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and Horsethief State Wildlife Area. Numbers of progeny from these brood stock family lots that are in excess of those needed for production of the brood stock have already been designated as suitable for stocking in the Colorado and Gunnison rivers (Czapla 1997). Burdick et al. (1995) have already conducted a risk assessment associated with stocking and the stocking plan has already been approved for implementation by the Recovery Program Biology Committee. The modification proposed by this plan with respect to Burdick et al. (1995) are the stocking numbers proposed and stocking in an additional reach of the Colorado River (palisade to Stateline). A target biomass objective for razorback sucker of 5 % of the total fish community biomass in each of the river reaches designated was arbitrarily selected. The numbers of razorback sucker required to equal this biomass was estimated to be 475 fish/mile using average weight (550 gm) and length (350 mm) estimates for adult fish at maturity (Age 5). For each river reach, achievement of stocking objective would result in an adult population of 23,900 adult fish from ages 5-7, and 71,700 fish distributed over 150 river miles of three reaches in the Upper Colorado River subbasin. Interim management objectives (!MO) for razorback sucker (Lentsch et al. 1998) indicate at least 2,660 adult fish are necessary as an effective population size to maintain long tenn genetic diversity. Using a demographic model developed by Crowl and Bouwes (1998), simulation results show a mean population or subpopulation size of 5,300 razorback sucker <.:1:800 fish) are necessary to be 95 % confident the population will be maintained over a 100 year period. If one considers each of the three target river reaches designated in this plan as supporting a subpopulation, then the IMO objective for this subbasin would be up to 18,300 adult razorback sucker. The IMO population objective represents slightly greater than one percent of the fish community biomass estimated in Anderson (1997). Stocking of razorback sucker will interject an additional species into the existing fish community, and has the potential to induce changes in the relative abundance and biomass of these species' populations in each of the targeted reaches. The stocking numbers proposed are influenced by the following assumptions: 1) the upper Colorado River reach (Rifle to Debeque) from which biomass "estimates in Anderson (1997) were made was at carrying capacity. 2) the Upper Colorado River reach and the Gunnison River reach are similar with respect to this carrying capacity based on similar geohydrology and predominating native fish communities based on obsetved native/nonnative species relative abundance as described in Burdick (1995) and Anderson (1997). This similarity is also assumed to extend to the Palisade-Stateline reach of the Colorado River. 3) Adult riverine habitat is not limiting in the upper Colorado River reach for razorback sucker, and likely not limiting in the other two reaches. 7