Biotelemetry has been defined as “the instrumental technique for gaining and transmitting information from a living organism and its environment to a remote observer” (Slater 1965). Biotelemetry typically utilizes wireless transmission of either an audible signal or electronic data to determine location of a tagged animal. Fisheries researchers use location information to gain a variety of insights into migration, habitat use, behavior, productivity, or survival of fish. Biotelemetry can be divided into two basic categories, acoustic or radio, based on mode of transmission, mechanical or electromagnetic energy, and operating frequency. Most acoustic systems in use today transmit at low frequency, between 30 and 300 kHz, while most radio systems transmit at very high frequency, between 30 and 300 MHz (Sisak and Lotimer 1998).

Acoustic telemetry is based on the principals of sonar (sound navigation and ranging), which was developed to detect submarines during World War I. The properties of acoustic systems favor their use in deep waters with high conductivity and low turbulence (Winter 1996). Radio telemetry is based on the principals of wireless radio communication, which were first demonstrated by Nikola Tesla in 1893. Radio systems are best suited in shallow waters with relatively low conductivity but have the added benefit of improved signal detection in turbulent conditions and with aerial antennas. Advances in both technologies have resulted in highly efficient transmitter and receiving systems.

Advancements in products used for animal telemetry over the past 50 years have generally followed those in the electronics field (Figure 1). Bell Laboratories1 ushered in the age of digital electronics with the invention of the transistor in 1947 (Mann 2000). Today transistors are common in everyday items such as radios, televisions, hearing aids, computers, cell phones and even MP3 players. Consumer demand for inexpensive small electronic devices with increased functionality has continually driven advancements in the field of electronics. These advancements have subsequently led to improvements in biotelemetry transmitters and receivers such as miniaturization of components, increased battery performance, and more powerful micro-processing.