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1102 MODDE ET AL. TABLE 2.-Number and biomass of fishes collected during the draining of Old Charley Wash between 25 September and 12 October 1995 and between 17 July and 19 August 1996. Species Age 1995 Biomass (g) Year Number 1996 Biomass (g) Number Northern pike Esox lucius >1 1,620 1 0 0 Common carp >1 7,847,533 13,134 4,297,102 8,778 0 1,399,586 64,959 908,110 134,687 Fathead minnow Pimephales promelas <1 and ?1 476,286 447,617 210,414 267,929 Speckled dace Rhinichthys osculus <1 and >1 2 2 Utah chub Gila atraria <1 and ?1 847 25 144 325 Roundtail chub Gila robusta >1 59 1 45 1 Red shiner Cyprinella lutrensis <1 and ?1 35,857 43,569 28,134 22312 Colorado pikeminnow Ptychocheilus lucius 1 294 7 152 6 Sand shiner Notropis stramineus <1 and >1 0 0 625 1,365 Miscellaneous minnows <1 and 1 10,896 9,020 NA- NA Razorback sucker >1 2,333 2 0 0 0 252 28 188 45 Flannelmouth sucker Catostomus latipinnis > 1 515 6 423 8 White sucker Catostomus commersoni <1 and ?1 515 10 63 3 Channel catfish >1 90,280 687 57,177 218 0 298 185 5 1 Black bullhead 0 62,464 19,636 38.141 3,313 >1 16,774 183 10,383 108 Brook stickleback Culaea inconstans <1 and ?1 1 1 45 35 Green sunfish >1 125,690 3,287 7,642 225 0 43,535 27,092 94,404 103,044 Black crappie 0 16,348 2,321 55,967 6,327 >1 1,666 31 1,223 6 All species 10,133,649 631,802 5,710,389 549,032 I Not applicable (all small cyprinids identified in 1996) zorback suckers reared in several isolated back- waters of Lake Mohave averaged between 20 and 35 cm after one growing season (Mueller 1995). Although growth rates are lower in the Green River system, nearly optimal temperatures and abundant zooplankton in Old Charley Wash provided suit- able nursery habitat for larval razorback suckers. Later in the spring, abundant submerged vegeta- tive growth in the wetland provided cover and food for juvenile fish. Bestgen (1990) reported that aquatic insects and benthos were probably more important to the diet of juvenile and adult riverine razorback suckers than were zooplankton. Because immature razorback suckers tend to conceal them- selves in vegetative cover (Mueller and Marsh 1998), which maintains high densities of macroin- vertebrates (Mabey 1993), floodplain wetlands like Old Charley Wash create environments more con- ducive to growth and survival than main-channel habitats. Heck and Crowder (1991) reported that plant biomass provides both increased food avail- ability and protection from predators for fishes, particularly in closed systems such as disconnect- ed floodplain depressions. Together with an abun- dant food source, the phytophilic behavior of ju- venile razorback suckers may offer the greatest opportunity for this species to recruit despite the large number of nonnative fishes in the Upper Green River basin (Tyus et al. 1982). Collection of juvenile razorback suckers from our study area suggests that similar floodplain wet- lands can be important nursery habitats. However, the timing and duration of flows are critical in allowing larvae access to such habitats. Larval ra- zorback suckers first appear in the main channel during peak flows and are present for up to 6 weeks (Tyus 1987; Muth et al. 1998). The average bank- full flow in the Ouray area is 575 m3/s (Flo En- gineering 1996). The reduced magnitude of spring discharge following construction of Flaming Gorge Dam dramatically reduced the access of lar- val razorback suckers to floodplain wetlands. Without access, most larval fish would remain in the channel after flows recede below approxi- mately 575 m3/s. Thus, both the timing and the duration of the flow released from Flaming Gorge Dam are important in determining larval fish ac- cess to floodplain wetlands. Although the decline of razorback suckers in the Green River basin was coincident with substantial