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130 MUELLER Some methods optimize production, whereas other techniques produce fewer fish but focus on genetic diversity. The following propagation methods have been or currently are being tested. (1) Backwaters were stocked with mature adults from the reservoir prior to the spawning season. Adults were stocked at a ratio of one female to two males. Males were stocked in larger numbers because females normally spawn with multiple males at one time (Minckley 1973). Adults were recaptured and returned to Lake Mohave following spawning. A different spawn- ing group was used each year. (2) Another approach was examined to reduce spawner handling and stress associated with allowing fish to spawn in the backwaters and eventually recap- turing and returning them to the reservoir. Spawning fish were collected from Lake Mohave in 1993, gametes were stripped, eggs were fertilized, and fish were re- turned to the reservoir. The egg contribution from each female was fertilized by at least two males. About 250,000 eggs from 24 females and about 60 males were collected; 200,000 were dispersed in Yuma Cove, and the remainder were hatched in the laboratory for larval research. Unfortunately, the reservoir dropped about 1 m shortly after the eggs were distributed in Yuma Cove. (3) Larvae are phototactic and can be captured easily at night by using lights. Naturally spawned reservoir larvae have been collected for a number of years using handheld spotlights and small dip nets or light traps (Minckley et al. 1991; Mueller et al. 1993). These tech- niques are being refined to collect large numbers of larval razorback suckers for stocking into the backwa- ters. (4) Dexter National Fish Hatchery is the USFWS warmwater, endangered-fish culturing facility. The hatchery maintains a broodstock of Lake Mohave ra- zorback sucker and produces fish for scientific research and stocking. The hatchery supplied 10,000, 6-cm (TL) fish for Davis Cove on 28 June 1992. All backwaters except Davis Cove were poisoned to remove nonnative fish. Davis Cove was not poi- soned due to its close proximity to a large public marina and in order to test if razorback suckers could survive in a cove where nonnative fish were reduced but not eliminated. Here the nonnative fish community was reduced using gill and trammel nets and by electrofishing. Stocking Criteria Lake Mohave contains several piscivores, includ- ing striped bass Morone saxatilis, largemouth bass Micropterus salmoides, bluegill Lepomis macrochi- rus, and channel catfish. The stocking-size criterion was based on the assumption that most piscivores would have difficulty consuming a 25-cm razorback sucker. This criterion will be refined as survival rates of recaptured fish are developed. Currently, razorback suckers longer than 25 cm that are taken from the rearing areas are tagged with PIT tags and stocked directly into the reservoir. Smaller fish are moved to a permanent backwater and allowed to continue their growth. Monitoring Larval and juvenile fish are collected using lights and small dip nets, light traps, small-mesh seines, fish traps, small-mesh trammel nets, and electro- fishing. Ephemeral backwaters and Davis Cove are sampled bimonthly to monitor fish survival, growth, and condition. Piscivorous fish collected in Davis Cove during sampling events are removed. Arizona State University has been monitoring the reservoir's razorback sucker population for nearly 20 years. The reservoir is sampled specifically for razorback suckers during spring and Thanksgiving class breaks. This effort has been intensified during the past 8 years to estimate the population size. Sampling is conducted in March when spawners are concentrated in shallow water and are vulnerable to trammel nets, large beach seines, and electrofishing. Usually 1,000 to 2,000 adults are collected and tagged with PIT tags annually. The spring and fall monitoring efforts are providing the information required to determine the survival of backwater- reared fish. Results Propagation and Rearing In January 1991, 100 (33 females, 67 males) adult razorback suckers were stocked into Yuma Cove just prior to spawning season. Larvae were collected during the spawn; however, for reasons unknown, no young fish survived. A similar effort was at- tempted in January 1992 with 88 adults (28 females and 60 males), and 296 young fish were recovered (Table 1). Juveniles collected in November 1992 averaged 35.4 cm TL (maximum 39.1 cm). One hundred fifty-three fish larger than 25 cm were tagged with PIT tags and released in Lake Mohave; the remainder (<25 cm) were placed in Davis Cove to continue their growth. Fifteen juveniles were sacrificed for genetic (mitochondrial DNA and al- lozyme) analyses to determine the number of fe- males that actually contributed to the 1992 year- class. Results showed that although 28 females were introduced, the 15 juveniles were produced by 5 females, and 8 were produced by a single female (T. Dowling, Arizona State University, personal communication). The 1993 fertilized egg experiment produced 17