Harnessing seafloor telecommunication cables for enhanced marine mammal monitoring: A comparative study of distributed acoustic sensing and hydrophone arrays

Sustainable management of marine industries (e.g., oil and gas, construction, subsea mining, defense, shipping/ports) typically requires baseline assessments and monitoring of marine fauna. In the case of vocal marine fauna such as whales, this is commonly achieved by passive acoustic monitoring using moored acoustic recorders. Recent literature has demonstrated the capability of fiber-optic telecommunications cables (FOC) on the seafloor to detect low-frequency (<100 Hz) sounds of nearby whales by measuring the dynamic strain induced in the cable by sound waves in the ocean [i.e., distributed acoustic sensing (DAS)]. The potential advantage of DAS is the simultaneous sensing along the length of the cable, potentially covering a larger monitoring area and enabling beamforming and thus tracking of sound sources in near or real time. We compared the performance of DAS to that of a conventional hydrophone array in a 2-month field trial off Western Australia. With controlled vessel passes we determined the sensitivity, angular dependency, and detection range of both systems. Migrating pygmy blue and Omura’s whales were recorded and tracked. We discuss the pros and cons of both technologies, and future development needs if existing FOC infrastructure is to be dual-purposed for whale detection for environmental monitoring and management.