| Razorback sucker | |
|---|---|
| Conservation status | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Cypriniformes |
| Family: | Catostomidae |
| Genus: | Xyrauchen C. H. Eigenmann & Kirsch in Kirsch, 1889 |
| Species: | X. texanus |
| Binomial name | |
| Xyrauchen texanus (C. C. Abbott, 1860) |
|
The razorback sucker, Xyrauchen texanus, is an endangered fresh water sucker of rivers in the Colorado River drainage of western North America.
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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". The fish can attain sizes of up to 1.0 m (3.3 ft) and weights of 6.0 kg (13.2 lb) [1] 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. [2]
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, and to Lake Mead, Lake Mohave, and Lake Havasu on the lower part of the river. 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.
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. [3] 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.[4]
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, 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.