The bottom contact behaviour observed in cetaceans is mainly related to cleaning or feeding functions. This behaviour was already related to feeding strategy for bottlenose in Bahamas (Rossbach and Herzing 1997), for estuarine dolphins in Brazil (Rossi-Santos and Wedekin 2006) and humpback whales in North Atlantic (Hain et al. 1995). However, the feeding hypothesis is less probable due to the rare records of feeding by humpback whales in Brazilian waters (Alves et al. 2009), considered only as a breeding ground (Zerbini et al. 2004).
On the other hand, there are records of cetaceans rubbing their skin on sand, mud, pebble and limestone substrate near shore, a behaviour associated with moult (Smith et al. 1992) and hygienic functions (Dudzinski 1998). According to Smith et al. (1992), the seasonal variation of water temperature accelerates the turnover of superficial layers in belugas, where the whales rub themselves on the bottom, a process that appears to help the moult. This process is so far unknown in other cetaceans, but might have happened in the humpback whale here reported, since it probably had just migrated from the cold Antarctic waters to the warm tropical Trindade coast. Moreover, the flipper slap behaviour initially observed for this forth individual could be also related to the cleaning/moult process as well. This behaviour is commonly considered a form of communication, in order to maintain acoustic contact between humpback whales (Herman and Tavolga 1980). However, the expected low numbers of whales around Trindade in that period decreases the possibility of communication purposes. Despite such uncertain reason of the behaviour, this novel record comes to increase the behavioural repertoire for the humpback whales in Brazilian waters and may represent an additional cleaning strategy.