Culture impacts the distribution and habitat use of sperm whales in the Eastern Caribbean

Abstract

Sperm whales (Physeter macrocephalus) are cetaceans with a worldwide distribution and a complex social structure. Sperm whales are members of cultural groups, called “vocal clans”. Members of a vocal clan have a distinctive suite of socially learned social calls, and do not associate with individuals from other vocal clans. However, whether vocal clan membership has implications beyond the use of a characteristic acoustic repertoire had never been tested in the Caribbean. Via a dedicated survey of sperm whales in the Lesser Antilles, we observed stark differences in vocal clan distributions across relatively small distances (<100km), with little to no overlap between them. These differences in distribution appear to relate to environmental variables with one vocal clan preferring island channels and areas of high eastward current speed and the other preferring canyons with low meridional velocity variance. Such fine-scale habitat partitioning is surprising for a species which is often referred to as an “ocean nomad” and contrasts with Eastern Tropical Pacific clans, which share habitats over much greater scales (we observe a factor of 10 difference between the movements of Eastern Caribbean and Eastern Tropical Pacific sperm whales). We hypothesize that Eastern Caribbean sperm whales are habitat specialists, with vocal clans specializing on the use of certain environmental features and maintaining this specialization through social learning. This not only highlights the need to incorporate culture in the field of conservation management, as different cultural groups have different distributions and habitat use, but also the inherent ties between culture and the environment.