During the spring breeding season, male bearded seals produce underwater vocalisations built around a long descending trill, often ending in a low moan. Individual songs can run for a minute or more, and the call carries far under ice, having been detected on hydrophones many kilometres from the singer.
The songs appear to serve territorial and mate-attraction functions. Males repeat structured song types with individually consistent features, which has allowed researchers to distinguish individuals acoustically and to use passive acoustic monitoring to map bearded seal presence across the Arctic without ever seeing an animal. That is valuable in a region where visual survey is expensive and weather-limited.
What acoustic data cannot yet deliver is abundance. Detecting a singing male tells you a male is present and vocal, not how many seals are in the area or what the sex ratio is, and calling rates vary with season and ice conditions. Converting detection rates into population estimates remains an unsolved problem.