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ACQUISITION OF HABITAT PREFERENCE DATA BY RADIOTELEMETRY by Harold M. Tyus U.S. Fish and Wildlife Service 1680 West Highway 40, Room 1210 Vernal, UT 84078 INTRODUCTION Underwater radiotelemetry is a relatively new and rapidly developing methodology for monitoring fish behavior in the natural environment. Its use is particularly recommended in riverine and other systems where some types of biotelemetry may be u:;suit~,ble (Stasko and Pincock 1977). Beginning in the late 1960's (Winter 1983), radiotransmitters were designed for underwater application, and many fish species were monitored in the 1970's with externally and internally attached radios (reviewed by Tyus 1982 and Winter 1983). Radiotelemetry has been used primarily for fish movement studies but has seldom been used for microhabitat determinations. However, fish radiotelemetry offers great promise for microhabitat studies, especially with the use of surgically implanted internal transmitters (Chamb:~rlain 1979), which avoid the abnormal behavior previously observed in some telemetered fishes using external transmitters (Ross and McCormick 1981; Mellas and Haynes 1985). Fish radiotelemetry is most difficult for migratory species and adverse riverine environments, e.g., high conductivities, changing temperatures, and variable flow regimens (Tyus 1982). Radiotelemetry may be the least biased method for obtaining habitat utilization data in such environments, however, since gear selectivity is avoided and the same fish can be monitored for long periods of time. Few investigators have evaluated relative radiotracking success, and no standard criterion is used for comparing radioracking efforts between investigations. A method of success evaluation under different environmental conditions or for different tracking methods would aid others in the selection of gear, and provide insight into manpower needs. This paper is divided into two main parts: part one provides a theoretical background in fish radiotelemetry; part two uses a case study to evaluate radiotracking success, to relate habitat utilization data obtained from radio- tracking to the Instream Flow Incremental Methodology (Bovee 1986), and to discuss data partitioning. The radiotelemetry of the migratory Colorado squawfish (Tyus 1985) in the Green River of Utah provides an example of a large predator that is difficult to radiotrack because it lives in a large 137