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I I I I I I I I I I I I I I I I I I I Valley downstream to the Utah border and included the deep-water area known as Black Rocks. The confluence of the Gunnison and Colorado rivers is in the upper part of Reach 4. Reach 3 was the moderate- to high-gradient reach upstream from Moab (RM 65-110), whereas Reach 2 consisted of the lo~gradient area downstream from Moab (RM 0-65). The Dolores River joins the Colorado in Reach 3. Reach 1, the most do""stream reach, consfsted almost entirely of waters within Lake Powell (RM 168-200), the reservoir formed by Glen Canyon Dam. Methods Radiotelemetry (Objective 1) Movement of adult-size Colorado squawfish was followed using radiotelemetry. Fish were collected by e1ectrofishing, gill nets and trammel nets in early spring, prior to the onset of spawning. After measurements of total length (TL, mm) and weight (g) were taken, Colorado squawfish longer than about 450 mm TL (considered the minimum size of fish suitable for carrying a transmitter) were anesthetized and surgically implanted with radio transmitters following procedures outlined by Miller et a1. (1983). Several transmitter types with theoretical battery life of 6, 10 and 18 months were used. Transmitter weight (in air) ranged from 9 to 20 g. To nrinimize handling stress, radio-tagged fish were released near their capture site within two hours of the surgical procedure. We endeavored to capture fish for radiotelemetry from each of the major river reaches. However, because the study area was too large to allow an effective, annual, riverwide study, the number of fish equipped with radios differed within reaches among years. River reaches were searched for radio-tagged fish at least bi-week1y between April and October and more frequently during the spawning season. Routine tracking was not conducted during the November-March period. Tracking was usually performed by a two-person crew proceeding downstream in a f1at- bottom boat; however, occassiona1, relatively unsuccessful searches were made from aircraft (see Appendix Tables 19-21 for a summary of tracking effort). Larval samD1inq (Objectives 1 and 2) From July through October, which encompases the spa""ing season for Colorado squawfish, the radio-tracking effort was accompanied by qualitative sampling of the larval fish community. Larval fishes were collected in 0.5- mm-mesh hand nets from backwater and shoreline areas at approximately 5-mi intervals along the river. Areas that received extra radio-tracking surveilance because radio-tagged adult fish were present, also received intensified larval sampling. Between 5 and 15 minutes of effort were expended in the collection of each sample. All larval fishes collected were preserved in 5" formalin. These fish were later identified, grouped into 10-mm length classes and counted at the Larval Fish Laboratory, Colorado State University. Locations and dates of larval fish collections are provided in Appendix Tables 22-24. For graphic presentation, data were sunvnarized as the percent composition of all larval fishes collected by week from within lQ-mi river reaches; however, data were grouped within the four major river reaches for statistical analysis. 8