Southern Resident Killer Whale calls in Puget Sound analyzed by hydrophone for feasibility with distributed acoustic sensing

Pushing distributed acoustic sensing (DAS) methods from typical seismic frequency ranges into higher frequencies (500 Hz to 1 kHz) will greatly advance the tools available for broad spatial scales of marine mammal monitoring. Recordings from an Orcasound hydrophone stationed near a pre-existing fiber optic cable in Puget Sound were analyzed throughout the fall of 2024 for Southern Resident Killer Whale (SRKW) calls. Simultaneously, the cable was illuminated and interrogated to gather DAS data. The acoustic calls were corroborated with citizen science data of visual sightings to filter the calls spatially relevant to the DAS system. The hydrophone data was processed in a method designed to mimic the DAS system specifications. Determining the exact power spectra of each call for specific frequencies (0–1 kHz) provides a much stronger framework for identifying killer whale calls on pre-existing cables with unknown armoring or positioning. This study allows for exploration and expansion of DAS into higher frequencies to monitor SRKW and other marine mammals with limited fieldwork required compared to studies that may require laying a specialized cable. Ultimately, using hydrophone data will accelerate the movement of DAS into the marine mammal observation realm for species with higher-frequency vocalizations. [Work supported by Orcasound.]