Vocal repertoires and insights into social structure of sperm whales (Physeter macrocephalus) in Mauritius, southwestern Indian Ocean

Abstract

Sperm whales communicate using codas (stereotyped click sequences). Females and juveniles live in long-term social units, and units with similar coda repertoires share vocal clan membership. Vocal clans exhibit culturally defined differences in their multilevel social structure. Here, we aimed to identify different social units among sperm whales in Mauritius in the southwestern Indian Ocean, and to describe and compare their coda repertoires to investigate the presence of different vocal clans. We conducted six boat-based surveys between 2008 and 2013, during which 101 different individuals were photo-identified. Analysis of associations between 22 resighted individuals divided them into four candidate social units, but a lack of resightings impedes solid delineation of social units. Based on number and rhythm of clicks, at least 24 discrete coda types were detected among 4,767 analyzed codas using two different classification methods. Comparison of coda repertoires recorded from seven sperm whale groupings revealed the possible existence of two sympatric vocal clans, but the size differences of recorded repertoires warrant caution of interpretation. To further evaluate social structuring and the presence of different vocal clans in this region, future surveys should aim at obtaining long-term sighting and acoustic data, and cover a more extensive area.