Figure 1. Radio (upper four) and sonic (lower three) tags and their typical size ranges

ERDC TN-DOER-E18

February 2005

Figure 1.

Radio (upper four) and sonic (lower three) tags and their typical size ranges (manufactured by

Lotek)

Radio Telemetry and Transmitters. Radio transmitters emit radio signals from wire antennas

through water and into the atmosphere. Transmissions are received with tuned antennas of

varying sizes and designs. Radio tags typically operate at high frequencies (20-250 MHz) and are

the preferred method in freshwater environments of low conductivity. A significant advantage of

radio tags as compared to acoustic transmitters is that radio signal transmissions are less affected

by physical obstacles, turbidity, turbulence, and thermal stratification (Thorsteinsson 2002).

Transmission of signals by radio tags may be either pulsed or coded. Pulsed radio tags transmit a

simple ratio pulse at set intervals to a radio receiver, while coded radio tags contain a

programmable micro-chip, which can transmit a digitally encoded radio signal at user-defined

intervals to a decoder or recorder. Radio telemetry has been successfully used to evaluate fish

passage efficiency through hydropower facilities, presence and movement within riverine

systems, migration patterns, response to behavioral guidance structures, habitat utilization and

entrainment studies.

Habitat preferences of the target species must be considered before selecting radio telemetry as a

monitoring option. If the species of interest spends a majority of time at water depths >5 m, radio