Mobile Positioning of Tagged Aquatic Animals Using Acoustic Telemetry with a Synthetic Hydrophone Array (SYNAPS: Synthetic Aperture Positioning System)
Julie K. Nielsen, George H. Niezgoda, S. James Taggart, Steven J. Cooke, Peter Anson, Caleb T. Hasler, Kyle C. Hanson, and Gord Carl
Abstract.—We present a new acoustic telemetry method for efficiently estimating positions of tagged marine and freshwater animals using vessel-based active tracking. Vessel-based tracking can require considerable time and effort, which limits both study area size and the number of tagged animals possible for telemetry studies. However, the recently-developed SYNAPS (Synthetic Aperture Positioning System) tracking method allows efficient collection of fine-scale movement information for many tagged animals within large study areas, and therefore enables large surveys to be conducted in a methodical and cost-effective manner. SYNAPS computes position estimates of tagged animals by means of hyperbolic positioning using the geographic location of a mobile hydrophone synchronized with signal detections to create a synthetic hydrophone array. Here we describe the process of tracking with SYNAPS, quantify accuracy and precision of position estimations, and provide guidelines for tracking procedures. SYNAPS position estimates were compared with known positions of fixed tags in both marine (Alaska, USA) and freshwater lake (Ontario, Canada) systems. Accuracy of position estimates ranged from 1.2 m using hull-mounted hydrophones and survey-quality GPS equipment to 23.4 m using towed hydrophones and a navigation-grade GPS receiver. This new tool will facilitate spatially explicit management applications such as aquatic protected area design and essential fish habitat designation by increasing the ability of acoustic telemetry to characterize movement of marine animals at different scales.