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r STATUS OF GREEN RIVER COLORADO PIKEMINNOW 1357 (95% confIdence interval, 2.900--3,707) but declined to 2,142 fish (1,686-2,598) by 2003, a 35% reduction. However, accounting for a reach not sampled in 2000 makes it likely that the reduction was 48% over the 2000--2003 period. The abundance of recruits (400-449 mm) in the study area averaged 8.9% of adult abundance. The annual survival rate for 2000--2003 was 0.65 (0.59-0.71), lower than the 0.82 rate estimated for 1991-1999; mortality exceeded recruitment. The few captures and lack of recaptures of fish of at least 800 mm suggest that apparent survival was low for large Colorado pikeminnow. The reduced abundance of adult Colorado pikeminnow was due, in part, to the weak year-classes of age-O fish produced in the 1990s and the reduced survival of recruits and adults in 2000--2003, Based on these results, downlisting of this species is not warranted at this time. Better understanding of the factors that influence adult survival rates, abundance dynamics, and the recruitment of early life stages as well as the effects of flow recommendations and nonnative predaceous fishes would assist the conservation of Colorado pikeminnow. Demographic parameters that describe birth, move- ment, and mortality rates and population abundance are useful for understanding the status and dynamics of animal populations. The responses of populations to biotic and abiotic drivers are of interest to ecologists attempting to understand the fundamental basis for population change. They are also useful to managers attempting to maintain or enhance the abundance of free-ranging animal populations. The Colorado pikeminnow Ptychocheilus lucius is a large, predaceous, and migratory cyprinid endemic to the Colorado River basin that is listed as endangered under the Endangered Species Act of 1973, as amended (U.S. Fish and Wildlife Service 1974). Once wide- spread and abundant throughout warmwater reaches of the basin, wild Colorado pikeminnow are presently restricted to the San Juan, Colorado, and Green River subbasins of the upper Colorado River basin. Reasons for the decline of Colorado pikeminnow include habitat alteration, river regulation, and the presence of nonnative fishes (Minckley 1973; Carlson and Muth 1989; Tyus 1991). Over 140 main-stem and tributary dams and reservoirs and several transbasin water diversions provide water for agricultural and municipal purposes to a rapidly expanding human population in the Colorado River basin. As a result, the Colorado River basin is one of the most tightly controlled water supplies in the world (Ioms et al. 1965; Carlson and Muth 1989). Main-stem dams have been particularly damaging to biota because they restrict the movements of mobile fishes such as Colorado pikeminnow, reduce the seasonal variability of discharge, water tempera- ture, and sediment load, and increase daily hydrograph variation (Vanicek and Kramer 1969; Holden 1979; Ward and Stanford 1979; Stanford et al. 1996; Poff et al. 1997). No fewer than 60 nonnative fishes have been established in the Colorado River basin, many of which prey on or compete with various life stages of native species (Carlson and Muth 1989; Ruppert et al. 1993; Bestgen et al. 2006a; Olden et al. 2006). The outcome of these environmental and biotic changes for the highly endemic fish fauna of the Colorado River basin has been dramatic: 2 of the 35 native species in the basin are extinct, an additional 18 (including the Colorado pikeminnow) are federally listed as threat- ened or endangered or are very rare, and most others are listed by one or more states in the basin as declining (Stanford and Ward 1986; Carlson and Muth 1989; Bezzerides and Bestgen 2002; Mueller and Marsh 2002; Valdez and Muth 2005). Recovery of Colorado pikeminnow will require a genetically and demographically viable, self- sustaining population in the Green River subbasin; and self-sustaining populations that meet or exceed estimated carrying capacity either in the upper Colorado River subbasin or in both the upper Colorado River subbasin and San Juan River subbasin. [U.S, Fish and Wildlife Service 2002.] For the Colorado pikeminnow to be downlisted to threatened status or delisted completely, three demo- graphic criteria would have to be met in the Green River subbasin over the specified monitoring period: (1) the abundance estimates for adults (total length [TL] , 2:450 mm) in both the middle and lower Green River are not declining significantly, (2) the estimated mean recruitment of fish 400-449 mm TL (e.g., recruits) equals or exceeds the estimated mean annual adult mortality for the subbasin, and (3) each abundance estimate for the subbasin exceeds 2,600 adults (U.S. Fish and Wildlife Service 2002). We report population abundance, survival, and recruitment rates and population trends for Colorado pikeminnow in the spatially extensive Green River subbasin based on intensive capture-recapture data collected from 2000 to 2003 and additional interagency monitoring data collected since 1991 and interpret those data in light of present recovery goals for this species. Status and Natural History of Colorado Pikeminnow The abundance of Colorado pikeminnow varies by more than an order of magnitude in the three occupied subbasins of the upper Colorado River basin. The wild population in the San Juan River subbasin, which is separated from the remainder of the upper Colorado River basin by Lake Powell Reservoir, is relatively