7112 - Laserfiche WebLink

Home Browse Search

J"'i. ' 155 miles below Davis Dam in Topock Gorge in 1968, and a number was taken directly below the dam. They are reported as locally abundant in lakes Havasu, Mohave, and Mead, but all the individuals are large, perhaps indicating low reproductive success. Reproductive activities have been observed, however, in the Colorado River impoundments (Douglas, 1952; Jonez & Sumner, 1954; Wood, in Minckley & Deacon, 1968). Spawning occurs along the shorelines or in bays. One female is attended by 2 to 12 males, and the group moves in circles less than two meters in diameter, randomly spiraling over the bottom. The males appear to "herd" a female by nudging with their heads and predorsal keels against her genital region. When a site is selected the female simply settles to the bottom, with a mate closely pressed to each side. Vibrations then commence that culminate in a convulsive finale, at which time gametes are presumably emitted. The three fish then move i forward and upward, leaving a cloud of silt and sand marking the spot of activity. Females spawn repeatedly with numerous males. The eggs are transparent and adhesive, attaching to the substra#e upon which they are deposited. Spawning activities occur from late winter (February as based upon gonadal condition of specimens taken in 1965) to early summer, and young have been taken along shorelines of Lake Mead in June (Miller, in Sigler & Miller, 1963). Foods eaten by razorback suckers in the lower Colorado River include algae and dipteran larvae (Jonez & Sumner, 1954). Specimens that I have examined from Lake Mohave had their intestinal tracts entirely filled with planktonic crustaceans in May. Feeding activities were observed in about six meters of water. The fish moved with their mouths projecting forward and with a "bouncing," up-and-down pattern produced by slow, alternating sweeps of the caudal fin. The pectoral fins were held stiffly extended, producing a plane effect, and little lateral movement of the head was evident, perhaps as a result of the keel-like, anterodorsal surface which may,act as a lateral stabilizer. Hubbs & Miller (1953) also noted plankton as food for Xyrauchen in riverine environments of the northern part of its range, and commented on the length and "fuzziness" of the gill rakers in the species, which "approach those of the presumably plankton-eating suckers comprising the genus Chasmistes ... __ The habitat of this fish appears to be more than a meter deep, often ~'` to more than 15 m in reservoirs, over bottoms of sand, mud, or gravel ~, Sigler & Miller (1963) noted that current was usually strong where adult razorbacks are taken, but testimony of older persons who knew the species ~` in the lower Salt and Gila rivers before they were dried, indicates that large adults tended to remain in eddies and backwaters, lateral to the strongest currents and often concentrated behind obstructions or in deep holes near cut banks or fallen trees. As noted above, young razorback suckers appear to travel in large schools along the margins of streams or reservoirs. ,