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I I I I I I I I I I , I I I I I I r I to be frequently dragged in shallow reaches. Dragging became the case for the Hyside at flows less than 100 cis on the Yampa. The boat was maneuvered by either oars or by a battery powered 40-pound thrust trolling motor. Two nellers caught as many fish as they could while the shocker was in operation. All fish were measured to the nearest millimeter. Only fish over 150 mm were marked and therefore used for mark and recapture population estimates. Density estimates were made for the each study site on the Yampa, Colorado and Dolores. The Darroch multiple mark method (Everhart and Youngs] 981) was used to make the population estimate with ninety-five percent confidence intervals. A total fish eslimate was made for all species and for each species. Recapture rates generally varied between species and size-groups. For our samplings larger suckers had the highest recapture probabilities. Species with appreciably lower recapture probabilities included catfish, bass, pike and carp (the lower group). The total fish estimate was a blend of recapture probabilities, but should produce reliable comparisons for total fish abundance between years, when species and size composition was consistent. For rare species (pikeminnow, etc) with zero or one recapture in the sample, abundance was estimated by dividing the number in the sample by the mean recapture probability of the lower group. The z-test with an alpha of 0.05 (z = 1.96) was used to test for significant differences in density estimates between years at each station. At stations with three or more years of sampling, the Bonferroni inequality was also used to control the overall significance level (.05) for the simultaneous comparison of all pairs of years (Dr. David Bowden, CSU. pers. communication). At stations with 4 years of data, (Duffy and Sevens) the z value (2.631) corresponds to an alpha of 0.05 divided by six (0.0083). On the Yampa River, a different mark was used for each run-riffle sequence, which allowed for determining ifrecaptured fish had moved up, down or had not moved between captures. The dates and the flow for each field trip during the four-year period 1998 to 200 I for Sevens and Duffy are given in Table 3. The Lily Park Site was electro- fished for two years in 2000 and 2001 (Table 3). Flow readings were taken from the Maybell gage. Flows recorded from the Lily Park gage tended to be somewhat higher than Maybell and are included in Table 3 parenthetically. On the Colorado River, fish in both study sites within the IS-Mile reach were marked to designate the upper, middle and lower sections of the site to give a general idea of movement between passes within the station. A total of eight electro-fishing passes were made at the Com Lake station in 1999. Four passes were made on the left half and four on right half of the river. The Clifton site was added in 2000 and fish from Clifton were given a unique mark so they could be distinguished from fish marked downstream at the Corn Lake station. The sampling strategy was modified in 2000. The total number of electro-fishing passes was six at both Com Lake and Clifton. Instead of sampling left and right sides, the river was divided into three longitudinal zones, i.e., right shoreline, left shoreline and mid channel so that fish caught in shallow shoreline habitat were distinguished from the deeper channel habitat. The electro-fishing boat sampled each zone (right and left shoreline and mid channel) twice. In 200], the same 13