Dear colleagues, On behalf of my coauthors, I am excited to share our recent open-access publication in Royal Society Open Science. Parnell K, Smith C, Diaz A, Fertitta K, Thompson P, Patton PT, Charrier I, Robinson SJ, Pacini A, Bejder L. 2025 Underwater sound production of free-ranging Hawaiian monk seals. R. Soc. Open Sci. 12: 250987. https://doi.org/10.1098/rsos.250987 Abstract: Hawaiian monk seals (HMS; *Neomonachus schauinslandi*) are endemic and endangered with a population of ~1,600 individuals. While research has provided extensive information on HMS biology, movements, and population ecology, its underwater vocal behavior remains largely undocumented, with previous descriptions limited to two individuals in human-care. To broaden our understanding of sound production in free-ranging seals, we deployed passive acoustic recorders at five sites across the Hawaiian Archipelago. From

4,500 hours of recordings, we manually detected and classified >23,000 underwater vocalizations. A discriminant function analysis of 10 call types yielded an average correct classification rate of 63%. We identified 25 call types, including five published elemental calls and 20 novel calls. Nineteen of the novel call types were combinational calls—an undocumented communication strategy in pinnipeds. The novel *Whine*, captured via biologging tag- and citizen-scientist videos, provided a rare example of context-specific call use in pinnipeds. Vocalizations were low-frequency (<1 kHz), short-medium duration (<7 sec), with 66% occurring in bouts. Calls were detected throughout the day at three of five sites, with peaks at night and late afternoon. These findings establish a baseline for HMS vocal behavior and emphasize the importance of acoustic communication in future research and conservation efforts.

Please reach out if you have any questions: keparnel@hawaii.edu Cheers, Kirby Parnell -- Kirby Parnell, M.Sc. (Citizen, Cherokee Nation/ᏣᎳᎩᎯ ᎠᏰᎵ; she/her) Ph.D. Candidate, Marine Biology Graduate Program Marine Mammal Research Program University of Hawaiʻi Mānoa *https://www.mmrphawaii.org/kirbyparnell <https://www.mmrphawaii.org/kirbyparnell>*