Bearded seal (Erignathus barbatus) vocalizations across seasons and habitat types in Svalbard, Norway

摘要

Male bearded seals (Erignathus barbatus) use vocal displays to attract females and to compete with other males during the mating season. This makes it possible to monitor breeding populations of this species using passive acoustic monitoring (PAM). This study analysed year-round acoustic data records from AURAL instruments in Svalbard (Norway) to investigate seasonal variation in the acoustic presence of male bearded seals and the phenology of different call types (long, step and sweep trills) at three sites representing a variety of habitats with varied ice conditions. Male bearded seals vocalized for an extended period at a drift-ice site (Atwain; January-July) north of Spitsbergen, while the vocal season was shorter at a High Arctic land-fast-ice site (Rijpfjorden; February-June) and shorter yet again at a west-coast site that has undergone dramatic reductions in sea ice cover over the last 1.5 decades (Kongsfjorden; April-June). Generalized Additive Models showed marked seasonal segregation in the use of different trill types at Atwain, where call rates reached 400 per h, with long trills being the most numerous call type. Modest segregation of trill types was seen at Rijpfjorden, where call rates reached 300 per h, and no segregation 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 peak vocal activity (May-June) occurred after the sea ice disappeared. Ongoing climate warming and sea ice reductions will likely increase the incidence of such mismatches and reduce breeding habitat for bearded seals.