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Acoustic Transmitters

JSATS transmitters (Figure 1) come in a variety of sizes, weights, and pulse rate intervals (PRIs) to accommodate a range of fish sizes, study durations, and study objectives. The smallest available transmitter to date measures 12 mm long x 5 mm wide x 4 mm high, weighs 0.43 g (in air), and has an estimated tag life of 20–84 days (depending on the PRI; Table 1). The largest, longest-lasting transmitter weighs 1.1–1.2 g and has an estimated tag life of 237–330 days. Transmitters used in 2008 were manufactured by Advanced Telemetry Systems.

Each JSATS transmitter is encapsulated in an epoxy resin and outer Parylene coating and consists of two silver oxide batteries, a circuit board, and the transducer. Transmitters are activated by sending a coded signal to the transmitter via a “pinger dish” (Figure 2). Once activated, the transmitter emits a uniquely coded 31-bit binary phase-shift keyed signal, which provides more than 65,000 individual tag codes. The signal is emitted at a frequency of 416.7 kHz and at a source level of approximately 156 dB (relative to 1 µPascal and 1 m). The length of time between signals is determined by the user-defined, pre-programmed PRI. Pulsing signals use less energy, which increases the life of the transmitter compared to continuous signals.

Figure 1. 2008 Juvenile Salmon Acoustic Telemetry System transmitters. JSATS transmitters are shown in relation to a PIT tag (bottom; Destron-Fearing Model TX1411ST) commonly used in the Columbia River basin.

Figure 2. "Pinger dish" used to activate JSATS transmitters.