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6 . Executive Summary Estimated annual survival of adult humpback chub was 0.755, but the 95% confidence intervals place this estimate as high as 0.896. Sub adults in the mainstem, up to 3 years of age, had an estimated annual survival of about 0.100, and over 3 years only 1 in 1,000 fish survive to recruit as adults. Although the various sources of mortality were not quantified, marking studies indicate that movement to reaches downstream of the LCRI aggregation probably resulted in a permanent loss of individuals to the aggregation. Low estimated numbers of subadults surviving to adult in the mainstem suggest that recruitment may not be sufficient to offset mortality of adults. A smaller than expected number of younger adults (based on length- frequencies of adults captured) indicates that most of the recruitment of mainstem adults may be from the LCR and not from survival of younger chubs in the mainstem, It was estimated that brown trout, rainbow trout, and channel catfish potentially consume about 250,000 subadult humpback chub annually in the 26.4-kin subreach between the LCR and Bright Angel Creek. Surviving fish that are transported into the Inner Gorge probably have low survival because of limited shoreline habitat and high predator densities. Young humpback chub that descended downstream of Lava Rapid (RM 65.4) did not ascend this point to return to the LCRI aggregation, and hence, recruitment potential was lost from the LCR population. MOVEMENT Adult humpback chub in Grand Canyon exhibited strong spatial fidelity for specific river sites, similar to behavior observed in other populations, Average net displacement (distance from first to last radio contact or capture site) for radio-tagged and PIT- tagged adults in Grand Canyon was only 1.49 kin and 0.99 kIn, respectively, which was similar to 0,8 kin and 1.67 kIn, respectively for adults in the Black Rocks reach of the Upper Colorado River Basin (Valdez and Clemmer 1982). Average time of radio contact for radio-tagged fish and between captures of PIT -tagged fish was 93 days and 406 days respectively. Adults in Grand Canyon however, demonstrated greater gross displacement (sum of distances between radio contact sites) of 5.13 kin compared to 1.64 kin in Black Rocks, primarily as a result of spawning migrations from various Final Report mainstem locations into the LCR Maximum round- trip distance traveled by an adult from the mainstem into the LCR for spawning was 40 kIn, although the only mainstem adults that migrated to the LCR were from within a 13.5-km subreach (RM 57 - RM 65.4). The majority of these fish returned to locations within 2 km of their premigration sites (Fig. 6). The home range of the adult portion of the LCR Inflow (LCRI) aggregation was 28.4 kIn, including 13.5 kin in the mainstem and 14,9 km in the LCR Adults moved very little between aggregations, indicating that most adults throughout the canyon were associated with groups of fish at specific river locales, Of 1,524 adults captured in the LCRI aggregation (280 recaptured), only two were recaptured outside of the 13.5-km mainstem area in other downstream aggregations. Also, four sub adults (>175 nun TL) were recaptured downstream of the LCRI aggregation in the adjacent aggregation, Long-range movement and local activity of adults in the LCRI aggregation were greatest during spawning-related behavior from February through May. Adults moved to large local congregations in disjunct eddy complexes in February, then migrated to stage at the LCR inflow, prior to ascent into the LCR for spawning. Adults from upstream and downstream of the LCR moved simultaneously to the LCR inflow, suggesting that external reproductive stimuli, such as photoperiod, cued gonadal maturation and pre-spawning migrations. Remote radiotelemetry indicated an average residence time of about 17 days at the LCR inflow by staging adults, suggesting that the fish accumulated temperature degree days for gonadal maturation. This pre-spawning staging led to significantly higher catch rates of adults in this area in late January - March (Fig, 7). Adults ascended the LCR during decreasing LCR flows, increasing water temperatures, and decreasing turbidity, indicating that spawning ascent was cued by conditions in the LCR, while mainstem staging was cued by other factors such as photoperiod and slight seasonal mainstem wanning. Adults in the mainstem moved very little during non-spawning periods, in summer, fall, and winter (July-January), when local movement was primarily influenced by time of day, turbidity, flow magnitude,