7970 - Laserfiche WebLink

Home Browse Search

suckers at DNFH was obtained in 1981-82 from Lake Mohave, a mainstem impoundment on the Colorado River, Arizona-Nevada, created in 1954 by closure of Davis Dam. The reservoir consists of an upstream riverine reach approximately 60 km in length, which grades into a wider (maximum width 6.4 km) lower basin 48 km long. It has a surface area of 115 km2, average depth of 10.5 m (maximum approximately 43 m), and a volume of 2.3 x 109 m3 at full pool (197 m above MSL). Retention time is short, with total replacement taking only 0.24 year at an average annual discharge of 9.3 x 109 m3. Tag-recapture data indicate a population of less than 55,000 adult razorback suckers in the reservoir (Marsh, 1994). Although scattered throughout, the fish are concentrated in upper parts of the lower basin. They are most vulnerable to capture when aggregated near shore for spawning in winter-spring, but not as readily collected when dispersed at other times. The species has made up 10-30% of net catches in spawning areas over the past 20 years (Hinckley, 1983; Hinckley et al., 1991). Production of hatchery year classes.- Development of procedures to culture razorback suckers began with Toney (1974), were refined by Inslee (1982) and Hamman (1985}, and soon became routine (Hinckley et al., 1991). Adult fish are held in outdoor ponds and transferred to indoor holding facilities in spring for spawning. Ovulation is induced by intramuscular injection of human chorionic gonadotropin (up to three 220 IIJ per kg injections at 24-hour intervals). When necessary to induce or maintain milt production, males are injected with 660 IU common carp (Cyprinus carpio) pituitary extract. Ova are hand-stripped into water, sperm from two or three males is added, and the nnixture gently stirred. After addition of bentonite to counteract adhesion, fertilized ova are rinsed in fresh water and allowed to harden for about 0:75 hour in floating Nitex®-mesh baskets. Developing embryos are transferred to flow-through (18-22°C), HeathC~incubator 17