Quantifying a Manual Triangulation Technique for Aquatic Ultrasonic Telemetry

Ultrasonic telemetry is widely used to determine the large-scale migrations and movements of aquatic animals, but it can also be used to monitor fine-scale movements and habitat occupancy. We tested the accuracy and precision of a method that manually triangulates transmitter locations from a series of bearings recorded at known observer locations. Bearing estimates were based on the direction of the strongest transmitter pulse received at each stationary position. With a minimum of three bearing estimates, transmitter locations and 95% confidence ellipses were calculated. Testing within a blind experimental design showed that triangulation improved accuracy and precision when additional bearings were used and that it was optimized when bearings were recorded from widespread locations. Using 3-7 bearing positions, 95% of all location estimates were within 34 m of the actual transmitter. Triangulation is best suited for monitoring animals during periods of quiescence, and it can be used effectively to describe the extent of home ranges, spawning areas, and overwintering habitat, among other factors. Understanding the fine-scale habitat occupancy of aquatic animals is critical to species management, and triangulation can provide substantial improvements to the traditional location estimates used in ultrasonic telemetry.