Abstract

Unlike the large number of species of true dolphins, there are only seven porpoise or phocoenid species, inhabiting different habitats and climate zones. They range from ice-covered water in the Arctic to the subantarctic islands through tropic waters and even in freshwater river systems. Some species like the harbour porpoise are widely distributed in both the Atlantic and the Pacific, while the vaquita has the most restricted range of any cetacean and only lives in a small northern part of the Gulf of California, or Sea of Cortez, in northwestern Mexico, where it is now close to extinction due to illegal fishery. Little is known about porpoise species compared to many dolphin species as they generally have an elusive behavior or live away from human attention. However, the finless porpoise and the harbour porpoise have been kept in captivity for many years with success, contributing to knowledge on social interactions, breeding behavior, and sensory physiology. In recent years, a growing number of studies of wild porpoises using advanced electronic tagging devices have greatly improved our knowledge of movements, acoustic behavior, feeding ecology, and reactions to noise disturbance. We now know that harbour porpoises are widely distributed over most of the deep north Atlantic during winter and therefore not only a coastal species as previously thought. We also see very similar echolocation behavior between the finless and the harbour porpoises, showing an almost constant hunt for food, but also inactive periods that may be interpreted as sleeping. Ship noise has been shown to have a significant effect on feeding buzzes, and loud sounds may cause pauses in echolocation and fast movements away from the sound source, which again may result in bycatch and in rare cases mass stranding. Tagging data have also shown that harbour porpoises are much more social than previously thought and have acoustic contact to conspecifics up to 58% of the time between mother and calf and 36% between animals tagged alone. With these new findings, our growing understanding of porpoise behavior has opened a window to their elusive lives that could help improve management and conservation decisions.