Aquatic vocalization activity indicates the timing of the mating season of Saimaa ringed seals

Underwater vocalization is widely documented in phocids. In aquatic mating species, vocalization is typically associated with breeding, including intraspecific agonistic behavior and mate attraction. Ringed seal (Pusa hispida) produces a diverse range of aquatic vocalizations. However, the connection between these vocalizations and reproductive behavior is unclear. The Saimaa ringed seal (P.h.saimensis) also produces a variety of underwater vocalizations, with knocking calls especially suggested to be connected to the breeding season. In this study, we used four passive hydrophones during two successive winters, deployed in the breeding habitat of ringed seals in Lake Saimaa, to further explore vocalization behavior. A total of 13,197 vocalization events were identified in the recordings. Only a single vocalization type was recorded and classified as quick knocks. We identified a strong temporal pattern, with vocal activity peaking in April. This peak coincides with the end of the nursing period when mating is assumed to occur. Based on this and earlier studies, we propose that this specific call type is emitted for mate attraction or defense of underwater mating territory. This study pinpoints the timing of the mating season of Saimaa, the ringed seal and provides further insight into the behavior of this endangered subspecies.