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Assuming an average annual survival rate of about 0.1 in age 0 to 3 fish (Valdez and Rye11995), this translates into an annual wild production of -50,000 age-O fish per year. Thus, removing about 960 to 1,400 age-O fish on an annual basis (to arrest decline) might be the equivalent of removing 2 to 3% of the annual age-O production. Removing 4,300 to 6,350 age-O fish per year (to achieve a positive increase to 1990 levels) might be the equivalent of cropping 9 to 13% of the annual wild production. As explained above, the model does account for this cropping in estimating the projected future stock. Also as explained above, this cropping may need to be doubled to account for post- release mortality. Finally, we caution that annual production of age-O fish in the LCR is likely highly variable (in part because of the highly stochastic nature of the LCR), and that this approach assumes a 0.1 survival rate during the first year of life (based on Valdez and RyeI1995). Thus in some years, the cropping may be insignificant, while in other years it could be significant (i.e., > 10%), depending on the goals to be achieved. Where and when will fish be released back into the wild? There appear to be two general approaches that can be taken for stocking fish back into the wild once the desired growth has been obtained at whatever facility is ultimately selected and funded for the propagation effort. Namely, release into the LCR or release into the mainstem Colorado River. Release of fish into other small tributaries in Grand Canyon could be a third option; however, this approach should not be expected to solve the primary problem of lack of recruitment in the LCR population. In addition, until problems with predators are dealt with in these other tributaries, this approach may largely be a waste of resources. Problems with release of fish back into the LCR may be primarily associated with carrying capacity of the LCR, and potential for impacting the resident wild population. Table 3 shows fall population abundance estimates that have been obtained in the LCR for fish> 150 mm. These estimates are thought to estimate the number of humpback chub that "overwinter" in the LCR, and may be somewhat representative of the carrying capacity in this system. Consider if only 768 to 1,131 (Table 2) humpback chub> 150 mm were released into the LCR each fall in an attempt to arrest further decline. Also consider that the average point population estimate for humpback chub> 150 residing in the LCR during the fall since 1992 is 1,729 fish (Table 3). This translates into a 44 to 65% increase in numbers of fish that would suddenly inhabit the system. Should 3,435 to 5,086 fish be released in an attempt to reach 1990 age-4+ levels, this translates into a 199 to 294% increase. If food is limiting in the LCR, there is concern that the sudden increase in abundance of humpback chub> 150 mm could cause secondary effects related to carrying capacity and density dependence, cropping the next year's age-O cohort via predation and potentially eliminating any gain from the augmentation effort. Another obvious concern would be the accidental introduction of diseases or parasites into the wild, again potentially negating positive effects. One positive aspect of releasing supplemental fish back into the LCR could be gaining immediate familiarity with habitat, breeding grounds, and migration routes. 31