Acoustic Profiling of Atlantic Seamounts: Insights towards cost-effective Monitoring of Remote Marine Ecosystems

Seamounts are key biodiversity hotspots for marine ecosystems but highly vulnerable to human impacts, highlighting the urgent need for effective conservation measures. Their remoteness and deep habitats, however, challenge the implementation of the long-term monitoring programs necessary to quantify the protection effect for reliable conservation benchmarks. This study evaluates the potential of passive acoustic monitoring (PAM) combined with ecoacoustic indices as a practical and cost-effective tool for ecological assessment of seamounts. We use this approach to analyze the presence and diversity of fish sounds across four mid-north Atlantic seamounts of contrasting summit depths. Results showed a greater presence and diversity of fish sounds in shallower seamounts, likely reflecting higher habitat complexity and species richness. Acoustic activity also exhibited clear diel patterns, with the occurrence of several sound types showing marked differences between day and night, suggesting temporal variation in fish behaviour and habitat use. Variations in fish sound diversity was ascertained and cross-validated by three ecoacoustic indices: Acoustic Complexity Index (ACI), Entropy (H), and Sound Pressure Level (SPL), and supported by in-situ evidence from underwater visual census at the summits of shallow seamounts. These findings support PAM as a viable and valuable tool for assessing and monitoring fish biodiversity in seamounts, providing essential data at relatively low cost in support of management policies for these fragile ecosystems.