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ISMP backwater sampling evaluation <br />chub, Gila robusta, was the most abundant taxon (1.8 %, n = 707). One Colorado pikeminnow <br />(TL approx. 35 mm TL) was captured and released in 1997 in a sub-reach 3 backwater located <br />approximately 3.2 kilometers downstream of the confluence with the Gunnison River. <br />Centrarchids were 4.9 % of the total number of fish captured; these were mainly green <br />sunfish (4.0 %) and largemouth bass (0.8 %). In all, 1,522 green sunfish (19 to 227 mm TL) and <br />321 largemouth bass (32 to 263 mm TL) were removed from the 21 backwaters sampled in the <br />Grand Valley reach of the Colorado River in autumn 1997. <br />1998 Sampling <br />A total of 24 different backwaters was sampled in the Grand Valley reach of the Colorado <br /> <br />River from 15 September to 17 November 1998. The 24 backwaters represented nearly every <br />accessible backwater habitat in the reach and had an estimated surface area of 16,229 m2. <br />Backwater habitat was again unevenly distributed among the reaches. Sub-reach 1 contained ten <br />backwaters, sub-reach 2 had one backwater, and sub-reaches 3 and 4 contained seven and six <br />backwaters, respectively. One backwater in sub-reach 1 was sampled twice (samples 4.1 and <br />4.2), once each by capture-recapture and depletion techniques, because centrarchid abundance <br />was very high. Thus, a total of 25 abundance estimates were available for the 24 backwaters <br />sampled. <br /> <br />Fish abundance in 22 backwaters was estimated using depletion techniques. Fish <br />abundance in the remaining two backwaters and the sub-reach 1 duplicate backwater was <br />estimated using capture-recapture. Sampling effort included 530 seine hauls, and 1,097 minutes <br />-10-