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1 Colorado River RK 348.5 if you happen to be downstream of the confluence. This section of river/lake was surveyed three times (July 1 and 14, and August 12). One 3-day survey was made in Cataract Canyon rapids on July 13-15. The remaining five surveys were made upstream of Mineral Bottom and Potash Boat dock. These surveys included the Green River from RK 81.9 to 218.4 and the Colorado River from RK 77.1 to 160.6. A total of 452.9 km of river was surveyed for study razorback suckers. Throughout this section of river, an average sampling effort of one fish was located every two boat-hours. Alternatively, aradio-equipped fish was located every 53 km of river. Transmitters that were shed or otherwise immobile were not included in the effort estimation. L Habitat Use Each time a razorback sucker was located, habitat type, surface water velocity, and water depth were estimated. Habitat was divided into four categories: channel, near shore, eddy pool, and backwater, and described below: 1. Channel -Defined as the deepest, and most often swiftest portion of the river. Both the Green and Colorado River channels were typically greater than 3 m in depth and surface currents greater than 5 km/hr. ~ 2. Near shore - Defined as river habitat within 10 m from shore. If a fish was within 10 m of shore, but was also determined to be in the main channel or in a eddy, then the fish would be considered to be utilizing the alternative habitat type and not be considered neaz shore. 3. Eddy pools -Formed by water returning upstream, typically near shore, which then enters back mto downwazd flowing currents. Eddy pools are typically oval in shape with the long side pazallel to the main channel. Water flows quickly azound the perimeter of the pool (referred to as an eddy fence), but never as swift as the main channel, with very slow moving water found in the middle of the eddy pool.. 4 B k M . ac waters - ost of the backwaters that exist in the study reach are naturally occurring areas of still water found in flooded canyon mouths. Backwaters are typically 15 cm to 1.25 m deep and can wind nearly 0.3 km up a canyon from the main river. These regions are devoid of current, are not as turbid as the main river, have heavily vegetated banks and margins (dominated by tamarisk, Russian olive, and willow), have slightly warmer water, and more productive plankton communities than found in their associated river (Mabey 1993). However, these regions aze subjected to ,, annual drying during the descending phase of the hydrograph, as well as being subjected to unpredictable flash floods during the summer monsoon season. t 1