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I I I I I I I I I I I I I I I I I I I BIOLOGICAL OPINION Status of the Species Colorado River from Hoover Dam to Davis Dam (including Lake Mohave to its full pool elevation) and Lake Havasu (to its full pool elevation). Critical habitat for the razorback sucker includes portions of the Colorado, Duchesne, Green, Gunnison, San Juan, White and Yampa Rivers in the Upper Basin and the Colorado, Gila, Salt and Verde Rivers in the Lower Basin. All critical habitat reaches were considered to be occupied at the time of designation. Within the project area, critical habitat includes the Colorado River from Pierce Ferry to Hoover Dam (including Lake Mead to its full pool elevation); Hoover Dam to Davis Dam (including Lake Mohave to its full pool elevation); and Parker Dam to Imperial Dam (including the 100-year floodplain). The designation of critical habitat for the Colorado River fishes highlighted two important issues for these species: (1) Specific problems with habitat have resulted in the extirpation of these species from most of their historic range. Areas considered for designation as critical habitat are evaluated against the constituent elements deemed essential to species conservation. The conservative definition of critical habitat includes only those areas undisturbed or unmodified, and therefore possessing all the constituent elements in the correct propo rtion, but this definition fails to address the existing situation of the Colorado River fishes. There is little aquatic habitat in the Colorado River Basin that has not been affected in some way by development activities. Thus the designated areas do not support all the constituent elements in the same way as an undisturbed system might. (2) The rangewide status of these species has been greatly impacted, The bony tail chub is almost functionally extinct, the razorback sucker is not far from that status. For these tw 0 species the immediate need to provide for the conservation of the species is to prevent extinction in the wild. For that reason, any location that contained even a remnant population of bony tail chub and razorback sucker was included in critical habitat designation. The management of such areas is crucial to ensuring that activities undertaken there do not adversely affect what is left of these populations. Large reservoirs such as Lakes Mead, Mohave and Havasu are not natural features of the Basin and do not represent historic habitat types, even though they are within the historic ranges of the species; but, these large reservoirs are where these two fish species have their last large populations. These reservoirs are now essential to the conservation of the species. Critical habitat determinations include analysis of those areas that may require special management considerations or protection. Post-designation management actions to improve the quality of the critical habitat to support the listed species is part of the survival and recovery processes. 44