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Ecology and Behaviour

Breaching and jumping

A jumping bottlenose dolphin. A bottlenose dolphin jumping out of the water. Photo: NASA

Breaching describes a behaviour that involves a whale leaping out of the water in a vertical or nearly vertical direction. When the animals falls back onto the surface of the water, splashes are produced that can be visible from as far as several kilometres away and the accompanying soud may be as loud as a cannon shot. Many whale species have been reported to breach at least occasionaly, but the behaviour is most common and pronounced in humpback, right and sperm whales. Requiring considerable strength, breaching may have several functions, ranging from being a play and muscle excercise for young whales to being a means of display of power during intraspecific competition for mates. Other explanations suggest that it may sometimes help the whales to rid themselves of external parasites, to breathe more easily during a storm, or it may sometimes be part of the animals' foraging behaviour, meant to stun potential prey.

There are other forms of surfacing commonly seen in cetaceans, such as bow-riding or spy-hopping, often seen for example in dolphins. It is not entirely clear yet what the significance of these behaviours may be. Possible explanations range from an energy-efficient mode of transport to orientating above the water surface, getting rid of parasites or simple play.

Ecological Significance of Cetaceans

Ambulocetus attacking a primitive perissodactyl. Ambulocetus attacking a primitive perissodactyl. Painting by Carl Buell (www.olduvaigeorge.com), used with permission.

All cetaceans are carnivorous and therefore are and always have been an important part of marine ecosystems. The Eocene archaeocetes, the oldest cetaceans known to science, started as virtually terrestrial animals, although there is evidence that the most primitive family, the pakicetids, may alsready have foraged in freshwater. Considering the otherwise cursorial adaptations of these animals, it seems possible, however, that the earliest cetacenss chased their prey on land. With their inceasing dependence on water, their hunting techniques also changed. Ambulocetus has been speculated to have ambushed its prey from below the water surface, in a manne similar to that of extant crocodiles. Later archaeocetes, such the protocetids and the basilosaurids had assumed feeding habits similar to that of the extant odontocetes

Whereas the latter primarily prey on fish and invertebrates such as squid (including the giant squid Architeuthis and the colossal squid Mesonychiteuthis), and even other marine mammals, including large whales, mysticetes have developed a different approach. They only feed on small schooling fish and zooplankton, most notably krill. Thanks to recent studies, it has become increasingly clear that large animals and top predators, such as the orcas, play an important role in both terrestrial and marine ecosystems, for example by keeping the numbers of their main prey species down, which otherwise would quickly reproduce and outcompete many other animals in their habitat. The interactions of baleen whales and krill in the Antarctic Ocean in this context are unforyunately poorly understood so far, as is the role of whales as nutrient distributors through their excrements.

A sperm whale devouring a giant squid. A sperm whale devouring a giant squid (Architeuthis. Image by Fritz Geller-Grimm, from a diorama at the American Museum of Natural History; open source licence CC ASA 2.5.

Large whales also play an important role in another ecological context, which was only recognised rather recently. Whale carcasses (also called whale falls) weighing more than 30 tonnes often find their way into deep waters, reaching bathyal or even abyssal depths in excess of 1000 m. In these depths, scavenging is greatly reduced and the carcasses, including the lipid-rich (ca. 60 %) bones, serve as a massive source of organic material for decades, at times housing more than 30000 animals at once. As such, they can support communities of animals independent of sunlight, similar to those found around hydrothermal vents. Though being very episodic and localised events, whale falls are relatively common events and probably served as an evolutionary bridge from continental margin to hydrothermal vent settings, as shown by molecular studies of vent organisms.