Differences in sperm whale codas between two waters off Japan: possible geographic separation of vocal clans

Abstract

The sperm whale (Physeter macrocephalus) clan is a social unit that shares a similar repertoire of vocalizations called codas. Coda repertoires and clan structure are well studied in sperm whales of the eastern tropical Pacific, but information is limited in the western North Pacific. We compared sperm whale codas recorded from female and immature sperm whales in 2 areas near Japan, off the Kumano Coast and off the Ogasawara Islands, to determine whether different clans exist in these waters. Repertoires of coda types were different between the 2 areas, and the lengths of codas consisting of the same number of clicks were longer in duration near Kumano than near Ogasawara. Our results suggest that different vocal clans inhabit in these 2 areas. Such clear geographic structure of clans is not known in other waters in the Pacific and distinct environmental features may favor a clan in which members share a specific foraging strategy and coda repertoire, both of which likely are transmitted through social learning.