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One radio type was monitored for over one year. Mercury-powered modules rated for 1~ years of life averaged 260 days, and five (330) functioned for over one year (455 to 542 days). In spring ,1985, a fish was recaptured (after 12 months) with a defective radio. When this radio was removed from the fish and pounded on a table it began to pulse again and was reimplanted in another fish. The radio was still transmitting after 499 days, when contact with it was lost. Water conductivities during the prime tracking months of May-September, 1980-85, varied from 205 to 950 umho (at 25 °C) and averaged about 540 umho. Fifteen modules experienced temperature extremes from 0 to 25 °C during May 1984 to September 1985. Radiotracking under high conductivities (greater than 700 umho) was marginal, and this contributed to the lack of success in some cases, particularly in deeper water (Tyus 1982) and for razorback suckers, which used deeper habitats in the spring. The relative success of tracking in the Green River was due, in part, to its shallow conditions. In addition, I was able to retune search receivers to obtain greater sensitivity at the expense of not having separate channel bands, and this resulted in better contact success. Highest water conductivities occurred at lowest water levels, and the shallow water levels partially compensated for declining signal strengths. Under these marginal conditions it was necessary to check antenna connections and coaxial cable condition frequently, Poor cable linkages, damaged cables, and connector shorts were the largest contributors to tracking failure. In 1984, all receiving units were refitted from "bnc" to the larger "coaxial" connector, and this aided in reducing connector failure. Simple whip antennas were proven preferable for riverine work, and difficulties in mounting the large 40 MHt Yagi antennas were avoided. Since rivers produce natural boundaries, a directional antenna was not needed until after the general location of, the fish was obtained, After a fish was located by the whip antenna, a small loop antenna was adequate to triangulate fish location. The absolute accuracy of the fish locations from triangulation is unknown. However, individual fish were visually observed in shallow water, and although the fish could not be observed in deep water, depth measurements at the signal source always disturbed the fish. Visual observations and movements of the fish indicated that the signal source accurately pinpoints fish location. Untrained trackers should test their ability to pinpoint transmitter location by using a weighted transmitter. This method was used in training new personnel. The effects of temperature fluctuation on the radio modules was a potential trouble area. The single known instance of transmitter failure occurred during the winter when water temperatures dropped to near 0 °C. I noted deviations in transmitted frequencies (drift) a:~d pulse rates with radio modules. This could have resulted in tracking failure if wildlife-type tracking receivers were used, since these usually have separate and, in some cases, nonoverlapping receiving bands. All SR units were adjusted for maximum signal detection. Although some fish frequencies overlapped, different pulse rates enabled identification of individual fish. Once a radio implanted fish was detected, I was able to tune any 40 MHz frequency with the RF unit and thus confirm each identification. 141