8062 - Laserfiche WebLink

Home Browse Search

• of rapidly changing land and water uses. The zoogeographical effects of dams and diversions, water storage, irrigation practices, mining pollution, and the introduction of non-native species were thought to be especially im- portant in terms of native fishes' welfare. Today, municipal pollution, introduced fish diseases, and stream bank channelization could be added to the list of suspicious resource developments. Various authors have documented the decline or disappearance of bonytail chubs and razorback suckers from the Green River in Colorado following the closure and filling of Flaming Gorge Reservoir (Minckley and Deacon 1968; Vanicek and Kramer 1969; Holden and Stalnaker 1975). These two fishes sur- vived below the reservoir for a few years after it was completed and was fil- ling with water. During this time, water temperatures and flows below the impoundment were comparable to historic patterns. However, when full, the cold tailwaters created by hypolimnetic reservoir releases significantly lowered the water temperatures downstream. Lack of reproductive success by bonytail chubs, as well as reduced growth, in the Green River was directly correlated to the lowering of riverine water temperatures. Waters which usually reached 700F in late summer did not approach the minimum 650F needed for spawning. A concurrent disappearance of razorback suckers from the Green River was also blamed on reduced water temperatures. In addition, a project to improve trout fisheries by eliminating Colorado squawfish, suckers, and other "trash" fishes above Flaming Gorge Dam resulted in a fish kill downstream as far as Dinosaur National Monument. When detoxification procedures failed, rotenone escaped downstream and numerous razorback suckers and bonytail chubs were killed (Banks 1964). Backwater nursery habitat for larval and juvenile fishes, usually created during spring runoff by the inundation of low-lying areas adjacent to - 7 -