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<br />reduced to a level that would improve survival and recruitment of native fishes, to <br />identify the level of effort required, and to determine movement patterns of small mouth <br />bass. Based on knowledge gained during the preceding years we refined our tasks <br />(Scope of Work objectives) each year resulting in the following: <br />1. Obtain an estimate of the number of smallmouth bass in the 24-mile <br />treatment reach in Little Yampa Canyon and a 5-mile reach in Lily Park <br />using a mark-recapture abundance estimator. <br />2. Remove a large portion of the estimated population of small mouth bass <br />from the 24-mile treatment reach in Little Yampa Canyon and the 5-mile <br />concentration area in Lily Park. <br />3. Calculate the proportion of smallmouth bass removed from each study <br />area based on initial population size. <br />4. Remove large numbers of age-O and age-1 smallmouth bass from the 12- <br />mile treatment reach in Little Yampa Canyon (This is the lower section of <br />the 24-mile study reach and corresponds with the treatment reach for the <br />Native Fish Evaluation Study # 140). <br />5. Understand movement of recaptured smallmouth bass. <br /> <br />Historical background of smallmouth bass invasion in the Yampa River-Smallmouth <br />bass were first introduced to the Yampa River basin in 1978 when the Colorado <br />Division of Wildlife stocked the species in Elkhead Reservoir. This 450-acre mainstem <br />reservoir was built in 1974,5 miles upstream from the Yampa River confluence on <br />Elkhead Creek, a Yampa River tributary located 148 miles upstream from the Green <br />River confluence. Prior to reservoir stocking, smallmouth bass did not occur in the <br />Yampa River based on their absence from fish collections in 1951, 1967-1971, and <br />1976-1977 (Bailey and Alberti 1952; Holden and Stalnaker 1975; Carlson et al. 1979). <br />Although both the spillway and the outlet structure at Elkhead Reservoir were <br />unscreened, fish escapement was not initially considered a problem by resource <br />managers because small mouth bass were very rare in the Yampa River for several <br />years after stocking. For example during extensive boat electrofishing in 1981 and <br /> <br />2 <br />