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MAINTAINING RAZORBACK SUCKER IN LAKE MOHAVE tion and management of sport fishes may have been the decisive factor in the razorback sucker's decline. Options available to the NFWG were few. Mean- ingful habitat restoration or the removal of nonna- tive fish from Lake Mohave and other upstream portions of the river basin are unlikely. We thought the only feasible approach was to stock fish large enough to ensure some survival. Razorback suckers are reared successfully and grow rapidly. Unfortu- nately, the costs of raising and transporting thou- sands of large razorback suckers from Dexter Na- tional Fish Hatchery (1,100 km) or other existing fish culture facilities would be high. Experiments conducted in the mid-1980s showed that razorback suckers spawned and produced young if provided habitats free of nonnative fishes (Minckley et al. 1991). We believed a razorback sucker of 25-30 cm TL was large enough to escape most predators, and we chose that size as the target for stocking. Fish would be grown to this length, implanted with pas- sive integrated transponder (PIT) tags, and released into the reservoir. A minimum of 10,000 young razorback suckers would be released over 5 years. Arizona State University has conducted an ongoing reservoir monitoring program for nearly 20 years, and this continuing monitoring program will pro- vide the information necessary to determine stocked fish survival. Stocking will be refined as data become available. Development of Rearing Areas Aerial photographs and surveys identified several potential rearing sites along Lake Mohave's shore- line. The reservoir has several naturally occurring backwaters that seasonally become isolated from the main reservoir. These ephemeral backwaters and coves that easily could be closed were visited, prioritized, and surveyed. Few coves were suitable for rearing because of their size or the expense to make them suitable for rearing razorback suckers. Alternative rearing sites away from the reservoir were also examined. Five specific types of potential rearing areas have been identified or are being used. They include ephemeral backwaters, backwa- ters closed by net, permanent backwaters, hatchery facilities, and outlying ponds. Since 1990, nine small ephemeral backwaters (0.1-0.8 ha) have been developed as seasonal rear- ing areas. These shallow backwaters are seasonally closed to the main reservoir by gravel berms formed by wave-induced beach erosion and deposition. Berms prevent fish passage, but backwaters remain hydraulically connected to the reservoir. Backwa- 129 ters are seasonally flooded and drained as the res- ervoir is operated within its 5-m-vertical-fluctuation zone. Backwaters are normally flooded from spring through late summer and drained in autumn as the reservoir is lowered to develop storage for spring runoff. Drainage prevents the establishment of res- ident fish populations and assists in the recovery of reared fish. Growth-rate information provided by Dexter Na- tional Fish Hatchery suggested 25-cm razorback suckers could be raised in 18 to 24 months; there- fore, permanent (year-round) rearing areas were desirable. Ephemeral backwaters would be used for rapid seasonal growth, but fish less than 25 cm would have to be moved to a deeper, permanent- water cove in autumn when the reservoir elevation dropped. Davis Cove provided a potentially excel- lent rearing site because of its size, shape, and depth. The cove has a maximum depth of 4 m at minimum reservoir pool, a narrow entrance, and a surface area of 1.2 ha. The cove's entrance was closed in 1991 using a 10-mm-bar-mesh net and a flotation boom. The net conformed to the entrance and accommodated the reservoir's 5-m fluctuation zone. This temporary barrier was used for 3 years and was replaced with an earthen berm in fall 1994. Willow Beach National Fish Hatchery is a cold- water trout hatchery located on Lake Mohave, 16 km downstream from Hoover Dam. The facility is currently adding water heaters that will allow the hatchery to hatch and rear razorback sucker. Race- way operations are being modified to rear 5-15-cm (TL) razorback suckers. We plan to test the concept of stocking backwaters with larger juveniles in order to reduce the number of fish smaller than 25 cm at the end of the growing season. This approach could help optimize survival, production, and fish growth while reducing the need to transfer, hold, and han- dle fish smaller than 25 cm. Razorback suckers have been reared successfully elsewhere (Minckley et al. 1991). The option of rearing fish away from Lake Mohave in city park ponds, golf course ponds, and housing development lakes is being explored. A Memorandum of Agree- ment was recently signed between the Bureau of Reclamation and City Manager of Boulder City, Nevada. Under the agreement, razorback suckers have been stocked in a municipal golf course pond. Propagation and Rearing The Lake Mohave project is unique among en- dangered fish stocking programs because of the range of methods available to produce young fish.