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s Methods Sampling of the river was stratified by river miles which were ~ designated on a base map (U.S.G.S. 7.5 minute quadrangle), with Piute Farms, Utah designated river mile (RMI) zero and subsequent miles numbered upstream (Figures 2 and 3). All data collected were referenced to the nearest 0.1 RMI. The river was blocked into five-mile reaches for standardized electrofishing and seining. The 5-mi reaches were numbered consecutively upstream and assigned Reach ~ Code numbers (e.g., RMI 0-5 = Reach Code 1, RMI 5-10 = Reach Code 2, etc.). Sampling periods were established for: spring (March to June); summer (June to September), and fall (September to December). Fishes were sampled by UDWR with 16 ft rigid-bottom electro- fishing boat or 18 ft raft outfitted for electrofishing, and seines. ~ The rigid-bottom boat was used from Four Corners to Sand Island (RMI 136-87) and the raft from Sand Island .downstream (RMI 87-16; Figures 2 and 3). Power for electrofishing was produced with a Honda EMS4500 generator (Honda Motor Co., Ltd., Tokyo, Japan). Pulsed direct cur- rent was produced with a variable voltage pulsator (VVP-15, Coffelt Electronics Inc., .Englewood, Colorado). Electrofishing was performed ~ along shorelines, in backwaters and tributary mouths during spring and summer. Standardized electrofishing runs began at the most upstream _ RMI (RMI 136.2) and progressed downstream along a single bank until RMI 16 was reached. During spring the right bank was electrofished, and during summer the left bank was electrofished. All fish stunned _ in the first mile of each 5-mile segment were captured with dip nets, ~ enumerated and recorded by species for that river segment. Fish that were missed and could be identified to species were enumerated and recorded. Because of their abundance and relative ease of identifi- cation, carp stunned in the first mile were counted, and no attempt was made to net them. Catch rates (fish per mile, and fish per hour for summer data) were calculated only from standardized electrofishing ~ data. Only rare fishes were captured and numbers recorded in the re- maining 4 mi of each 5-mi segment, although numbers and species of nonnative predator fishes were recorded whenever observed. Rare fish longer that 200 mmTL were given unique numbered, blue Carlin tags. Where multiple channels or islands occurred, only one downstream pass was made through the most navigable-looking channel, and best-looking ~ habitat. Total electrofishing time (seconds}, as indicated on the UVP timer, was recorded for each 5-mi segment. Electrofishing operations were temporarily suspended when suitable shoreline or backwater habi- tats ( ~ 30 m2) were encountered for beach seining. After completion of the standardized electrofishing in spring and in summer, additional target electrofishing was completed. These efforts were directed ~ solely at collecting rare endemic Colorado River fishes. During additional target electrofishing, effort was made to work the areas that appeared most likely to be "Colorado squawfish habitat," or harbor other rare fishes. Electrofishing effort for each 5-mi reach was recorded. Catch rates were not calculated from additional target electrofishing data. - 9 -