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BR's responsibility under the MOU to provide the hydraulic and physicochemical modeling for the Upper Basin was transferred to FWS in 1980 by amendment. This work was then delegated to the FWS Western Energy and Land Use Team's (WELUT) Instream Flow Group (IFG). A second amendment to the MOU provided for investigation of the humpback chub in the vicinity of the Little Colorado River in the Lower Colorado River Basin, which was concluded in March 1982. A third amendment expanded field investigations to the Dolores and Gunnison Rivers during 1981. A final report for the Dolores and Gunnison studies was completed in February 1982 and is containedin Fart 2, Field Investigation. A study of fish fauna under the MOU with BR included the Upper Colorado River from Lake Powell to Debeque, Colorado, and the Green from its confluence with the Colorado River upstream to Split Mountain Gorge (Figure 1), a total of 575 river miles (RM). A major objective was to determine relative abundance and distribution of the target species an4 to describe the habitats for which they exhibited preferences or wers critical to some phase of their life cycle. In order to meet these objectives and limit bias, a sampling program was developed which avoided bias in the treatment of all habitats and permitted statistical analysis of results. Sampling program design and detailed methods of acquiring data are detailed in Part 2 under the various individual reports. Other field investigations addressed life histories and environ- mental needs of the target fish. These included a description of spawn- ing, migration, disease, tolerances to natural and artificial chemical compounds, interspecific competition, food supply, taxonomy, and preda- tion by striped bass. Water turbidity precluded direct observation, therefore, all hypotheses were extrapolated from fish captures and telemetry. One solution was to directly observe the northern squawfish which inhabit streams of much greater clarity in the Columbia River Basin. The Idaho Cooperative Fishery Unit conducted in situ behavioral studies of the northern squawfish, one of only two closely related squawfish, as a surrogate to the Colorado squawfish. Another approach was to attach radio transmitters to a number of larger fish and to follow their activ- ities with directional radio receivers. Program objectives also included laboratory studies of Colorado squawfish including swimming stamina, temperature tolerance and prefer- ences, total dissolved solids (TDS) tolerance and preferences, and bioassay tests for potentially toxic trace elements. These investiga- tions were contracted to the Utah and Idaho Cooperative Fishery Research Units at Logan, Utah, and Moscow, Idaho, respectively. Included in the overall program was an investigation of the culture of the target species to fulfill the need for laboratory specimens and to • advance cultural technologies. These activities were centered at the Willow Beach National Fish Hatchery on the Colorado River near Las Vegas, Nevada, with satellite programs at the Utah State Fisheries Experiment Station at Logan and Dexter National Fish Hatchery near Roswell, New Mexico. These programs included the use of hormones to induce spawning, incubation of eggs, and rearing of fry and older fish. 2