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I I I I I I I I I I I I I I I I I I I An analysis of average lengths and CPE in the fall and following summer for the 1985, 1986 and 1987 year classes is presented in Table 22. YOY captured in the fall (September only) of 1985 (n=295) averaged 15.7mm longer than those captured in the fall of 1986 (n=297). By the following spring of the respective years, the size difference was only 7.2mm (n=32 for 1985; n=60 for 1986). Although fall CPE for the two year classes (2.0 for 1985 and 6.0 for 1986) differed considerably, CPE in the following July was nearly equal (0.23 and 0.29). These data indicate that other factors are involved in year class success of Colorado squawfish besides spawning time. Winter and spring river temperatures as well as the extent of icing probably has a profound effect on survival and growth of these fish. Although sample size may be sufficient, these data suggest that monitoring YOY in the fall may not be a good index to year class strength. Humpback Chub A total of 21 humpback chub were captured during this study in 1987. This included 6 adults, 11 juveniles (Table 23), 4 YOY, and 0 larvae (Table 24). In 1985 and 1986, 11 and 17 humpback chub, respectively, were captured in Cataract Canyon using similar sample methods (Valdez 1985, 1987). These findings and those of past studies (Valdez et al. 1982), indicate that either the population of humpback chub in Cataract Canyon is small and dispersed, or the turbulent conditions preclude thorough sampling to locate concentrations of the species. Furthermore, the taxonomic dilemma with the Gila complex prevails in Cataract Canyon, and is it often difficult to classify a fish from the area with confidence. In order to address this problem and therefore, the second objective of this investigation (i.e. Determine whether humpback chub popula- tions exist in Cataract Canyon), a 'Chub Biography' is being submitted as a supplement-to this Annual Summary Report. This biography contains a collection of photographs and descriptions of the Gila complex captured in Cataract Canyon, primarily in 1987. Copies of this biography are also being sent to select investigators with expertise in chub taxonomy. These investigators are being asked to render an opinion on the tentative identifications presented, and such opinion may result in reclassification of some of these forms. We believe that a population of humpback chubs exists in Cataract Canyon, but we hypothesis that it consists of a form unique to the region, perhaps a geomorph. The chubs classified as G. cypha in Cataract are generally smaller (most are less than 200 mm TL), have a blunt head, a shallow nuchal hump, an overhung snout, scaleless nape and breast, and a relatively deep body. However, the dorsal and anal fin ray counts are not consistently 9 and 10, respectively, as is typical of the species; and the extreme morphological features such as a pronounced hump are absent. Closer examination of these chubs is needed to determine if they represent the genotype for G. cypha, even though they differ phenotypically. Adults. Six adult humpback chub were handled in 1987 (Table 23). The more robust ones were equipped with a serially-numbered red Carlin tag and released. Although none of these fish exceeded the acceptable minimum length of adults, these fish were nevertheless classified as adults because collection of larvae 22