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ISMP backwater sampling evaluation <br />of electrofishing. The 50 ISMP seine hauls completed in the 25 backwater samples encompassed <br />an average of 22 % (5 to 94 %) of the surface area of each backwater. <br />Sampling detected a total of five native and 13 introduced fishes and samples contained a <br />total of 70,642 fish (Appendix II). Native fishes comprised 2.0 % of the total catch (Figure 5); <br />the most abundant native species was speckled dace Rhinichthys osculus (0.7 %; n = 560). One <br />Colorado pikeminnow (approx 35 mm TL) was captured and released in the Colorado River in <br />1998 in a sub-reach 3 backwater approximately eight kilometers downstream of the confluence <br />with the Gunnison River. <br />Non-native species represented 97.9 % of all fishes captured and sand shiners (41 %), red <br />shiners (26 %) and fathead minnows (21 %) were again the most abundant taxa. Centrarchids <br />were 5.1 % of the total number of fish captured; those were mainly green sunfish (3.0 %) and <br />largemouth bass (1.9 %). In all, 2,176 green sunfish (16 to 174 mm TL) and 1,366 largemouth <br />bass (45 to 245 mm TL) were removed from the 24 backwaters sampled in the Grand Valley <br />reach of the Colorado River in autumn 1998. Most largemouth bass captured in backwater <br />samples in both years were relatively small (< 120 mm TL) and likely represented age-0 fish <br />(Figs. 6 and 7). We encountered a few bass larger than 120 mm TL (Age 1+), and these fish <br />appeared to be relatively healthy and in good condition. Green sunfish collected in samples were <br />also dominated by relatively small fish (< 80 mm TL) that were likely age-0, although relatively <br />large specimens were captured occasionally (Figs. 8 and 9). <br />Additional sampling was conducted in eight backwaters in spring 1998. A total of 3,338 <br />fish were removed from the eight backwaters with the most abundant species being sand shiner, <br />-11-