Factors affecting detection probability and range of transmitters and receivers designed for the Juvenile Salmon Acoustic Telemetry System

Acoustic telemetry allows collection of data on the movement and survival of fish and other aquatic organisms. The passive form of this technology uses transmitters (tags) and fixed receivers to record when an organism is present at a given location. Understanding and interpretation of these data depends on knowledge of the detection range and detection probability of the receivers. This study examines factors affecting performance of tags and receivers designed for the Juvenile Salmon Acoustic Telemetry System (JSATS) at a location in the Sacramento River in CA, USA. A group of tags (n = 13) of two power output levels, each transmitting a unique code at five second intervals, were manually moved past a set of two fixed receivers in upstream and downstream directions along transects of different distances from the receivers at two different speeds. The factors that significantly affected detection probability were tag orientation and tag movement direction. Tag orientation had the largest effect on detection probability, with higher detection rates when the tag's piezoelectric transducer was directed towards the receiver. Detection probability (proportion of transmissions detected) was 30-50% out to 160 m. Detection efficiency (proportion of tags regarded as present) was 99-100% when tags passed within 25 m and 84-96% within 135 m of a receiver. These results have implications for the design and interpretation of acoustic tracking studies and the orientation of transmitters when implanted into fish.