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Colorado pikeminnow that were less than 500 mm. Although the MCFT-7A transmitter had a life span less than the smaller transmitter, the advantage of the MCFT-7A transmitter was that it had a larger battery that emitted a stronger signal than the smaller transmitter, which had a smaller battery (3-voh). Receivers. LOTEK® model SRX 400 receivers used to monitor movements of transmitter-tagged fish were of two types. One was a field data logger, version W16 data processing and storage system These receivers were used in conjunction with a Digital Spectrum Processor (DSP) unit and an antenna switcher to simultaneously and continuously scan all aerial and underwater antenna and report signals from tagged Colorado pikeminnow. This reduced the scan time which ;nim;~ed the ldcel~hood of missing several tagged fish that might occupy a location for a short time simultaneously. Each receiver, DSP, and antenna switcher was enclosed in a weather-proof container and powered by a photovoltaic panel and 12-v deep cycle battery. Receivers and antennas were deployed at a remote, land-based telemetry site to constantly monitor the presence and movement ofradio-tagged fish within predetermined tracking zones. Aerial antennas were oriented in a perpendicular direction toward the water flow of the river or canal. When aerial antennas were positioned in a specified direction toward the river or canal, this allowed radio signals to be detected within a specified zone or radius. The greater the number of filaments in an aerial array, the narrower the radius that a radio signal from a tagged fish could be detected by individual antenna (i.e., the greater the directionality of the antenna). The use of two antennas in tandem at each land-based tracking site allowed researchers to discern when aradio-tagged fish passed the station and the longitudinal direction of aradio- tagged fish, i.e., was the fish moving down- or upstream [canal]. Therefore, data recorded from these sites provided fish position relative to a particular antenna. This surveillance technique provided an automatic means of constantly and simultaneously monitoring and storing unique codes of tagged fish. These data along with data collected from monitoring from boats and vehicles increased the number of contacts which ultimately allowed researchers to locate and more confidently follow the movements ofradio-tagged Colorado pdceminnow during this study. The three land-based tracking stations were strategically placed, one on the canal and two along riverine reaches. One data-logging station was deployed in May 2000 at Island Acres State Park (RM 192.3) on the Upper Colorado River, which is about 1.4 miles downstream from Government Highline Diversion Dam, Two additional semi-permanent, land-based tracking stations were deployed during March 2001. One was deployed on the Colorado River (RM 187.2) between Price-Stubb and GVIC Diversion dams and the other was deployed on the Govenn~nt Highline Canal west of Cameo, Colorado. The stations at RM 192.3 and 187.2 each 10