Date of this Version
In 1956 Parker S. Trefethen described an external ultrasonic tag for tracking fish. This tag was designed for use on adult king salmon, Oncorhynchus tshawytsca, and was subsequently used to track these fish above Bonneville Dam (Johnson, 1957). Although this tracking system was the best available at that time several limitations to its use were evident: the transmitter and power supply were large and thus impractical for use on small fish, and the unit was attached externally and was likely to influence movement, and the life of the battery was very short (17 hours). Succeeding transmitters were somewhat longer-lived and smaller (Novotny and Esterberg, 1962). However, they were externally attached to the fish and their use still limited by a short battery life (up to 10 days).