Acoustic Baseline Monitoring of Marine Mammals Offshore West Africa: Using an Autonomous Surface Vessel

A marine mammal baseline monitoring program was initiated offshore São Tomé and Príncipe in 2018–2019. An AutoNaut autonomous or uncrewed surface vessel (USV) was deployed by Seiche Ltd. The aim of this study was to identify occurrence and distribution of marine mammals as part of a wider baseline data collection program, which also included the use of fixed location acoustic recorders, moored to the seabed for monitoring at specific locations. The USV provided an opportunity to collect data over an area of 6840 km2 between the two islands and off the east coast of São Tomé. The minimal physical footprint of the USV equipment shipment, deployment, and autonomous or remote control provided substantial cost and safety advantages compared to conventional vessel-based towed passive acoustic monitoring (PAM) methods—which would otherwise have involved logistical resources and challenges. Assembly, launch, and recovery activities were based at a location with access to a small sandy beach. A two-person team with local support mobilized, serviced, and demobilized the USV. The mobility and unobtrusive nature of the AutoNaut platform enabled successful acquisition of PAM data over a wide area. Vocalizations of humpback whales, sperm whales, beaked whales, and delphinid species were recorded throughout the survey.