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1 Selective Withdrawal Structure (Continued from Page 7) structure may reduce potential impacts by allowing time between operations for the system to rebound. A major concern is that warmer mainstem temperatures may be conducive to non-native fish species, allowing non-native species to outcompete native fishes for habitat and food, and even prey upon them. The situatiop may be exacerbated by a low, steady flow regime which would replicate environmental conditions under which many non-native fish species evolved. The eggs and young of humpback chub and other native flSh will need to be protected following successful spawning to enable native flSh to survive and grow to a size where they can compete with the non-native fish. The Adaptive Management Program will serve as the vehicle for refining selective withdrawal operations, as well as identifying, testing, and refining other resource management options and techniques for the native flSh and other resources. The development and utilization of a selective withdrawal structure at Glen Canyon Dam will not, on its own, solve all the problems facing native flSh in the Grand Canyon. However, it could provide a valuable tool for resource managers and an opportunity to further link the management and operations of the dam with the protec- tion, maintenance, and recovery of an important element of the ecosystem for native flSh in the Colorado River. A successful application of a selective withdrawal device requires knowledge of the ecosystem, the species, and the boundaries of the system. Glen Canyon Environmental Studies, Phase II Completion By: Dave Wegner Manager, Glen Canyon Environmental Studies Fiscal year 1995 will be the final year of the Glen Canyon Environmental Studies (GCES) as we presently know it. The plans are to implement a new program--the Adaptive Management Program (see article on page 10) and long-term monitoring. The GCES began in 1982 as an interagency effort to (stated simply) study conditions downstream from Glen Canyon Dam to determine if operations of the dam adversely affected the river-related environmental and recreational resources of Glen and Grand Canyons and if there were different ways to operate the dam. Phase I was completed in 1966, with 39 technical reports evaluating terrestrial biology, aquatic biology, sediment and hydrology, recreation, and dam operations. These studies were conducted during the three wettest years on record (1983-85); consequently, while they provided substantial information on floods, they provided limited information on the effects of powerplant operation. In 1966, the Secretary of the Interior determined that the GCES should be continued to gather additional data on specific operation elements related to the operation of Glen Canyon Dam powerplant. 8 The Phase II research is based on an ecological system approach structured around specific hypotheses and research flows. These studies assess the impacts of low and fluctuating flows and potential impacts to resources and power revenues as well as provide scientific information for input to the EIS. The over 90 technical reports, documents, and data bases included in Phase II studies are scheduled for completion by October 1995. This includes development and integration of computer data bases into the GCES Scientific Information Management System and the Geographic Information System. GCES has served as a template for cooperative, inter- and intra-agency coordination for research and monitoring. At times, GCES has been surrounded by controversy since ecosystems and politics do not mix very well. GCES exemplifies Reclamation's new mission and approach to solving complex ecosystem issues, using a scientific approach in attempting to find the linkages and understanding necessary to provide scientifically based information for the decisionmaking process.