Underwater vocalizations and vocal activity of captive harp seals (Pagophilus groenlandicus)

Pinnipeds are ecologically and socially diverse, attributes that are reflected in their systems of communication. The purpose of this investigation was to document the vocal repertoire and annual cycle of vocal activity in the harp seal, a species that communicates mainly underwater, but whose social and communicative systems are poorly known.;The study's main objectives were to describe the vocal repertoire of captive harp seals through a complete annual cycle and to document annual, seasonal and diel trends in vocal activity. Plasma testosterone in males before, during and after the breeding season were also analyzed to document relationships of testosterone concentration to vocal activity.;The repertoire comprised 18 vocal classes, eight of which have not been described previously. Vocal activity varied seasonally and with time of day. Calls of low frequency (;Levels of plasma testosterone were investigated in four captive harp seals of different ages. Concentrations varied from a minimum of ca. 0.01 ng/ml in April and May to a maximum of 9.4 ng/ml in March. Peaks in concentration occurred at the time when testes are largest in mature wild males, which is several weeks before wild females enter oestrus. Also, peaks in concentration were correlated with high rates of vocalisation. Peak levels of testosterone were lowest in the young and socially subordinate seals.