Comparing Autonomous Underwater Vehicle (AUV) and vessel-based tracking performance for locating acoustically tagged fish

Autonomous underwater ve hicles (AUV's) are increasingly used to col lect physical, chemical, and biological infor mation in the marine environment. Recent efforts include merging AUV technology with acoustic telemetry to provide information on the distribution and movements of marine fish. We compared surface vessel and AUV tracking capabilities under rigorous condi tions in coastal waters near Juneau, Alaska. Tracking surveys were conducted with a RE MUS 100 AUV equipped with an integrat ed acoustic receiver and hydrophone. The AUV was programmed to navigate along predetermined routes to detect both refer ence transmitters at 20-500 m depths and tagged fish and crabs in situ. Comparable boat surveys were also conducted. Transmit ter depth had a major impact on tracking performance. The AUV was equally effective or better than the boat at detecting refer ence transmitters in shallow water, and sig nificantly better for transmitters at deeper depths. Similar results were observed for tagged animals. Red king crab, Paralithodes camtschaticus, at moderate depths were re corded by both tracking methods, while only the AUV detected Sablefish, Anoplopoma fimbria, at depths exceeding 500 m. Strong currents and deep depths caused problems with AUV navigation, position estimation, and operational performance, but reflect problems encountered by other AUV appli cations that will likely diminish with future advances, enhanced methods, and increased use.