Applications of slow-moving autonomous platforms for passive acoustic monitoring and density estimation of marine mammals

• Main Author: Fregosi, Selene
• Other Authors: Klinck, Holger, Mellinger, David K., Heppell, Selina S., Maguire, Doug, Friedlaender, Ari S., Harris, Danielle V., Fisheries and Wildlife, Hatfield Marine Science Center
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Oregon State University
• Subjects: Balaenoptera physalus; Fin whale
• Online Access: https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/kw52jg69r

Advances in mobile autonomous vehicles for oceanographic sensing provide new opportunities for passive acoustic monitoring of marine mammals. Acoustically equipped mobile autonomous platforms, including gliders, deep-water profiling floats, and drifting surface buoys can survey for a variety of marine mammal species over intermediate spatiotemporal scales. Additionally, such mobile platforms may provide an effective tool for population density estimation of marine mammals. This dissertation advances our understanding of how gliders, deep-water floats, and surface drifters can be used for passive acoustic monitoring and density estimation of two cetacean species, fin whales (Balaenoptera physalus), and Cuvier’s beaked whales (Ziphius cavirostris). One glider and two drifting deep-water floats were simultaneously deployed in the vicinity of a deep-water cabled hydrophone array offshore of San Clemente Island, California, USA. The glider was able to follow a pre-defined track while float movement was somewhat unpredictable. Fin whale 20 Hz pulses were recorded by all recorders throughout the two-week deployment and presence at hourly and daily scales were comparable across all recorders. Performance of an automated template detector did not differ by recorder type. However, the glider data contained up to 78% fewer fin whale detections per hour compared to the floats or stationary hydrophones because of increased low-frequency flow noise present during glider descents. Flow noise was related to glider speed through water and dive state. Glider speeds through water of 25 cm/s or less are suggested to minimize flow noise. The cabled hydrophone array was also used to estimate fin whale localizations and tracks concurrently with the glider survey. These tracks were used in a trial-based approach to estimate a detection function for six-minute snapshots containing fin whale 20 Hz pulses. Detection probability was strongly dependent on 40 Hz noise levels (flow noise) recorded on the glider. At the median noise level of ...