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Wallis). The distribution of catch rates around the mean was significantly different among years (p < 0.05; Kolmogorov-Smirnov). Length-frequency analysis of roundtail chub (>_ 150 mm) data collected via ISMP protocol from 1988-2000 indicates frequent shifts in size structure (Figure 12). Roundtail chub in Westwater Canyon appear to predominantly move between single mode and bimodal size distributions. DISCUSSION Population Estimates t Population estimates of humpback chub in Westwater Canyon demonstrated a downward trend from 1998 to 2000. This trend is consistent with the point estimates (1998-2000) of humpback chub in Black Rocks (McAda 2003). Previous population estimates (Chart and Lentsch 1999; Nesler 2000), while not as robust, indicate that the humpback chub population in Westwater Canyon is highly variable. Chart and Lentsch (1999) determined the population to be 5,621 individuals in 1994, . 10,148 individuals in 1995, and 5,186 individuals in 1996. Nesler determined the Westwater Canyon humpback chub population to be anywhere from 5,719 in 1993 (90% survival) to 1,164 in 1997 (59% survival). Point estimates in Westwater Canyon for 1999 and 2000 maybe indicative of a leveling off prior to a rebound in the humpback chub population, or the declining trend could continue. The Westwater Canyon roundtail chub population appeared to be relatively stable from 1998 to 2000. Chart and Lentsch (1999) indicated that the roundtail chub population was declining ~ in the period from 1993 to 1996 (6,809 in 1993, 5,733 in 1994, and 2,551 in 1996). These combined datasets further support the observed variability of chub populations in Westwater Canyon. Identical effort-was applied toward the capture of humpback chub and roundtail chub throughout the three years of the study, and, therefore, increases the likelihood that the humpback chub decline is real and not an artifact of sampling bias. This study was not designed to sample for subadult humpback chub in Westwater Canyon for the purpose of generating subadult abundance estimates. Future efforts should include a component of sampling designed to capture subadult humpback chub. This would provide information toward the recovery goal component of determining mean estimated recruitment of humpback chub and also ~ provide additional insight toward population dynamics of the Westwater Canyon population as revealed by the adult population point estimates. Humpback chub and roundtail chub population size patterns observed in this study and by Chart and Lentsch (1999) may indicate that these two species coexist in Westwater Canyon through an ~ equilibrium of population dynamics. While these two studies are not strictly comparable due to different approaches to sampling and analysis of the data, some general observations can be made. From 1993 to 1996, the Westwater Canyon roundtail chub population appeared to be declining. At the same time, the humpback chub population was variable, but relatively higher. Conversely, from 1998 to 2000, adult humpback chub appeared to decline and stabilize while the roundtail chub population was stable and relatively higher. Population estimates of Westwater Canyon humpback ~ chub scheduled for 2003-2005 will contribute to the existing data and further clarify the short-term ~ 9