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Implementation of this approach carries the following assumptions: ~ 1) Numbers of razorback sucker to be stocked are adequate to establish a minimum viable population in the Green River that will provide for adequate reproduction and recruitment into the aduh population to sustain itself. The current approach is not designed to maintain the minimum viable population. ~ 2) Other recovery efforts of the RIP (e.g., flow recommendations, flood plain reacquisition, nonnative control) will provide for effective augmentation/reintroduction of the Green River razorback sucker population. Implementation of this approach carries the following inherent risks: 1) Genetic risks could include outbreeding or inbreeding depression and/or interspecific hybridization Outbreeding and 'inbreeding depression of razorback sucker are addressed in the Genetics Management Plan Continuing to follow the guidance of the Genetics Management Plan (e.g., use of 25x25 mated pairs, stocking equal family lots; Czapla ~ 1999) should reduce the risk of either of these problems. An increased number of razorback suckers in the Green River may result in hybridization with native flannehnouth and bluehead suckers and with nonnative white suckers. This could lead to a loss of interspecific genetic identity. Flannehnouth and razorback suckers ~ hybridize m the wild (Huth et al. 198?) as do flannelmouth and bluehead suckers (Ryden and Pfeifer 1995) but hybridization rates are low. Stocking hatchery-reared razorback suckers is not expected to increase the rate of hybridization between these species of native suckers (Burdick 1992). Flannehnouth and bhiehead suckers hybridize with the nonnative white sucker (Ryden and Pfeifer 1995; 1996a and 1996b). Thus, razorback ~ sucker may also hybridize with white sucker. 2) Ecological risks could include pathogen and/or parasite transmission, competition and/or predation, and chenwreceptive inoprinting. Pathogens and parasites (i.e., Asian tapeworm) harbored by hatchery reared fish could adversely impact wild fish populations. A resistant ~ broodstock may transmit pathogens into wild populations of razorback sucker or other sensitive or endangered species, which may have little or no resistance. To reduce the risk of pathogen and parasite transmission, inspections are conducted by the Fisheries Experiment Station (UDWR) to ensure that culture facilities and stocked razorback lots are specific pathogen free and meet the requirements of the Fish Health Policy Board. ~ Hatchery-reared fish may compete for food and habitat with other native fish species, particularly flannehnouth and bluehead suckers. Stocking large numbers of razorback suckers into the Green River may cause shifts in habitat use, distribution, and abundance of these species. ~ Several studies have documented predation on larval and small razorback sucker by channel catfish, common carp, green sunfish, red shiner, and fathead minnow (Marsh and Brooks 1989; Hinckley et al. 1991; Ruppert et al. 1993; Gutermuth et aL 1994; Tyus and Saunders 1996). Stocking larger sized razorback suckers (at least 300 xnm TL in size) may ~ 5