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SUMMARY AND CONCLUSIONS Radiotelemetry of stream fishes is a relatively new methodology that offers great promise for microhabitat studies, especially in high turbidity rivers where visual observations are impossible. Radiotracking in high conductivity waters of 400 umho or more is marginally successful, but fishery workers can improve radio reception by understanding radio wave propanation in water and by using the most suitable equipment. Radiotracking is more successful in shallow rivers, and species like suckers, which select deeper habitats, are harder to track. A field evaluation of different radiotransmitters indicated that the performance of fish mt;dules was the same for two different manufacturers and for mercury- and lithium-powered radios. Success of radiotracking was evaluated relative to tracking duration and was similar for three different studies in the Green River basin. Growth rates of recaptured fish suggested that surgically implanted radios should have little effect on the behavior of the fish, and investigators should evaluate growth rates for this purpose. Fish location and habitat use was not difficult to obtain with radio- telemetry, and the results of this study suggested that habitat data obtained by radiotelemetry were nonbiased and representative. Statistical testing between habitats recorded f r fish captured electrofishing and for habitats measured for radiotelemetered fish indicated the two resultant datasets were significantly different, with respect to habitats, substrates, and depths. It is assumed that these results are due to bias inherent in electrofishing data. Because of the large number of contacts that can be made by radiotracking fish, enough data points can be obtained to partition habitat use according to fish behavior, especially by season or habitat heterogeneity. Additional habitat me surements can be made and used to validate the application of physical habitat modelling methodology. This study indicates that a proper interpretation of fish habitat utilization in heterogeneous habitats may require more hydrologic information than is generally collected in physical habitat studies. ACKNOWLEDGMENTS This paper presents the results of research supported by the Fish and k'ildlife Service and Bureau of Reclamation, U.S. Department of the Interior. Many F'sh and Wildlife Service employees aided in data collection and analysis. Carl L. Armour and Ken D. Bovee encouraged the development of this paper and an earlier one on radiotelemetry. Thanks are given to K.M. Paulin for aiding in data analysis, and to L.A. Trinca and C.A. Karp for their suggestions to the draft manuscript. 154