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DISCUSSION Recent research has focused on the benthic macro invertebrate communities in the Green River (Wolz and Shiozawa 1995, Jordan 1996). Zooplankton communities have not been similarly studied and where results are published, they are from the upper Green river at the Ouray National Wildlife Refuge or at Island Park in the Dinosaur National Monument (Grabowski and Hiebert 1989, Mabey 1993). Furthermore, these zooplankton studies were conducted in the summer and fall months, time frames beyond which are considered crucial for larval razorback sucker development. This study evolved because of speculation that there may be a breeding population of razorback suckers in the lower Green river. If this is true, quantification of zooplankton communities in backwater sites where these larval fish must seek haven, is paramount to successful management of the population. Papoulias and Minckley (1990) studied the effect of ration size on mortality and growth of razorback sucker larvae in laboratory experiments consisting of jars of larvae which were fed brine shrimp at concentrations of5, 10,50, 100,500 and 1000 nauplii/L. They found that razorback sucker larvae reared under laboratory conditions passed a critical period between 8 and 19 days of age when shifting from endogenous (yolk) to exogenous (zooplankton) nutrition. Those larvae reared at 5-10 nauplii/L did not obtain sufficient food during this critical period, resulting in> 80% mortality 20-30 days after hatch. Larvae fed 50, 100, 500 and 1000 nauplii/L all had < 20% mortality. Death rates leveled only when larval mortality was sufficient to provide survivors with at least 10-20 nauplii per fish in the 5 and 10 nauplii treatments. If20 organismslL can be considered the threshold below which maximum death occurs in a natural system, then data presented here suggest that larval fish in the three backwaters studied are possibly starving. Zooplankton populations peaked at only 19 organismslL in Anderson and 26 organismslL in Holeman on the final sample in early summer when conditions are conducive to zooplankton growth. All the other sample dates averaged only 6 organismIL. Zooplankton populations in Millard peaked earlier, reaching 29 organismslL by 22 May and 30,53, 124 and 96 organismslL for the remaining sample dates. However, zooplankton levels during the first three weeks of May in Millard were low, with an average of 6, 1 and 8 organismslL respectively. The Papoulias and Minckley studies (1990, 1992) do not account for benthic feeding, nor is there a similar threshold (organisms/cm2, organisms/m2) in the literature for benthic organisms. The data presented herein suggests an abundant population of benthic invertebrates at all sites and dates. These findings are consistent with those late summer benthic studies reported by Wolz and Shiozawa (1995), Mabey (1993), and Jordan (1996). In fact, higher densities of benthic organisms were found in this study during the early spring than were reported from the summer months. Nematodes dominate the benthic samples which is consistent with what is to be expected from calm, stable backwaters with high silt loads. But while quantity of invertebrates may be satisfactory, 13