7039 - Laserfiche WebLink

Home Browse Search

164 UTAH ACADEMY PROCEEDINGS, VOL. 45, PART 1, 1968 The remaining seven groups are common in the Intermountain area and their discovery likely reflects the paucity of previous collection efforts in the Green River rather than recent invasion. Of the 11 different types of Baetis nymphs collected little can be said. Some may be invaders from cool tributaries and others may be previously reported but undescribed species. Edmunds and Musser, (1960) reported one undescribed and one unidentified species of Baetis in the Green River. The undescribed species has flattened, shovel-like claws and was frequently found in the present study (Baetis sp. VII). It is possible that the unidentified form mentioned by Edmunds and Musser (1966) was among the remaining 10 forms of Baetis collected during the present study. DISCUSSION With increasing distance below the dam, atmospheric in- fluences and the addition of tributary waters combine to return the Green River toward a semblance of its preimpoundment state. The river environment at Little Hole was greatly altered following closure of the dam while at Carr Ranch and Echo Park the river showed signs of transition to its fonner state. At Island Park, the Green River appeared to be much the same in 1964-65 as it was before Flaming Gorge Dam was closed. The bottom-fauna community at Little Hole is now a simple one in terms of number of forms present. It is, of course, difficult to say whether this was due to the fish-control project or to closure of the dam. In light of the rather complete recovery of bottom fauna above Flaming Gorge Reservoir (Binns, 1965), where the river environment had not been greatly altered, it seems likely that ecological changes due to the operation of Flaming Gorge Dam were primarily responsible for the changes observed in the bottom-fauna communities. The nearly complete failure of the summer generation of Baetis sp. I in the first 11.7 km of river below Flaming Gorge Dam in 1967 was related to high flows and low water tempera- tures. The observation that 90 percent of the nymphs at Little Hole in October were newly-hatched supports the hypothesis that low water temperatures delayed hatching until temperatures began to rise, during fall overturn in the reservoir, to levels required to complete development. Needham et al. (1935) reported that low water temperatures delayed the hatching of Baetis eggs, but they did not determine minimum hatching or lethal temperatures. i I...