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I I I I I I I I I I I I I I I I I I I 23% were over 55 cm at Duffy (Figures A2. 5a, 52, 53, and 54). In contrast catfish under 30 cm were common on the Colorado River (Figure A2.55) and only 5% were over 55 cm. Length frequency histograms for other species are included in Appendix C. White sucker and small mouth bass were the only species in the Yampa River with a large percent ofYOY or yearling sized fIsh in the main channel. YOY bass were abundant at Duffy but rare at the Sevens in both years (Figures A2.59, 60, 61, and 62). By September 1999 the mean length ofYOY small mouth bass at Duffy was 65 mm which was higher than what was identified for fish from 1998 (60 mm) (Table 5). In Table 5, the fish from August 12 and 17, 1999 were collected by seining and the fish from later dates by boat electrofishing. Table 5: Mean length with sample size ofYOY small mouth bass for each sample date at Duffi in 1998 and 1999. 1998 sample 3-Sep 15-Sep 22-Sep 30-Sep 16-Sep 24-Sep MM 60 64 70 70 Sample size 47 60 228 31 1999 sample 12-Aug 17-Aug 24-Aug 31-Aug 15-Sep 25-Aug 2-Sep 17-Sep MM 38 47 53 65 66 Sample size 33 15 91 23 35 DENSITY ESTIMATION Fish density estimates were similar between years on the Yampa River at both sites. The 1998 total fish density for the long Sevens reach was estimated to be 950/1an"= 78 (95% C.L) not significantly different than the 1999 estimate of I I 37/km "= 182. This was in spite of the fact the sampling station was reduced in size by about half in 1999. The total fIsh estimate for the long Duffy station (Representative Reach) in 1998 was 41J/km "= 40 which was not significantly different from the 1999 estimate of 409/km "= 29. The fish sampling site was about the same total length in both years, but shifted upstream by about 0.75 Ian. 35