UC Santa Cruz

Descriptions of underwater vocalizations produced by aquatically mating phocids are available for many species, but are lacking for the endangered Hawaiian monk seal (Neomonachus schauinslandi). We obtained simultaneous year-round audio and video recordings of a captive adult male Hawaiian monk seal to evaluate underwater vocal repertoire and characterize seasonal trends in vocal behavior. A discriminant function analysis based on 17 acoustic parameters revealed that this seal produced at least six discrete underwater vocalizations. Spontaneous aquatic calls were most commonly produced from September through January, during a period coincident with elevated blood testosterone levels and prior to the annual molt. These seasonal patterns in sound production confirm a protracted reproductive season for this tropical species. While limited to a single individual, this first report of underwater sound production expands our understanding of reproductive behavior in Neomonachus schauinslandi, and establishes a foundation for future research and population monitoring efforts using passive acoustics.