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w U a u_ ,~'\ `~ ~ .,` ter.-~,~-~ .~ ~ ~ _ ~~ N ~1~ ~, _~ 50 100 150 200 M WHIP WITH GROUND REFERENCE WHIP WITHOUT GROUND REFERENCE ----- LOOP ANTENNA -------- Figure 7. Relationships between relative signal reception strengths for three antenna arrangements and received signal distances for transmitters positioned at the surface, lm, and 2m below the surface. t Sinning (1979) assumed that the water in the Green River was deeper than the water in our study area. Very little of the Green River in our study area was over 2 m deep, although depths of 3 m were encountered. Radiotelemetry was more difficult to use in other stretches of river, especially canyon areas. Fish were located by airplane in Desolation and Labyrinthe Canyons where tracking was not attempted by boat. Our findings that range decreased with increasing depth and conductivity were similar to results obtained by Knight (pers. comm.). Knight has received signals from implanted fish in water with substantially higher conductivities than those 1n our study area, but only where the water was very shallow. The released fish (other than No. 001, which was obviously stressed) tended to remain in the general area of their release, or to return where captured and remain there for weeks. This behavior made them easy to find and study. Also, the fish tended to occupy the shallow areas next to dropoffs, thereby enhancing our ability to locate them. Field workers who plan to use radiotelemetry should carefully consider all factors including equipment limitations; and physiochemical characteristics of water before decisions are made to initiate studies. REFERENCES American Public Health Association. 1971. Standard methods for examination of water and wastewater. 13 Ed. Washington, D.C. 875 pp. Archer, D. L., H. M. Tyus, and R. Valdez. 1980. Field methodologies of the - Fish• and Wildlife Service's Colorado River Fisheries Project. Trans. Bonneville Chp., Amer. Fish. Soc. 1980:13-36. AVM Instrument Co. 1979. Radiotelemetry equipment techniques manual. Champaign, IL. 32 pp. Bidgood, 8. F. 1980. Field surgical procedure for implantation of radio tags in fish. Alberta fish and Wildlife Div., Edmonton, Alberta. Fish. Res. Rep. 20. 9 pp. Holden, P. B., and D. A. Shelby. 1978. A study to determine the spawning requirements of Colorado squawfish. U.S.D.I. Fish and Wildl. Serv. Fort Collins, CO. 29 pp. Knight, A. 1981. Personal communication. U.S. Fish and Wildlife Service. Laconia, NH. Kolz, L. 1980. Personal communication. Denver Wildlife Research Center, U.S. Fish and Wildlife Service, Denver, CO. Larimore, R. W., J. Tranquilli, and W. Cochran. 1975. (No title given.) Underwater Telemetry Newsletter 5(1):6-7. 24 25