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30 I I I I I I I I I I I I I I I I I I I and rotifers (Papoulias and Minckley 1992). Soon afterward, the razorback larvae began to select larger organisms such as zooplankton (primarily cladocerans). The density of zooplankton needed for larval razorback sucker survival (20 organisms per liter of water; Papoulias and Minckley 1990) occurred in flooded bottomland habitats along the Green River but rarely reached that density in backwaters, and never reached it in the river (Mabey and Schiozawa 1993). The decline in razorback suckers and the near extirpation of the bony tail in the upper basin may be linked directly to low or lack of larval survival in these species. Therefore, flooded bottomland habitats are important to some, if not all, of the endangered Colorado River fishes in the upper basin. Zooplankton produced in productive off-channel habitats such as flooded bottomlands also provide food of the proper quantity and size at the right time needed for larval survival of endangered fishes that occupy main channel habitats such as the Colorado squawfish and humpback chub. F. Loss of Critical Low Water Velocity Habitats such as Flooded Bottomlands in the Upper Colorado River Basin. Flooded bottomland habitats occurred along low gradient river reaches with broad valleys. In the upper basin, these reaches have been channelized by levee development to contain the river near population centers and agricultural areas (Bestgen 1990). It is hypothesized that the loss of flooded bottomlands is one factor has adversely affected the food base required by larval endangered fishes. The lack of recruitment of the endangered Colorado River fishes is believed to be linked to predation by nonnative fishes and starvation. Habitat enhancement of the bottomland habitat site described in this conceptual management plan will help to restore needed food resources that should result in better survival of larval and juvenile endangered fishes. DEVELOPMENT ALTERNATIVES Wetland Flow-Throuqh Alternative Objectives: 1) Provide potential spawning habitat for adult razorback suckers; 2) provide nursery habitat for larval razorback suckers; 3) provide wintering habitat for all age classes of razorback suckers. This alternative would take advantage of natural inlet and outlet locations to allow water from the Green River to flow through the wetland during high water levels. Razorback suckers would enter the system at the inlet during high water levels, remain in the wetland to spawn or for a period of growth (250 rom as specified by stocking protocol) and then re-enter the river system through the outlet.