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METHODS Colorado squawfish used for radiotelemetry were collected by electrofishing. Sampling was conducted in the Yampa River in April and May. 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 individually tied off (usually five) rather thana continuous suture 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. No ill effect of the surgery was noted. Implanted transmitters were Smith-Root Company fish modules dipped in melted beeswax. These modules weighed approximately 11 9 and were of "padlockll 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 and pulse rate) so that individual fish could be identified. Radio receiver sets used were Smith-RootRF-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 IIsearchll type and received all emitted frequencies in the range. Omni-directional whip and bi-directional loop antennas were employed. 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 on boats, or mounted directly to. an airplane wing or landing strut of a helicopter. Smith-Root bi-directional loop antennas were used only to triangulate fish location from boat or shore. .. 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 12 day interval. The location of a fish was recorded as a single contact when encountered. The second method, used only in 1981, 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 h basis as follows: 4