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• UCREFRP Catalog Number: 1113
• Author: Tyus, H. M.
• Title: Acquisition of Habitat Preference Data By Radiotelemetry, ‎(Proceedings of a Workshop on the Development and Evaluation of Habitat Suitability Criteria)‎.
• USFW Year: 1986.
• USFW - Doc Type: \
• Copyright Material: NO

river that has high water conductivities, and turbidity precludes visual
observation.
RADIOTELEMETRY BACKGROUND AND THEORY
The use of radiotelemetry for obtaining physical microhabitat utilization
data on fishes is in its infancy (Tyus et al. 1984), and little guidance can
be obtained from published sources. Bovee (1986) summarized most of the
available information about radiotelemetry for the development of habitat
suitability criteria of stream fishes. This paper expands an earlier paper
(Tyus 1982) providing background information on radiotelemetry, updating
methods, and simplifying theory.
Radiotelemetry has been used to monitor movements and behavior of
terrestrial animals for many years. Earlier workers did not use radiotelemetry
for studying fish movement because it was believed that radiotransmission
through water would be too poor to be effective; they relied primarily on
ultrasonics (Stasko and Pincock 1977). There are, however, several dis-
advantages of ultrasonic tracking. For example, the detection of ultrasonic
signals requires that the receiving hydrophone be immersed in water. This
makes tracking difficult with ice cover and also eliminates the use of air-
craft. Ultrasonic telemetry is markedly influenced by water temperature,
turbulence, and sediment load. Temperature affects the velocity of ultrasonic
emissions, and, in deeper waters, a thermal discontinuity may reflect ultra-
sonic energy away from the hydrophone. Entrained air from waves, boat
propellers, and the movement of bottom sediments caused by stream currents may
cause enough noise to mask ultrasonic reception. For these reasons, radio-
telemetry has been the method most recently used for monitoring fish in large
river systems where visual observation is precluded by turbidity and
conductivities are moderate (Winters 1983).
Radiotelemetry uses a battery-powered radiotransmitter to generate radio
waves (electromagnetic radiation), which are propagated through the water.
This transmitted energy must then cross the air-water interface and be received
by an antenna operating in air. The propagation of radio waves through any
medium, in this case water, is inversely proportional to the frequency. Thus,
radio waves of high frequency travel a given distance with a greater loss of
power than an emission of lower frequency. The nature of the change in
propagation with frequency is approximately logarithmic (Lonsdale 1967;
Lonsdale and Baxter 1968). Radio signals are attenuated (diluted) more rapidly
in water than air, and the amount of attenuation is inversely proportional to
the conductivity of the water (Weeks et al. 1977). For this reason, a
considerable loss of signal strength is expected when radio waves are
propagated through fresh water of high conductivity. Radio transmission in
salt water is virtually impossible.
The behavior of radio energy at the air-water interface (Figure 1) is an
important consideration for radiotelemetry. Energy contacting the interface
is reflected unless the angle of incidence is less than 6° (Weeks et al.
1977). Radiation of the energy that passes this interface produces a signal,
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