Hawaiian monk seals (HMS; Neomonachus schauinslandi) are among the most endangered and evolutionarily distinct phocid species. Until recently, their underwater acoustic behavior was poorly understood. Since 2017, our research efforts have aimed to characterize HMS sound production in both managed care and wild contexts. Initial studies documented the first underwater vocalizations from two mature male seals in human care, revealing six low-frequency (1 kHz) call types produced seasonally. Building on this, over 4500 h of passive acoustic recordings from five sites across the Hawaiian Archipelago revealed an expanded repertoire of 27 call types from free-ranging seals. Using paired video–audio data from biologging tags and citizen-science videos, vocalizations were associated with five behavioral states (swimming, resting, social, foraging, and other). A novel ForagingCall was identified, providing a rare example of context-specific call use in pinnipeds, along with evidence of non-social vocal production by females. Complementary soundscape analyses within HMS critical habitats quantified broadband noise levels (range: 108–123 dB re 1 μPa) and revealed diel patterns driven by biological and anthropogenic sources. This research has informed a deep-learning-based detector and classifier, providing tools for long-term passive acoustic monitoring and advancing understanding of acoustic communication in HMS behavioral ecology and conservation.
Parnell et al. (Wed,) studied this question.