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<br />OJ2J96 <br /> <br />14 <br /> <br />the benthic standing biomass in the Colorado River has increased over that which developed <br />under fluctuating flows. <br /> <br />Fisheries <br />The Colorado River and its tributaries in Grand Canyon currently support four of eight <br />historic species of native fishes, including humpback chub (Gila cypha), flannelmouth sucker <br />(Catostomus latipinnis), bluehead sucker (c. discobolus), and speckled dace (Rhinichthys <br />osculus). Fewer than 10 razorback sucker (Xyrauchen texanus) have been captured in the last <br />10 years, and most of these showed evidence of hybridization with flannelmouth sucker. <br />Colorado squawfish (Ptychocheilus lucius), bonytail chub (G. elegans), and roundtail chub <br />(G. robusta) were extirpated soon after Glen Canyon Dam was completed in 1963. Since <br />1958, a total of24 non-native fish species have been reported to exist in the Colorado River <br />of the Grand Canyon (Valdez and RyeI1995). The most abundant species today include <br />rainbow trout (Oncorhynchus mykiss), carp (Cyprirrus carpio), fathead minnow (Pimephales <br />promelas), and channel catfish (ktalurus punctatus). <br /> <br />. The role of backwaters as nursery habitats for young native and for non-native fish has <br />been studied by the Arizona Game and Fish Department and by Northern Arizona University <br />researchers in 1996 and 1997. Stevens et aI. (1997, unpublished) reported that a large return <br />current channel backwater near mile 55.5R was not scoured by the 1996 Test Flow. and was <br />reduced in size by 50% to 80% across the range of ROD flows. The backwater received <br />nitrogen-enriched groundwater and it warmed dramatically during the summer months. The <br />benthic flora and fauna recovered over the 1996 growing season, but plankton density <br />remained extremely low. This backwater supported larval and young native flannelmouth <br />suckers and speckled dace during the spring and early summer. Non-native carp spawned <br />twice (in mid-summer 1996 and early spring 1997) during the study period. <br /> <br />Final Draft " 12/12/97 - For AMWG Review <br />