Spatial and Temporal Distribution of Vocalising Maile Bearded Seals - Implications for Male Mating Strategies

The bearded seal, Erignathus barbatus, is an ice breeding phocid that mates in the water. The most detailed studies of male behaviour among aquatic-mating phocids have concentrated primarily on temperate breeding harbour seals, Phoca vitulina, where females are dependent on stable substrates, rock or sand, for parturition. In contrast, female bearded seals give birth on ice floes or the edge of fast ice, a highly unstable substrate. In this study, spatial and temporal patterns of male bearded seal vocalisations were studied in Kongsfjorden, Svalbard from April 1999 to the end of May 2000. Males vocalised during a discrete 90-day period from early April to mid July, no calls were heard at any other time of the year during this study. Vocalisations increased in duration towards the middle of the mating season in late May, although no change was seen in inter vocal intervals of individuals. The frequency of occurrence of vocalisations varied significantly with the diel cycle. Vocalisations increased in number from 16:00 hrs onward into the ʹnightʹ, peaking around 04:00 hrs. This peak coincides with the period when most females are in the water. Female bearded seals were found throughout Kongsfjorden. Their distribution at any particular point in time depends on the availability of suitable haul-out sites (i.e. ice conditions), which are highly variable over time spans as short as a few hours. Males vocalised in higher densities around the fjord entrances and may use these ʹgeographical bottlenecksʹ to intercept passing females. We suggest that male distribution may reflect the unpredictable nature of female distribution. Aquatic mating phocids appear to exhibit variations in reproductive strategies, including spatial arrangements of displaying males, which reflect the varying constraints imposed on female movement patterns by their local habitats and ecological requirements.