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sampling scheme was used as in 2000 except a seventh pass was performed in the mid- river zone. The additional mid- river pass was found necessary to improve the recapture probabilities for large fish mid-channel. The dates and the mean daily flow (Palisade gage) for that day for the period of sampling is given in Table 3. The Dolores River was electro-fished in July 2000 and 2001. In both years on the first pass block nets were placed at the downstream end of each run (upstream of riffles). Also, each run was repetitively electro-fished three to five times. Fish from each pass were held in nets, then marked and released into the same run of capture. This process was continued over the entire reach. Block nets were not used on recapture passes. Dates of electro-fishing and flows from the Slick Rock gage is given in Table 3. CHANNEL TOPOGRAPHY Global Positioning Systems and Sonar In 1999 and 2000, bathyrnetric surveys of the channel were taken of the six study sites using Global Positioning Systems (GPS) and sonar technology. The channel surveying technique previously described in Anderson and Stewart (2000) was performed from a moving boat. A large amount of bathymetry data was gathered in a short amount of time. The GPS system was a Javad Oddessy L1/L2 RTK GPS with Glonass and Multi- path reduction options turned on. The system had a published vertical accuracy of 15mm +/- 1.5 mm. The sonar unit was an ODOM Hyrographic Systems, Hydrotrac -Single Frequency, Portable Survey Sounder. The sonar unit used a 200kHZ frequency with a published accuracy of lcm +/- 1% of depth and an output resolution of lcm. The sonar unit pinged and logged ten depth readings per second. The RTK GPS logged one position per second. The RTK GPS system output a NMEA GGA string at a rate of 1Hz while the sonar output text strings indicated depth at a rate of l OHz. Data from these instruments were sent to a laptop computer and recorded using the COMLOG software from ODOM Hydrographic. Because the RTK GPS and Sonar data were received at different rates, all data entries collected by the COMLOG software were time-tagged to the millisecond using the computer's clock. The depth readings immediately before and after the RTK GPS reading were interpolated by the computer clock time (nearest millisecond) to produce the XYZ coordinates used to map bed topography of the river channel. Bathymetric data were collected from longitudinal runs and cross-sectional surveys. Special care was taken to ensure that the transducer and GPS antenna were mounted in such a way as to remain nearly vertical during each run. 25