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The penstock modification was completed ahead of schedule and, <br />consequently, the growth study was not funded until after the penstock <br />modification became operational. Furthermore, adequate electrofishing <br />gear was not available until 1981 and sampling schedules were frequently <br />interrupted. Premodification growth data were, therefore, not <br />systematically collected; however, data from electrofishing samples <br />collected in 1977 included measurements of marked trout stocked as <br />fingerlings in 1976. In addition, back calculated growth of creeled fish <br />had been estimated between 1964 and 1970. The data from the 1964-1970 <br />period was available only in summarized form, but records of individual <br />measurements from 1977 were obtained and differences between growth <br />increments measured in 1977 and the present study were summarized and <br />tested. Growth differences were tested primarily using the general linear <br />models procedure for analysis of variance for unbalanced data, employing <br />the Statistical Analysis System (SAS) of packaged computer programs. <br />Continuous temperature records were obtained during 1979, 1980, and <br />1981 at Tailrace, Little Hole, and Browns Park (at mile 22, see Figure 1) <br />using Ryan thermographs. Temperature records for the period prior to <br />penstock modification were obtained using thermographs and from continuous <br />penstock water temperature records maintained by the Bureau of Reclamation. <br />RESULTS - OBJECTIVE #1 <br />Mean annual growth for the 1976 year class of rainbow trout, as <br />measured at Tailrace in 1977, was 64.2 mm. During 1979, the first full <br />growing season the penstock modification was operational, mean annual <br />growth at Tailrace increased to 183.3 ± 14.4 mm, a highly significant <br />improvement (p = 0.01). Growth for all samples taken from Tailrace and <br />-17-