Testing an autonomous acoustic telemetry positioning system for fine-scale space use in marine animals

We tested the capabilities and limitations of a novel autonomous acoustic positioning telemetry system with data from fifteen field deployments off the Florida coast. Telemetry array coverage areas ranged between 100 and 300m across. For fixed transmitters within the array, the fraction of transmissions leading to high-quality calculated position estimates averaged 44%, with wide variation. Positional accuracy was about 2m. The choice of filtering strictness represented a trade-off between the accuracy and frequency of positions. There was substantial temporal variation, but no clear pattern (e.g., daily or tidal correlations) in frequency of positions. There was no spatial bias within the array. Array performance for stationary transmitters was robust to user errors in sound speed and hydrophone position estimates. Performance was less robust for a transmitter attached to an autonomous underwater vehicle moving through the array, with 22% of transmissions leading to position estimates. Overall the system produced reliable results, but as the use of acoustic telemetry in complex ecological studies increases it is important to recognize technological requirements and limitations.