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Feasibility of Expanding the Humpback Chub Population Via Translocation in the Little Colorado River or other Grand Canyon Tributaries The biological factors necessary to establish a second population in Grand Canyon have previously been addressed (Valdez et al. 2000). Although tributaries were not deemed optimal for establishment of a second population of humpback chub (Valdez et al. 2000), further investigation may be of value. Specifically, we explore the feasibility of transplanting fish above Chute Falls (i.e., above 14.9 km) in the LCR, and establishing (or augmenting) fish in Bright Angel, Shinumo, or Havasu creeks. Translocation is the intentional release of animals into the wild in an attempt to establish, reestablish, or augment a population (World Conservation Union 1987); and in the face of increasing extinction rates, translocations of rare species may become an important conservation tool (Minckley 1995, Griffith et al. 1989). A number of variables are known to influence the probabilities of success for translocation efforts (Griffith et al. 1989). Theoretical considerations predict that population persistence will be higher if the number of founders is large, the rate of population increase is high, and the effect of competition is low (Wilson 1988). Other factors that may enhance persistence are: 1) low variance in rate of increase, 2) reduced environmental variation (Leigh 1981), 3) presence of refugia (Goodman 1987), and 4) and high genetic diversity among founders (Stockwell and Leberg 2002). In addition, Griffith et al. (1989) found that the increase in success associated with releasing larger numbers of animals quickly becomes asymptotic (i.e., a threshold is reached beyond which the release of more organisms does little to increase the likelihood for success). Griffith et al. (1989) also point out that the chance for a successful translocation increases if there is more than one potential translocation area, and that substantial gain is achieved by splitting the animals between areas. Translocation of humpback chub within the Little Colorado River Rationale In a December 6,2002 Biological Opinion (USFWS 2002b), and through subsequent Section 7 re-initiation in March 2003, a conservation action was proposed by U.S. Bureau of Reclamation, Grand Canyon National Park, Glen Canyon National Recreation Area, and GCMRC to translocate three hundred 50 to 100 mm total length humpback chub from near the mouth of the LCR to a reach within the LCR above a natural travertine dam structure referred to Chute Falls (14.9 km). Since results of the translocation effort in July 2003 were deemed successful (i.e., translocated fish were found to survive; Stone and Sponholtz 2003), a second translocation of 300 humpback chub will be conducted in summer 2004. The action is intended to serve as mitigation for the possible effects resulting from experimental flows from Glen Canyon Dam, and from mechanical removal of rainbow trout (Oncorhynchus mykiss), brown trout (Salmo trutta), and other non-native fishes from the Colorado River from above and below the confluence of the LCR and the Colorado River. The purpose of the translocation is to 35