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<br />8 <br /> <br />Job 5: <br /> <br />Flow regime effects on reproductive success of native and non- <br />native fishes in the Yampa and Colorado rivers. <br /> <br />Sampling for young-of-the-year and juvenile fishes in the Yampa River was <br />conducted annually from 1980-1984 by the Colorado Division of Wildlife from <br />Cross Mountain Canyon (RK 90) to the Green River confluence. The database <br />resulting from these collections was computerized in 1985. Organization of <br />this database by species and gear type was necessary to identify the young- <br />of-the-year (YOY) size group for each species, and partition the database for <br />only seine-collected YOY. From these data, catch/effort (c/f) and frequency <br />of occurrence indices for each of eight species (4 native, 4 non-native) were <br />calculated by year and by river stratum each year. Two spawning period <br />indices, number of days to first spawn and total number of days, were also <br />estimated each year for each species. These indices were related to flow and <br />temperature indices including spring maximum discharge, mean and total monthly <br />estimates of discharge for May through July, and 16C, l8C, and 20C degree days <br />for May through July. <br /> <br />Characterization of flow years <br /> <br />Spring flow regimes occurring during 1980-1984 have been described as some <br />of the highest and lowest on record. In order to better describe and compare <br />these flow years, peak flow and total May-June-July discharge were determined <br />from USGS Maybell-Little Snake or Deerlodge gage records for each year. <br />Collection of flow data at Deerlodge, located at the head of Yampa Canyon, was <br />initiated in 1982. Yampa River flow indices for 1980 and 1981 required <br />adjustment of Maybel1 gage records to account for inflow from the Little Snake <br />River (see Figure 1). Flow data for each month in 1980 and 1981 at Maybe11 <br />was summed with corresponding Little Snake River flow data at Lily Park in <br />order to approximate flows for the Yampa River at Deer10dge immediately <br />downstream. Peak flows for 1980-1984 were also compared to the historical <br />record from 1934-1989 using Maybe11 gage records. The 56-year record of peak <br />flows were ranked and the sample years were put in historical perspective with <br />a numerical and percentile rank. <br /> <br />Correlation analyses <br /> <br />Simple correlation coefficients were used to relate species abundance <br />indices with flow and temperature indices. Due to the survey sampling nature <br />of the existing data base, the less rigorous statistical treatment was deemed <br />most appropriate. The objective was to determine if a statistically confirmed <br />relationship between these indices existed, not establish cause and effect. <br />Biological indices derived from seine sampling included annual estimates of <br />number of fish caught per unit effort (CPUE) and frequency of occurrence (FO) <br />of a particular species in the samples for each reach and for all reaches <br />combined from 1980-1984. It was presumed that CPUE and FO for each species <br />may be highly correlated, but FO was included as a separate index of <br />comparison because it also may describe distribution related to flows versus <br />YOY abundance. Other biological parameters derived from sample dates and <br />species YOY sampled were number of days to first spawning (SPAWNl) and number <br />of days in the spawning season (SPAWNT). SPAWNl was estimated using April 1 <br />