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Table 3 cont. Common Name Scientific Name Status Montane meadow mouse Sedge Virgin River thistle Beaver Dam milk vetch Utah Chaetarthria water scavenger beetle Microtus montanus rivularus Candidate 2 Carex haysii Candidate 2. Circium virginensis Candidate 2 Astragalus geyeri var. Candidate 2 triquetrus Chaetarthria utahensis Candidate 2 MacNeill sooty wing skipper Hesperopsis ~racielae Candidate 2 contribute to a species' conservation, however, not all areas proposed as critical habitat may be necessary to prevent extinction. Consequently, some areas or portions of areas may be excluded due to economic considerations, provided that such exclusions would not result in the extinction of the species. Species conservation is related to a number of factors, such as the number of individuals, the amount of habitat, the condition of the species and its habitat, the species' reproductive biology, and the genetic composition of the remaining populations. Many of these factors cannot be determined in a short period of time, especially for wide-ranging or long-lived species. In its designation of critical habitat for the Virgin River fishes, the Service has attempted to conserve habitat for recovery of each species, identifying reaches that contain habitat features needed for spawning, rearing, feeding, and migration. Throughout its previous efforts (e.g., section 7 consultation, research}, the Service has also identified biologically important areas that still contain these listed fishes. Additionally, important reaches have been identified in the Virgin River Fishes Recovery Plan. Although all areas proposed are important to conservation, those areas currently supporting the largest remaining populations may be key to the long-term survival of these species. Additionally, the physical and ecological relationships between these areas is an important consideration. Extinction of these endemic fishes would most likely occur as a result of the presence and continued introductions of nonnative fishes, significant changes in the hydrologic regime, increased fragmentation and channelization, and decreased water quality. Although a single action could result in extinction, the cumulative reduction in suitable habitat resulting from many actions could also lead to species' extinction. The exclusion analysis focuses not only on specific reaches, but also their relationship to other reaches, to evaluate whether or not extinction would be probable if a reach were excluded. Such factors as (1) current population status, (2) habitat quality (e.g., presence of spawning sites, nursery areas, and 28