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near Littlefield, which includes the area where the Beaver Dam Wash connects with the <br />mainstem in Arizona (Golden and Holden 2005). The higher abundance of Virgin River <br />chub in these reaches may be attributed to constant flows created by natural springs (S. <br />Meismer, Virgin River Resource Management and Recovery Program or VRRMRP, <br />personal communication). In 2004, population estimates for the core area in Utah were <br />3,209 for chub larger than 150 mm (95% confidence interval of 2,496-4,203) and 4,996 <br />for chub smaller than 150 mm (95% confidence interval of 4,221-5,971) (Golden and. <br />Holden 2005). The 2004 estimate for the Arizona core area was lower, with 369 chub <br />larger than 150 mm (95% confidence interval of 314-449). There is little information <br />available on the movement of Virgin River chub. Adults and other life stages have been <br />found to move downstream (Virgin River Fishes Data Base unpublished data, as cited by <br />USFWS 1994), however the extent of upstream movement is unknown (USFWS 1994) <br />and limited by agricultural water diversions and artificial fish barriers (S. Meismer, <br />VRRMRP, personal communication). <br />The federal listing of Virgin River chub as endangered was based on "restricted <br />distributions, loss of significant portions of historical range and deterioration of much of <br />the remaining habitats" (USFWS 1994). The main factors contributing to the decline of <br />the species included alterations to the hydrology of the river system, and the introduction <br />of non-native species, particularly red. shiner (Cyprinella Iutf-ensis). <br />The final rule listing the Virgin River chub as endangered excluded the population <br />in the Moapa River (54 FR 35305). At the time of listing, this population was classified <br />as an undescribed subspecies of roundtail chub (G. robusta spp.). DeMarais et al. (1992) <br />used morphology, allozymes, and mtDNA haplotypes to determine that the