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Last modified
7/14/2009 5:02:34 PM
Creation date
5/17/2009 11:49:57 PM
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UCREFRP
UCREFRP Catalog Number
9301
Author
Wydoski, R. S.
Title
Green River Fishes and Invertebrates.
USFW Year
1967.
USFW - Doc Type
Logan, UT.
Copyright Material
NO
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5 <br />DISCUSSION <br />Assessment and assignment of effects of either the fish control project <br />or of the closure of Flaming Gorge Dam upon distribution and abundance of fish <br />and invertebrate populations are difficult to do precisely because pre-im- <br />poundment studies were primarily of a qualitative rather than a quantitative <br />- nature. Some assumptions were made, therefore, and the primary assumption <br />was that pre-impoundment populations of fish and invertebrates immediately <br />below the dam site were the same as those present at Island Park, 78 miles <br />downstream. This appears to be a realistic assumption in that water tempera- <br />ture, turbidity, bottom type and various water quality characteristics were <br />"similar in these two areas before 1962. The modifying effects of the Yampa <br />River entering 12 miles above Island Park were assumed to have been minor <br />in pre-impoundment years since all species of fish collected at Split Mountain, <br />Island Park, and Echo Park were collected at the head of Lodore Canyon and <br />above the site of Flaming Gorge Dam in pre-impoundment years. It was on the <br />basis of these assumptions that pre- and post-impoundment populations in the <br />study area were compared. <br />Another limitation to objective analysis is the fact that no data were <br />available on the nature of the rotenone "block" or "blocks" which passed <br />through Dinosaur National Monument during the fish control operation. The <br />length of the water mass, concentration of rotenone, distribution of rotenone <br />with respect to time and space, and the proportion of the fish population <br />affected.are unknown. The-numbers of fish drifting dead or dying into the <br />Monument from the upriver operation can only be speculated upon. Problems <br />associated with quantitative sampling of fishes in the river habitat largely <br />remain unsolved even though special methods were developed to capture all <br />species present. The best approach was to rank abundance as rare, occasional, <br />common, or abundant. <br />The absence of Gila cypha in pre-impoundment survey collections within <br />Dinosaur National Monument is an indication that the species, whose taxonomic <br />status is not presently clearly defined, was rare in the Green River between <br />Flaming Gorge Dam and Ouray, Utah, before the construction of the dam though <br />it had been found in the reservoir basin at Hideout Flats in 1959. The cap- <br />ture of three specimens of Gila cypha in the study area in 1963 but none in' <br />subsequent years indicates that it remains rare in the Green River within the <br />Monument. Morphological variability among the two forms of G. robusta (G- .E. <br />robusta and G, r. elegans) and the relationships between them and G. cypha in <br />the upper Colorado River drainage are currently being studied jointly by the <br />Utah and Colorado Cooperative Fishery Units. Computerized taximetric programs <br />are being employed, and preliminary findings indicate that strongly-humped <br />forms of Gila from Lake Powell and the Colorado River immediately below Glen <br />Canyon Dam closely resemble G. cypha or possibly may be hybrids between <br />elegans and c ha. These strongly-humped forms are relatively more abundant <br />in the Glen Canyon area than in the Green River, although collections remain <br />to be made in Desolation, Grays, and Labyrinth Canyons in the Green River. <br />Though some of the adult humpback suckers taken in the Green River and <br />in the Yampa River immediately above the confluence were gravid, no evidence <br />of reproductive success was found in either river. These fish may have been
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