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. . Radiotracking Six scheduled 10-day radiotracking trips were conducted during this investigation (Table 2). An additional preliminary tracking trip of 7 days was conducted to m~e;' with FWS and BOR personnel to standardize radiotracking techniques, ~abitat measurements, and to organize and test equi~nt. The six lO-day trips were conducted from December 12, 1986, through March 31, 1987. Each radiotracking trip involved the use of a fixed-wing aircraft and boats. . . Aerial telemetry. Aerial radiotracking was conducted in conjunction with all seven tracking trips. A Cessna 182 RG fixed-wing aircraft equipped with two omnidirectional whip antennas, an RF-40 receiver, and a SR-40 receiver was used for all aerial radiotracking. One antenna was attached to each wing strut, with the RF-40 antenna on the left side and the SR-40 antenna on the right side. Antenna leads were connected directly to the receivers while headphone leads (to the pilot and passenger) were routed through a switch box that allowed the person monitoring the radios to quickly switch back and forth between the audio from each receiver. Typically, a signal was received on the search receiver (SR-40), and the observer would set the frequency on the RF-40 receiver to the frequency of the fish most likely to be in the area. By switching back and forth between receivers, and setting the RF-40 to the most probable frequencies, the identity of a fish could generally be deter.mined with one or two aerial passes. Locations provided through aerial telemetry were generally w..i.1h.!n 0.1 mile ~ the :eoint subsequently located by boat. Generally, aerial telemetry was conducted at ground speeds of 70-160 mph at above-ground elevations of 50-1000 feet. . . . Ground telemetry. Aerial locations of the radiotagged fish were then given to ground crews. Radiotracking from the ground was done from jonboats and occasionally, from automobiles. The usual procedure involved motoring to the location of a radiotagged fish from the nearest possible launch site. The SR-40 receiver was used in the initial search for the signal. To obtain maximum reception, the omnidirectional whip antenna, mounted to a metal plate 8 feet above the water level was used. The receiver was continuously monitored through headphones while in transit on the river. Once a radio signal was received, the RF-40 receiver and a loop antenna were used to locate the fish in the river channel. At this point the boat was taken to the nearest shore or island, with care being taken not to disturb the fish. From land, the RF-40 receiver was used exclusively; first to identify the fish bydetennining the frequency and pulse emitted by the radiotransmi tter, and then to locate the fish using triangulation. Triangulating the location of a fish involved using the directional capabilities of the loop antenna (null and strongest signal) to set up two or three bearings at different places along the shore. Bearing or sightings were marked with two flagged metal rods put into the ground 10 to 15 feet apart in line with the direction of the null and/or strongest signal. . . . 8 .