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and reach reproductive maturity by next spring. During the monitoring trip, a humpback chub was observed attacking speckled dace. Perhaps, a dietary shift to piscivory may have increased the growth rate in some individuals since fish have a higher caloric value (Cummins and Wuycheck 1971; Stahl and Stein 1994), greater assimilation efficiency (Brett and Groves 1979), and larger food volume per capture compared to most invertebrates. Alternatively, the unmarked individuals may have actively migrated into this area. The fact that 78% of untagged individuals were captured in the five lowest nets, which is above but closer to the Chute Falls "barrier" than other nets, would suggest that they were recent upriver migrants. If humpback chub consistently inhabit this area, then it is likely that some individuals should have been detected during previous studies (e.g., Kaeding and Zimmerman 1983; Mattes 1993; Strength 1997). Also, the 60 baited net sets deployed during the July 2003 reconnaissance trip constituted a relatively intensive sampling effort (i.e., 1,345 hours), yet no humpback chub were captured. This would suggest that if unmarked individuals were new migrants, then they likely swam above Chute Falls during the intervening 3 months when the LCR was typically flooding. However, it is also feasible that humpback chub have always eluded detection in the past and a small population was already present. If future monitoring efforts capture a previously PIT tagged humpback chub that migrated above Chute Falls from the lower corridor, then perhaps this issue can be resolved. Our findings from this translocation experiment are both enlightening and intriguing. Additional data will be gathered during the ensuing 2003 spring "post-winter-flow" and fall "post-monsoon" monitoring trips, which hopefully will resolve some unknowns and improve our understanding of humpback chub life history. We will also conduct a second translocation trip in late summer 2004. By then, we hope to find a more permanent nonlethal mark (e.g., different elastomer color, PIT tags, batch marks) so less future uncertainty arises when capturing humpback chub above Chute Falls. COOPERATORS U.S. Bureau of Reclamation and U.S. Geological Survey (Grand Canyon Monitoring and Research Center) provided funding; U.S. National Park Service (Grand Canyon National Park) and Navajo Nation concurred with the experiment and supplied relevant permits; and Arizona Game and Fish Department has and may continue to supply personnel for the project on various trips. ACKNOWLEDGMENTS We wish to thank Dewey Wesley, Shaula Hedwall, and Kara Hilwig (U.S. Fish and Wildlife Service), David Ward and Joey Slaughter (AZ Game and Fish Department) for their field assistance; Tom Gushue and Carol Fritzinger (U.S. Geological Survey) for creating maps 17