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I I I I I , 1 I I j J I I I I t . I I METHODS Electrofishing Four electrofishing trips were made in 1993 on the San Juan River. Trips were conducted in April, May, July, and October (Table 1). The April and May trips sampled the lower part of Reach III, from just above the Mixer to Four Corners Bridge (RM 136.6-119.2). The July trip sampled Reaches I and VII. The October trip sampled Reaches II through VI. The April and May trips were conducted specifically to implant radio tags into adult Colorado squawfish for an intensive radio-telemetry study conducted in the summer of 1993. With the exception of rare fish species, and Floy-tagging of channel catfish and common carp for the nonnative fish study, no other fish community data was collected on these two trips. The July and October trips followed the sampling protocol outlined below. A variety of electrofishing boats were used on different sampling trips (Table 8 in Appendix I), but sampling techniques remained constant among trips. Electrofishing proceeded downstream in a continuous fashion from put- in to take-out. One or two netters stood on an elevated platform above the anodes and collected fish as they were drawn into the electrical field. The raft operator maneuvered the boat via oars, monitored the Variable Voltage Pulsator (VVP), and made adjustments to current, voltage, amperage, frequency, and pulse width when necessary. On trips with only two electrofishing rafts, one raft shocked along each shoreline of the river, breaking off into side channels when necessary. When three boats were used, the third boat worked in tandem with one of the shoreline boats. In narrow stretches of river, all three boats worked abreast of one another, covering the entire channel. When one of the shoreline boats entered a secondary channel, the third electrofishing boat shocked the main-channel shoreline until the first boat reentered the main channel. The study area was divided into five-mile sections, with the first four river miles of each section considered non-designated (NO) miles and the fifth mile considered a designated mile (DM). Sampling technique was the same for OM and NO miles. Electrofishing crews began at the upstream end of each mile and collected all the fish they could net as they shocked downstream. All non-target fish collected in NO miles were enumerated by species and returned to the river. All non-target fish collected in OM's were weighed (g), measured for total and standard lengths (mm), and sexed (if possible) before being returned to the river. Channel catfish and common carp were FLOy-tagged before release for another study. Trammel Netting Trammel nets (one-inch mesh) were used on a limited basis during all sampling trips. Because of the need to cover a minimum number of river miles each day, trammel nets could not be set in anyone area for long periods. Nets were set across the mouths of a backwaters, slow-moving side channels, or mouths of a tributaries (e.g., Mancos River mouth). After a net was in place, 5