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connectivity to the river floodplain. Energy dynamics and food production are strongly dependent on floodplain habitats in which shallow littoral zones containing rich organic matter yield much higher densities of zooplankton than habitats in river channels (Hynes 1970; Welcomme 1985, 1989). l Zooplankton densities in Ouray National Wildlife Refuge floodplain habitats were 300 organisms/liter, 10 times those found in adjacent river backwaters during spring (Mabey and Shiozawa 1993). Razorback sucker spawning observations On the middle Green River, razorback sucker congregate at the spawning bars just prior to peak flows about 16 kilometers (km) upstream from Jensen, Utah (Figure 4) and on the lower Yampa River 0.8 kin above its confluence with the Green River (Tyus and Karp 1990). The Green River spawning site located near river kilometer 500 appears to be the most heavily used with over 71% of all captures of razorback sucker in spawning condition from the Green River being from this location (USFWS data base, Vernal Field Station, B. Haines, pers. comm. 1997) Other spawning sites exist, such as the small cobble bar located at river km 492, but size may limit larval 1 production (Figure 5a). "J In the middle Green River spawning usually begins after spring flows start but before spring peak flows. Temperature averages 14 C (range 9-17 C) through the spawning period (Tyus and Karp 1990). Ripe adults were collected over coarse sand substrates and in the vicinity of gravel or cobble bars with an average water depth of 0.63 m. (Tyus and Karp 1990). Average velocity over the bars was 0.74 in s''. On the Yampa River spawning site 6. a velocity associated with spawning fish is 0.3 m s'' at depths of 0.7-1.0 in (McAda and Wydowski 1980). Direct observation of spawning behavior on the middle Green River sites was not made because of high turbidity (Tyus 1987). Razorback sucker females with anal fins almost completely worn off have been 12