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between study periods 1994 to 1996 and 2002 to 2004. We present data for native fishes and <br />selected, potentially problematic, non-native species. <br />Native fishes.-Mountain whitefish was found throughout the study area but was most <br />common in upstream Browns Park, was moderately abundant in Lodore Canyon reaches, and <br />was comparatively uncommon in Whirlpool Canyon and Island-Rainbow Park. Relative <br />abundance and CPUE of mountain whitefish in Lodore Canyon electrofishing samples in the <br />2002 to 2004 period were dramatically lower than in the 1994 to 1996 period (Fig. 12). <br />Mountain whitefish now comprises 2% or less of the fish community in all reaches and analysis <br />of CPUE data indicated a significant decline (Table 8). Abundance of mountain whitefish in <br />seine samples was greater in nearly all reaches in the recent period than in 1994 to 1996, and <br />particularly so in Browns Park and LD3 reaches (Fig. 12). This may be due to collection of <br />more seine samples in spring when young mountain whitefish were more abundant. Relative <br />abundance and CPUE data for mountain whitefish and other species generally tracked each other <br />reasonably closely. This suggested that each metric was a surrogate for the other and that <br />changes in relative abundance between the 1994 to 1996 and 2002 to 2004 periods may reflect <br />actual changes in density. The abundance of small mountain whitefish in Browns Park seine <br />samples and their low abundance elsewhere suggested that most fish in downstream reaches <br />were derived from upstream. <br />Size-structure of mountain whitefish from electrofishing data showed that the majority of <br />fish captured were in the 101 to 200-mm TL size class in each of the 1994 to 1996 and 2002 to <br />2004 periods (Fig. 13). More large fish were found in the 2002 to 2004 period than earlier, <br />especially in the upper portion of Lodore Canyon. We captured only small mountain whitefish <br />in Island-Rainbow Park. Most of those were captured in spring, with few or none in summer or <br />autumn. Based on size of fish captured in seine samples and downstream absence of adults, <br />autumn-spawning mountain whitefish hatched prior to spring runoff and may be dispersed <br />downstream by higher spring flows. <br />Adult Colorado pikeminnow were found in all Lodore Canyon reaches in both time <br />periods and Whirlpool Canyon and Island-Rainbow Park in 2002 to 2004. Relative abundance <br />27