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population sizes needed to maintain populations of domestic animals or captive populations for a number of generations have been determined, minimum population sizes needed to maintain wild species are less well understood. Target population sizes for populations of the endangered big-river fishes used in this document were provided by the Colorado River Fishes Recovery Team and accepted by USFWS. These population numbers represent the best professional judgement and fall within the range of "...several thousand to 10,000..." thought to provide minimum viable population sizes to sustain wild populations (reviewed by Thomas 1990). However, more specific population targets are being developed for portions of the upper Colorado River basin (e.g., Crowl and Bouwes 1997). At present these target sizes are preliminary and have not been accepted by USFWS. Recovery plans can be updated as necessary when final population targets are developed and accepted. It is anticipated that it will take several years before such numbers are finalized. Although population targets must be based on genetic requirements, they also must consider how the population viability of wild populations are affected by existing conditions and how they might be threatened by new changes. Ecosystem RecoverX The USFWS and NMFS (1994) has identified ecosystem recovery as an integral part of endangered species recovery program and the USFWS funded preparation of a draft multi-species recovery plan for the Colorado River fishes in 1996. This multi-species plan is preliminary and has not been approved by the Colorado River Fishes Recovery Team. However, it is assumed that a multispecies or ecosystem recovery plan will eventually be forthcoming. Critical habitat designation will play an important role in maintaining the natural ecosystem. However, as important as critical habitat determination and management has been as a recovery tool, there is still a need for management of the riverine ecosystem due to widespread, continuing anthropogenic changes. Single species recovery remains important, but continuing habitat change and the complexity of riverine ecosystems suggest that recovery of the endangered Colorado River fishes should also include a more holistic approach. 34