Bearded seal vocalisations across seasons and habitat types in Svalbard (Norway)

Abstract

Male bearded seals use vocal displays to attract females and compete with other males during the mating period, making it possible to monitor breeding populations using passive acoustic monitoring (PAM). This study analysed year-round acoustic data from underwater recorders at three sites with different environmental conditions in Svalbard (Norway). Male bearded seals vocalised for an extended period at the drift-ice site (Atwain; January-July), while the vocal season was shorter at the fast-ice site (Rijpfjorden; February-June) and shortest at a site where a dramatic reduction in sea ice cover has occurred (Kongsfjorden; April-June). Generalised Additive Models showed marked seasonal segregation in the use of different trill call types at Atwain where call rates reached 400 per h, with long trills dominating during the study period over step and sweep trills. Modest seasonal segregation was seen at Rijpfjorden, where call rates reached 300 per h and no seasonal segregation in trill types occurred in Kongsfjorden (peak call rate 80 per h). Sea ice cover was available throughout the vocal season at Atwain and Rijpfjorden, while at Kongsfjorden there was a mismatch between the peak in vocal activity (May-June) and the time when ice was present (until April). Some call types might be preferentially used if their properties make them more suitable for attracting females in certain environments. This study provided novel information about vocalising male bearded seals at sites with different environmental conditions in Svalbard and confirmed that PAM is a useful tool for studying this species in a warming Arctic.