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X METHODS Colorado squawfish were collected primarily by electrofishing; but some were also collected with trammel nets and seining. Sampling was conducted in the Green River in April and May 1980 and in the Green, White and Yampa rivers in April and May 1981. Although cold weather made it difficult to capture fish, collections were made early in the year so fish might have time to recover from surgery before the spawning season. After their capture, the Colorado squawfish were anesthetized with tricaine methanesulfonate (200 mg/L) and surgically implanted with radiotransmitter modules. Surgical procedure was similar to Bidgood (1980) except for several departures. Sutures were individual (usually five) rather than the continuous suture used by Bidgood and the incision was made laterally, immediately anterior and slightly dorsal to the insertion of the right pelvic fin. Each fish was weighed and the total length (TL) measured. The fish were held in river holding pens three to five days before release. No ill effect of the surgery was noted. Implanted transmitters were AVM Company fish modules (AVM 1979) dipped in melted beeswax. These modules (SM-1) weighed approximately 11g and were of "padlock" shape. The units were powered by a mercury (HG-630) battery and had a theoretical life of about 215 days. The units transmitted in the 40.660-40.700 MHz frequency range. Each transmitter had a unique signal (frequency vs pulse rate) so that individual fish could be identified. Radio receiver sets used were Smith-Root RF-40 and SR-40 models. The RF type enabled the investigator to identify any particular frequency transmitted at 40 MHz. The SR receiver was a "search" type and received all emitted frequencies in the range. Omni-directional whip and bidirectional loop antennas were employed (Fig. 2). A Larson-Kulrod whip antenna was used to search for implanted fish. This antenna was mounted on a 20 cm square steel plate elevated about 4 m above the water when mounted on a boat, or mounted directly-to an airplane wing strut or'landing strut of a helicopter. Smith-Root loop antennas were used only to triangulate fish location, from boat or shore. For additional information on radiotelemetry method used see Tyus (1982). It was necessary to use aircraft to keep contact with several fish at one time. The most successful aircraft used was a helicopter, since airplanes cannot safely fly in most canyon areas. The radiotelemetry program utilized two different methods for recording information about habitat preferences and movement. The first method recorded long distance movement by attempting to locate all radiotagged fish on a 1-2 day interval. The location of a fish was recorded as a single contact when encountered. The second method used a diel sampling procedure to obtain more specific information on local movement and habitat preferences. This sampling procedure consisted of observations made continuously on a 24-hour basis as follows: 3