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... placed in a recovery tub filled with fresh river water. The fish usually recovered frOm the anesthesia in 2-3 min and were then transferred to holding pens for a 72-h observation period before release. Each fish was also tagged externally with a serially-numbered plastic Carlin tag (Valdez et ale 1981) to identify the fish externally after the life of the transmitter. The eight fish modules transmitted on assigned frequencies ranging from 40.370 to 40.430 MHz. Smith-Root SR-40 Search Receivers and RF-40 Tracking Receivers were used to relocate the tagged fish. A Larson- Kulrod whip antenae was used with the SR-40 receiver to indicate the presence of a fish within the receiving range. The SR-40 has a scanning feature that issues visual and audible cues when any transmitter is located. A SO-ohm directional loop antenae was used with the RF-40 receiver to pin-point the location of a tagged fish by triangulation. The RF-40 is equipped with an adjustable frequency mode and a 2-KHz band- width narrow-range reception. Most monitoring was done from a boat or from shoreline, although one aerial reconnaissance from a Piper Supercub was conducted. Fixed-winged surveillance proved ineffective because of the limited strength of the SM-l modules or the receivers. Water depth and velocity as well as substrate were recorded each time a fish was located and at 1/2-h intervals thereafter until the signal was lost. Depth was measured with either a Lowrance model LRG 1510-A sonar depth finder or an extendible surveyors rod, and velocity was measured with a Marsh-McBirney model 201 current meter. Water temperature (OC) and conductivity (umbos/em) were measured with a Yellow Springs model 33 meter. A transmitter was temporarily implanted in a surrogate species- roundtail chub (G. robusta)--to test the implant procedures and determine the limitations of the search and tracking receivers. The roundtail chub was placed in a nylon-mesh bag, freely suspended with floats and held at varying depths and distances from the receivers. The maximum depth received with both receivers was 6 m from within a 10-m horizontal radius and the maximum range was 195 m at 1 m depth, at about 800 umhos/cm con- ductivity. Use of this radiotelemetry equipment in Black Rocks was restricted by high conductivity and maximum water depths of 18 m. RESULTS AND DISCUSSION Movement Little movement was observed for any of the eight radio-tagged hump- back chub released in Black Rocks. Average movement of these fish was 0.8 km with a range of 0.1-3.7 km (Table 2). These observations were made for periods of 4-93 days starting either 3 Mayor 30 May 1981. The tagged fish monitored for a short duration either left the Black Rocks 32 . I , r I I I I t I i 1 I j I I I t j I j t