After travelling thousands of kilometres, many humpback whales choose the waters around Réunion island to give birth to their calves. For scientists, this is an opportunity to collect valuable data. This involves surface observation, but also listening to the seabed. The humpback whale is reputed to have the most complex song in the animal kingdom. Réunion is one of the few places in the world where swimming with whales is still permitted, but under strict regulations. In addition to professional divers and operators specialising in on-board observation, independent yachtsmen must also be trained in respectful approaches. IMAGES AND SOUNDBITES