An unmanned surface vehicle for acoustic telemetry surveys of coastal fishes: range testing, real world performance, and comparison with a stationary tracking array

Eric Reyier^1*Joseph Iafrate²Bonnie Ahr¹Stephanie Watwood²Douglas Scheidt¹Jacob Levenson³Chris Schumann¹

• ¹Herndon Solutions Group, LLC, Kennedy Space Center, United States
• ²Naval Undersea Warfare Center (NUWC), Newport, Rhode Island, United States
• ³Bureau of Ocean Energy Management, United States Department of the Interior, New Orleans, Louisiana, United States

Ocean gliders equipped with acoustic telemetry receivers are a promising approach for studying the movement of marine fishes, but surveys are often brief and lack comparisons with traditional tracking methods. In this study, a Wave Glider unmanned surface vehicle (USV) was deployed on eight multi-week missions to systematically track acoustically tagged animals over the east Florida continental shelf, and to compare its performance to a contemporaneous stationary tracking array. Over a cumulative 190 days and 9600 km travelled, 331 animal encounters with 20 species were recorded, with blacktip shark (Carcharhinus limbatus), blacknose shark (C. acronotus), and red drum (Sciaenops ocellatus) the most frequently detected species. Multiple range test trials with the glider's two acoustic receiver types yielded 50% detection rates at ranges up to 350 m. Boosted regression tree models predicted that the glider's distance from the acoustic tag explained 57-71% of the variability in detection probability, but ocean currents, wave height, and solar irradiance were also influential. When compared to a stationary array comprised of up to 62 acoustic receivers, the Wave Glider detected, on average, 64% of the species and 40% of the tagged animals, but less than 2% of the detections over identical timeframes. Further, animal encounters with the glider lasted only 14 minutes on average, versus 48 minutes for stationary receivers. Nonetheless, the glider performed comparably on a per-receiver basis, yielding similar numbers of encounters, animals, and species. Moreover, it successfully navigated complex bathymetry surrounding offshore sand shoals, relocated several shed tags, and paired encounters with a variety of oceanographic and meteorological measurements. These results confirm that USVs are suitable for systematic coastal fish tracking. While single gliders cannot replace stationary arrays in most situations, they are realistic solutions for relocating animals in remote locations, monitoring dispersal across discrete habitat patches (e.g., reefs, wind turbines), and providing highly localized habitat context.