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9. Status of native fishes in the Grand Canyon, 2005 Authors: L.G. COGGINS, S. ROGERS, C. NELSON, W. PERSONS, D. GWINN, W. VERNIEU, S. HUEFTLE, M. YARD, M.E. ANDERSEN, USGS, Southwest Biological Science Center, Grand Canyon Monitoring and Research Center, Flagstaff, AZ Abstract: The level of Lake Powell has been dropping over the past few years due to upper basin drought conditions. This resulted in increased Glen Canyon Dam release temperatures and resuspension of sediments with high oxygen demand, resulting in lower release oxygen concentrations. While the reduced oxygen concentrations were corrected by modified dam operations, temperatures remained high. Natural resource managers in the Grand Canyon have been monitoring and managing native and nonnative fishes in the Colorado River below Glen Canyon Dam during the time when these changes have been occurring. Numbers of native fishes in the Colorado River and Little Colorado River in the Grand Canyon appear to have stabilized or increased in 2005. The Age Structured Mark Recapture model results suggest that the humpback chub population appears to have stabilized, albeit at low levels compared to the historic population size. Numbers of other native fishes, including flannelmouth sucker, bluehead sucker, and speckled dace all appear to be increasing as compared with prior years. The proportion of native fish making up the entire sampled fish community is increasing relative to nonnative fishes. While the reasons for these changes are not certain, it appears that warmer river water temperatures and mechanical removal of nonnative salmonids may be influencing these results. Native fish managers in the Grand Canyon are concerned that warming water temperatures may increase the frequency and numbers of nonnative warm water fish and parasite species. A warm water nonnatives workshop was convened in December. Expert advice was solicited to help address this management challenge in the Grand Canyon. 10. Humpback and Roundtail Chub Population Estimates in Westwater Canyon Author: JULIE JACKSON, Utah Division of Wildlife Resources Abstract: One of the most robust populations of the federally endangered humpback chub (Gila cypha) is located in Westwater Canyon on the Colorado River. This population has been monitored annually since 1988 through trends in catch rates. Revisions to recovery goals in 2002 for humpback chub required that mark-recapture population estimates be completed in three of every five years. The first cycle of population estimates for humpback chub in Westwater Canyon was conducted from 1998 to 2000. Results from 1998 to 2000 indicated a declining but statistically non-significant trend. The second cycle of population estimate sampling for Westwater humpback chub was conducted from 2003 to 2005. Estimates for these three years showed a persistent downward trend. The 2005 estimate was considerably lower than the 1998 estimate and indicated a significant decline. Analysis of catch per unit effort (CPUE) data from this project and historic interagency standardized monitoring (ISMP) indicated an ongoing declining trend in mean CPUE for humpback chub that was significant. In addition to the humpback chub population estimates, roundtail chub (Gila robusta) populations 11