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sub-basins of which the Southern Bonneville cutthroat trout (SB) occupied eight sub-basins or 89% sub-basin occupancy. The assessment indicates these eight sub-basins have occupied habitat for thirteen SB populations (11 stream and 2 lakes). An additional ten SB populations occur in one sub-basin outside the Bonneville Basin, the Upper Virgin River sub-basin (Table 2). Currently, SB populations occupy 50% of historic sub-basins being present in four of the eight sub-basins. Two of these upper Virgin River populations are considered remnant populations. Their occurrence has been purported to be as a result of introductions by early settlers into the area in the mid-to-Iate 1800's through a low-elevation, upper headwater transplant from the Bonneville basin (Behnke 1976, 1992). Another explanation may be a natural geologic stream capture event caused by volcanic activity within the last 2,000 years B.P. which diverted portions of the Grass Valley-Pine Valley area into the Santa Clara River watershed within the upper Virgin River sub-basin (Dale Hepworth, Utah Division of Wildlife Resources, personal communications 1996). Reports of early pioneer observa- tions of native trout in the upper Santa Clara River date back to 1863 (Miller 1961). Given the reported abundance by Miller, Hepworth speculates that there would not have been enough time for the trout to reach those numbers in such a short time period if the pioneers had recently transplanted them. Hepworth bases this on abundance and distribution data available for known SB populations (Hep- worth, personal communication, 1996). The remaining eight populations were transplants from the two remnant populations in the late 1980's-1990's. All SB transplant populations in the upper Virgin River have been replicated from existing pure populations within that sub-basin. Hepworth estimates that 25 historic stream miles occurred in the historic natural stream capture event. The cooperative program between the UDWR and Dixie NF for management and conservation of SB populations continues to be implemented (Hepworth, personal communication 1996, Schmidt et al, 1995, Duffield 1990). The assessment indicates an estimated 1,565 perennial stream miles historically occurred in the eight sub-basins (Table 6d). An estimated 492 stream miles (31%) historically occurred on NFS lands on four NF's. Current occupied habitat occurs on only 7.6% of NF historic habitat for the twenty-three SB populations on two NF's (Fishlake and Dixie NF's). The SB populations are not known to occur (thought to be extirpated) in historic habitat on the Uinta and the Manti-LaSal NF's in two middle Sevier River sub-basins (Tables 3,4,5). Based on historic stream mileage and current occupancy, the assessment indicated that SB populations have been extirpated on 98% of the basins historic stream miles and 91 % of NF historic stream miles. This includes the ten SB populations (remnant and transplants) occupying waters on the Dixie NF in the Upper Virgin River sub-basin as a result of a possible natural stream capture event. Historical references relating to SB population occurrence and distribution is available but largely qualitative (Hickman 1978). Observations of native cutthroat trout in streams were noted by early European explorers beginning in 1776, and continuing through the early years of exploration and settlement of Utah Territory in the mid-18oo's by government surveyors and Mormon pioneers (Cleland and Brooks 1983, Madsen 1910, Behnke 1960, Brooks 1989, Popov & low 1950). Scientific interest in protection and conservation of BCT subspecies led Dr. Robert Behnke, Colorado State University, to initiate surveys in the early 1970's to document occurrence and distribution of BCT in the Bonneville Basin (Behnke 1973). The author began similar investigations at the urging of and in cooperation with Dr. Behnke in the early 1970's along with other federal and state biologists. These joint investigations led to increased discoveries of and management for BCT populations (Duff et aI. 1974, May 1977, May et al. 1978, Hickman 1978, Behnke 1973, 1978, Schmidt et al. 1995). In 1973, only three BCT populations were known to occur in southern Utah, one occurring in the Beaver sub-basin (Fishlake NF) and two in the Upper Virgin River sub-basin (Dixie NF). These three populations accounted for only seven stream miles of which the one population within the Bonneville 51