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<br />c) <br />c:) <br />...... <br />CD <br /> <br />c..~ <br /> <br />Juan River were generally shallower than those in the Colorado River but similar to those in the Green <br />River. San Juan River backwaters were similar to the other two rivers in water quality (temperature, <br />dissolved oxygen) and productivity features (phytoplankton, periphyton, zooplankton, benthic <br />invertebrates), indicating that overall productivity appeared to be similar to other areas considered good <br />Colorado pikeminnow nursery areas. Bliesner and Lamarra (2000) found that backwater depth and <br />productivity were reduced by storm events when fine sediments were deposited in backwaters. Archer <br />(2000) compared invertebrate numbers from San Juan River Reach I and Reach 4 nursery habitats <br />(backwaters) with a Colorado pikeminnow nursery area in the Green River near Ouray, Utah, during <br />August and September ofl995 and 1996. He found that invertebrate numbers in Reach I were lower than <br />in either Reach 4 or the Green River, and that numbers in the San Juan River declined from August to <br />September, whereas in the Green River they did not decline. Archer (2000) concluded that late summer <br />thunderstorm activity in the San Juan River decreased invertebrate numbers in nursery habitats, indicating <br />food limitation may have occurred at this time. Retention and growth of stocked Colorado pikeminnow <br />in the San Juan River in both 1996 and 1997 were high (Trammel and Archer 2000), suggesting that for <br />the number of fish that were retained in the river, food did not appear to be a limitation. Archer (2000) also <br />measured lipid content ofYOY Colorado pikeminnow stocked in Augustl997. Lipid content was initially <br />high in the hatchery-reared fish, declined in September and October shortly after stoclcing, and rose in <br />December. Archer (2000) noted that the decline in lipid content after stoclcing was normal for stocked fish. <br />The increase in lipid content by December, along with good growth of the stocked fish, shows that food <br />was not limiting to them, even though flooding events occurred in September 1997. Infonnation from these <br />various studies clearly shows that food availability declines in the San Juan River in the fall as a result of <br />thunderstorm flood events, but no evidence of food limitation could be seen in the stocked Colorado <br />pikeminnow. <br /> <br />Bliesner and Lamarra (2000) also evaluated general habitat quality and productivity in the San Juan River <br />and compared it with similar studies in the Colorado River. This study looked at runs and riffles, the two <br />most-common habitat types. The results showed that the San Juan River was very similar in overall habitat <br />quality to the Colorado River. <br /> <br />Habitat quality in San Juan River key habitats is comparable with similar habitats in the Green, Yampa, and <br />Colorado rivers. This suggests that overall habitat quality in the San Juan River is not limiting. But the <br />frequency of late summer storm events in the San Juan River has the potential to reduce habitat quality by <br />depositing fine sediments, which could possibly cause habitat limitations for the native fishes. <br /> <br />Habitat Summary <br />During the 7-year research period, many key habitats for Colorado pikeminnow and razorback <br />sucker were identified. Key habitats for adult Colorado pikeminnow in the San Juan River <br />include relatively low-velocity eddies, pools, and slackwaters, along with the riffle/runs and chutes used <br />for spawning. More-common run habitat is used, but the other lower-velocity habitats are selected <br />during most seasons, suggesting they are more important to the fishes. Wanner habitats, typically <br />low-velocity habitats, appear important during the pre-spawning period. In addition, these habitats <br /> <br />September 2000 <br /> <br />3-33 <br /> <br />Program Evaluation Report <br />