Beaked whale bioacoustics: knowledge gaps, vulnerability, and conservation imperatives in the Anthropocene

Marine mammals provide important ecosystem services but are highly vulnerable to anthropogenic noise. Beaked whales (Ziphiidae), among the deepest-diving and least understood marine mammals, remain particularly enigmatic due to their elusive behaviour and limited surface time. Although scientific research efforts have been organized around beaked whales since the 1970s, knowledge of their bioacoustics and responses to anthropogenic sound remains incomplete. Here, we synthesize over two decades of bioacoustic studies to reveal critical gaps in understanding their vulnerability to anthropogenic noise and propose urgent conservation measures in the Anthropocene. Beaked whales produce species-specific frequency-modulated echolocation clicks, with inverse scaling of biosonar frequency relative to body mass, showing evolutionary convergence in biosonar traits. Their specialized auditory anatomy, including unique acoustic pathways and waveguides, supports sensitivity to high-frequency sound, with peak hearing sensitivity between 22 and 64 kHz matching their echolocation spectra. Anthropogenic noise, especially naval sonar, can cause severe behavioural disruption, including foraging cessation, avoidance, abnormal diving, and potentially mass strandings linked to decompression sickness. Species-specific sensitivity thresholds indicate that current noise criteria may not adequately protect beaked whales. Urgent evidence-based conservation measures include expanding global acoustic monitoring, refining hearing assessments, quantifying population-level noise impacts, implementing stricter sonar regulations, and establishing acoustic refugia to safeguard these vulnerable cetaceans in increasingly industrialized oceans.