The role of touch in marine mammal society: a review and future directions

While social living has many advantages, it also has significant challenges associated with differences in individual needs and abilities. Individuals in social species communicate across sensory modalities to mediate their relationships. Affiliative touch, defined here as nonaggressive physical contact between conspecifics, plays a well-documented role in establishing, affirming and repairing social bonds and facilitating cooperation in some terrestrial taxa. However, the degree to which touch is involved in affiliative behaviours in nonterrestrial species is poorly understood. Marine mammals represent a valuable opportunity for deepening our understanding of the behavioural mechanisms that enable social living through a comparative approach, as they have unique adaptations to different levels of aquatic life and environments and display diverse social structures. Here, we reviewed current trends in research on social touch in marine mammals and evaluated existing evidence for its affiliative functions. Overall, touch was involved in mediating a range of relations, from short interactions with ‘strangers’ to repeated interactions with lifelong associates. We found that the prevalence of tactile interactions outside the mother–infant relationship was generally associated with a species' social structure. But, because of the logistical challenges associated with observing touch in species that spend most of their lives underwater, only a few odontocete species and captive populations dominate the existing literature focused on touch and social interactions. We suggest that leveraging emerging technologies (e.g. uncrewed aerial vehicles (UAVs), animal-borne cameras and thermal cameras), alongside long-term monitoring and study designs that ensure comparability, can expand and deepen our understanding of how animals mediate their social relationships. • Touch is involved in mediating social relationships across terrestrial species. • We review the knowledge and gaps on the social role of touch in marine mammals. • Touch mediates a range of relations and is often associated with social structure. • However, most studies have focused on only a few species or captive populations. • New technologies allow us to study social touch in previously hard-to-access taxa.