Selective self-rubbing behaviour

in Indo-Pacific bottlenose dolphins off Hurghada, Northern Red Sea, Egypt.

Hypotheses for the functional role of self-rubbing or object rubbing in odontocetes include hygiene (e.g. ectoparasite removal), sensual pleasure, play and socialisation. Self-rubbing has only been described in a few odontocetes, which rub themselves on substrates such as sand, pebble stones, sea grass or rocks. However, rubbing on corals has not been described yet, likely due to the constraints of boat-based observations and/or the lack of corals at the various study sites, or even to cultural differences of populations. Around Hurghada (Northern Egyptian Red Sea), Indo-Pacific bottlenose dolphins (Tursiops aduncus) are systematically studied through a unique combination of above and underwater surveys. Event sampling from underwater video recordings conducted while scuba diving showed that dolphins rub their bodies into sand, seagrass and different coral species.

Dolphins appear to be selectively matching certain body parts to specific corals. While the whole body is rubbed into sand, seagrass and gorgonians (Rumphella aggregata), dolphins select leather corals (Sarcophyton sp.) and sponges (Callyspongia sp.) to rub mostly their head region, ventral side and fluke. Particular hard corals (Favia sp.) are only used for rubbing the edges of pectoral fins. This study is the first to describe this extent of selectivity in self-rubbing in any cetacean, in terms of both body parts and the specific coral species involved. It indicates that dolphins in their natural environment may have an elementary need for self-rubbing, which in turn has implications for the welfare of cetaceans in captivity.