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2. Areas where juvenile razorback suckers. have been collected or which could provide suitable nursery habitat (backwaters, flooded bottomlands, or coves). 3. Areas presently occupied or that were historically occupied that are considered necessary for recovery and that have the potential for establishment of razorback sucker. 4. Areas and water required to maintain rangewide fish distribution, and diversity under a variety of physical, chemical, and biological conditions. 5. Areas that need special management or protection to ensure razorback survival and recovery. These areas once met the habitat needs of the razorback sucker and may be recoverable with additional protection and management. RESULTS OF APPLYING PRIMARY CONSTITUENT ELEMENTS AND SELECTION CRITERIA The primary constituent elements were used to determine critical habitat throughout the historical range of the Colorado River endangered fishes. In addition, the five selection criteria described above were also used to evaluate potential razorback sucker critical habitat areas. The proposed critical habitat designations are based on the primary constituent elements, published and unpublished sources, Service reports and other findings, recovery plans (for Colorado squawfish, humpback chub, and bonytail chub), additional selection criteria, and the preliminary recovery goals being presently discussed for the razorback sucker by the Colorado River Fishes Recovery Team. The presence of one or more primary constituent elements or additional selection criteria did not automatically result in inclusion as proposed critical habitat. Rather, the relative value of each constituent element for the survival and recovery of each fish was also evaluated for each reach. In accordance with Section 3(5)(c) of the Act, which states that: "Except in those circumstances determined by the Secretary, critical habitat shall not include the entire geographical area which can be occupied by the threatened or endangered species." Generally, the entire historical range of the fish should not be designated as critical habitat. Selection criteria number 4 was used to maximize the diversity of the selected reaches. As discussed above under Constituent Elements-Physical Habitat, inundated floodplains (bottomland habitats) are important for razorback sucker and Colorado squawfish. These wooded bottomlands, side and secondary channels, oxbow lakes, and floodplain wetlands provide nutrients, food, cover, and other features necessary for various life stages of these fishes. In order to delineate such areas in designating critical habitat, the Service is using the 100-year flood elevation (100-year floodplain). In no way is this meant to include all land within the 100-year floodplain as critical habitat, nor does it imply a specific frequency of flooding will be required as part of the rule. Only those areas which provide one or 40