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METHODS Zooplankton sampling during 1983 employed the same methodology as 9arley (1967) for relative comparison of current data with that taken in the mid- 1960's. Zooplankton samples were collected monthly from April through October at six pelagic sites spaced over the length of the reservoir. Three _ daytime replicate samples were taken at 0-3.0 m (0-10.0 ft.), 3.1-9.1 m (10.1-30.0 ft.), and 9.2-18.3 m (30.I-60.0 ft.) depths at each location by vertical hauls of a Wisconsin-type closing net, ~d20 silk bolting. Seventy percent ethyl alcohol was used as a preservative. Zooplankton laboratory analysis was executed using a binocular micro- scope and Sedgwich-Rafter counting slide and basically follows "Standard Methods for the Examination of Water and Wastewater" (Am. Pub. Eealth Assoc. 1965). From each concentrated sample random 1 ml subsamples were drawn and completely censused. To assess zooplankton size-frequency distributions, up to 20 randomly selected individuals of each identified taxa of cladocerans and copepods were measured on each slide using a Whipple disc micrometer. RESULTS Table 1 presents abundance (mean number/liter) of 5 common taxa of zooplankton in Flaming Gorge Reservoir for 1965-66 and 1983 on a monthly basis. Daphnia pulex, the large dominant cladoceran, was 2-10 times more numerous in the mid-1960's than in 1983. The Daphnia populations Peaked in June during both the 1965-66 and the 1983 periods followed by a sharp decrease from July through October. The copepod, Diaptomus, was also more numerous in the mid-1960's samples than in 1983. There has also been an apparent shift in species composition within the Diaptomus genera since the mid-1960's. The mid-1960's samples were dominated by Diaptomus clavipes, a large copepod species, while the 1983 samples included few D. clavipes and were dominated by a small form (probabl;~ D. ashlandi). The intermediate sized copepod, Cyclops bicuspidatus thomasi, was also less abundant in 1983 than in 1965-66 from April through July; however it was significantly more abundant from August through October. The common rotifer Polyartha followed the same pat- tern as Cyclops. The rotif er, Kellicottia longspina, was included as an example of a new rotifer that has appeared in the reservoir between the mid-1960's and 1983. The mean size of the cladocerans and copepods from Flaming Gorge Reser- voir in 1983 samples was smaller than that reported by ~Iarley (1979) for 1965 and 1966. Mean size of Daphnia pulex was 1.36 mm in 1965-66, but 1.14 mm in 1983. Diaptomus averaged 1.21 mm in 1965-66 and 0.77 mm in 1983, represent- ing a shift in species dominance. Cyclops bicuspidatus thomasi mean size was 0.92 mm and 0.60 mm in the mid-1960's and 1983, respectively. 15