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548 MARSH ET AL. listing as endangered, efforts began to reintroduce or augment razorback sucker populations by stock- ing millions of hatchery-produced and hatchery- reared larvae and juveniles into the lower Colorado River and central Arizona rivers from which the species was extirpated (Minckley 1983; Minckley et al. 1991; Hendrickson 1993). However, this ap- proach proved ineffective because predation by nonnative fishes was extreme and long-term post- stocking survivorship was nil (Marsh and Brooks 1989; Hendrickson 1993). Largely because of this program's failure, the razorback sucker was listed in 1991 as an endangered species (USFWS 1991). A cooperative partnership was established in 1990 to conserve the razorback sucker in Lake Mohave, and the group became known as the Na- tive Fish Work Group (NFWG). Its members in- clude Arizona Game and Fish Department, Ari- zona State University, U.S. Bureau of Reclama- tion, U.S. Fish and Wildlife Service, U.S. Geo- logical Survey, U.S. National Park Service, and Nevada Division of Wildlife. The NFWG devel- oped several research and management strategies for sustaining razorback suckers in Lake Mohave but determined that stocking at a size relatively safe from predation was the only way to ensure success (i.e., survival) and thereby supplement al- ternative strategies (i.e., habitat restoration and nonnative fish removal; Mueller 2003). The group's goal was to establish a repatriate popu- lation of 50,000 fish that adequately represented the known genetic characteristics of the wild Lake Mohave population that existed when its decline began. Throughout this paper, "wild" refers to the naturally produced adults and larvae, and "repa- triate" refers to fish derived from wild stock, reared in captivity, and stocked into the reservoir. Based in part on the work of Marsh and Brooks (1989), the initial target size at release was 250- 300 mm total length (TL), which required sub- stantial quantities and reliable sources of larvae and predator-free rearing environments. One so- lution was to spawn broodstock maintained at hatcheries and rear their larvae, but hatcheries were generally space-limited and cost-prohibitive, and razorback suckers require up to 2 years to attain the target size. Hatchery-produced fish also would under-represent the genetic diversity of the razorback sucker population in Lake Mohave (Minckley et al. 1991; Dowling et al. 1996b; Minckley et al. 2003). The group instead explored options to produce larvae in seminatural environ- ments such as lakeside backwaters or offsite ponds, but early production efforts afforded little success. That is, approximately 200 wild adult ra- zorback sucker stocked into a lakeside backwater before the 1991-1992 spawning season produced fewer than 300 juveniles, and stripping gametes, fertilizing eggs, and releasing 200,000 embryos into a lakeside backwater produced only 17 ju- veniles from 1991 to 1993 (Minckley et al, 1991; Mueller 1995). An alternative effort began in 1994 when collection methods were honed to gather nat- urally produced larvae from inlets and bays around Lake Mohave (see Mueller et al. 1993). To date this effort has yielded more than 440,000 larvae. These larvae were reared in protected lakeside backwaters and offsite growout facilities that were free of nonnative predators, and after achieving a nominal target size, the juveniles were measured, PIT-tagged (passive integrated transponder; Bio- mark, Inc., Meridian, Idaho), and repatriated to the lake. Monitoring of the NFWG's repatriation program in Lake Mohave has coincided, to date, with an- nual assessments of the lake's wild razorback suck- er population, which began in the early 1970s un- der the direction of W. L. Minckley at Arizona State University. This sampling effort has pro- duced repatriate population estimates that have been occasionally reported along with the status of the wild population (e.g., Minckley et al. 2003), but overall success or failure of the group's goal to repatriate a population of 50,000 razorback suckers was not evaluated. However, the program has achieved success because the genetic charac- teristics of the wild population have been passed along from adults to the repatriate larvae (Dowling et al., 2005). In this paper, we present population abundance, survival, and growth rate estimates of the NFWG's razorback sucker repatriation pro- gram from 1992 through 2002; assess the suc- cesses and failures of the program from a demo- graphic perspective; and offer recommendations. Methods Once they attain adulthood, repatriated fish were available for capture as they commingled with wild razorback suckers on spawning grounds in the spring. Annual spring (March) censuses of adults in Lake Mohave coincided with peak razorback sucker reproductive activity when fish were ag- gregated in coves and inlets, and along shallow shorelines, reefs, and spits (Minckley 1983). Less intensive monitoring also occurred at nonspawn- ing times of year. Trammel nets (20-100 m long x 3 m deep, 2.5-3.8-cm inner mesh, and 25.4- 30.5-cm outer mesh) and boat-mounted electro- fi tl