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9 <br /> <br />RESULTS AND DISCUSSION <br />General <br />I. Sampling Bias/Selectivity <br />Several sources of sampling bias are inherent in the design of this study <br />and should be acknowledged. <br />A. Gear Selectivity. Built-in bias against the capture of adults <br />of larger species is inherent in the use of relatively short <br />(3.0 and 1.0 m) seins of small mesh (0.79 and 1.6 mm). However, <br />gear selection is consistent with the objective of sampling <br />young-of-the-year (YOY) fishes. <br />B. Habitat Selectivity. Design and size of sampling gear is biased <br />against the sampling of deeper swifter sites. Such sites could <br />be more efficiently sampled with electrofishing and/or passive <br />netting techniques; however, these methods would not capture <br />YOY forms and most juveniles. <br />C. Seining Efficiency. Efficiency varies according to both width <br />and depth of the individual sein haul and substrate. This study <br />is not designed to account for sein efficiency variability. <br />II. Yampa River Study Area. <br />A total of 422 samples were collected during March - August, 1981 (Table 1). <br />Laboratory processing and computer storage of these data has been <br />completed, as well as a preliminary data analysis. A total of 103 samples <br />have been collected during April - June, 1982; however, these samples <br />will be processed during fall-winter, 1982. A total of 18 species have <br />been identified from 1981 samples, of which seven were native (Table 2). <br />Unidentified YOY chubs (Gila spp.) await taxonomic clarification and are <br />listed here as a single taxon. Several specimens of immature minnows <br />and suckers could not be positively identified due to their early stage <br />of development and are listed as "unidentified Cyprinidae" and "unidentified <br />Catastomidae", respectively. <br />For the Yampa River study area as a whole, 19,058 fishes were identified <br />in 1981. Of these, the introduced red shiner (Notropis lutrensis) <br />was the predominant species (7563 individuals) and native unidentified <br />chubs (Gila spp.) were the second most numerous (5823). The number of <br />individuals of native species was slightly smaller (9398) than introduced <br />species (9660). Based on a length-frequency analysis for YOY Yampa <br />fishes (Appendix C), 1981 spawning periods for the eight most abundant <br />species were determined (Figure 2). Species-habitat associations have <br />not been completed and these will hopefully be conducted utilizing the <br />MANAGE program. <br />III. Colorado River Study Area <br />A total of 354 samples were collected during April - July, 1981 (Table 3). <br />Sample number per habitat type has not been compiled, nor has computer <br />