Diel and seasonal patterns of underwater sounds by Weddell seals, leopard seals, and killer whales in the Antarctic: When it's adaptive to be quiet

Automated underwater recordings of the Weddell seal (Leptonychotes weddellii) were taken during the 1977/1978 austral breeding season in McMurdo Sound, Antarctica. The recordings were taken continuously for 2.5 minute periods once per hour from October 1977 to January 1978 at two Weddell seal breeding colonies, Hutton Cliffs and South Turtle Rock Crack. During the height of the breeding season Weddell seals reside in fastice areas free of predators and produce up to 75 underwater calls per minute associated with territorial defense and mate attraction.;These recordings also provided data on underwater vocalizations from nearby predators, specifically the leopard seal (Hydrurga leptonyx ) and the killer whale (Orcinus orca). In early December, typical winter storms breakup the fast ice habitat and predators are able to move close to the Weddell seal breeding colonies. Killer whales prey on Weddell seal adults and pups. Leopard seals prey on Weddell seals pups, especially towards the end of the breeding seasons when newly weaned pups start to disperse.;Both predators increased their underwater vocalization rates when they were nearby the two Weddell seal breeding colonies. In contrast, Weddell seals dramatically decreased their underwater vocalizations compared to during the breeding season, which may be an anti-predation strategy to avoid detection by predators.