam on the Colorado River, on the border between California and Arizona. Lake Havasu City sits on the lake's eastern shore. The lake has a capacity of . The concrete arch dam was built by the United States Bureau of Reclamation between 1934 and 1938...

 on the lower part of the river. The reason for the decline is largely due to habitat loss. The state of California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

 designated it as endangered
Endangered species
An endangered species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters...

 in 1974, followed by the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 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
Parker Dam
Parker Dam is a concrete arch-gravity dam that crosses the Colorado River downstream of Hoover Dam. Built between 1934 and 1938 by the Bureau of Reclamation, it is high, of which are below the riverbed, making it "the deepest dam in the world". The dam's primary functions are to create a...

, and the Verde River
Verde River
The Verde River is the north and northwestern watershed of the Salt River–Verde River Watershed that co-join and enter the Gila River at Phoenix, Arizona, located in the U.S. state of Arizona...

.

Biology

Razorbacks 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. Spawning takes place in a group settling to the bottom and releasing their gametes. The adhesive eggs become attached to the interstitial spaces in the gravel substrate. A single female is attended by 2 to 12 males, and the female will spawn repeatedly with several males. 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 larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...

e, plankton, and detritus. The eyes are receptive to parts of the UV
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

 spectrum, particularly that portion of the retina
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...

 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
Territory (animal)
In ethology the term territory refers to any sociographical area that an animal of a particular species consistently defends against conspecifics...

 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.

Conservation

The razorback sucker was 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
Lake Mohave
Lake Mohave is a reservoir formed by Davis Dam on the Colorado River, which defines the border between Nevada and Arizona in the United States. The lake lies at an elevation of near Laughlin, Nevada, Searchlight, Nevada, Cottonwood Cove, Nevada, and Bullhead City, Arizona, about downstream from...

, Arizona-Nevada. Recovery efforts are controversial because the sucker is not considered a food or sport fish, conflicts with sport fishermen, have seen little to no progress, and are very expensive.
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