While cetaceans may look like fish because of their hydrodynamic shape, they are, like humans, placental mammals. Cetaceans display strong intragroup social connections.s.

Standard general classification

The ‘Cetacean’ order is divided into two groups:

toothed cetaceans, or odontocetes (dolphins, sperm whales, porpoises, killer whales, narwhal etc.), which have teeth along their jawbones. Males are generally larger than females. They have a single blowhole and asymmetrical skulls. They are very active hunters, feeding on squid, octopus and fish. Toothed cetaceans form tight-knit groups..

baleen whales, or mysticetes (right whales, Balaenoptera, humpback whales etc.). Mysticetes, also known as ‘baleen whales’ in the term’s broader sense, have baleen plates in their upper jaw. All are big in size and females are generally larger than males. They have two separate, paired blowholes and symmetrical skulls. Apart from grey whales, which feed on the seabed, Mysticetes filter water through their baleen plates, mainly capturing krill, and small shrimp several centimeters in size. It is unusual for this type of cetacean to live in tight-knit groups.

Main characteristics

• Perfectly adapted to life in the water

All cetaceans share a common land-based ancestor, which adapted perfectly to the marine environment as it evolved. The rear legs and tail of this ancestor evolved into fins, with fingers present in the internal skeleton of the pectoral fins, inherited from the species’ land-based ancestors, while the species’ powerful caudal fins are horizontal, unlike in fish sharks. Cetaceans breathe air at the surface through their lungs and nostrils, transformed into blowholes. This form of respiration is not automatic, as it is in humans – it is always a conscious action. It is for this reason that they rest only one half of their brains at a time when sleeping, the other half remaining active.

• Reproduction

Offspring are carried in the female’s womb. After birth, they are fed by their mother’s rich milk for several months. Young cetaceans remain with their mothers for a number of years.

• Senses and echolocation

The toothed cetaceans’ most acute sense is hearing: they use echolocation, a sort of natural sonar, to identify where fellow cetaceans and prey are. High-frequency sonar waves are emitted from a cavity close to the blowhole and are focused and directed by the melon, reflected by the target and received along the lower jaw before being interpreted by the brain. Certain whales, such as humpback whales, are able to communicate over distances of several hundreds of kilometers, producing the repetitive sounds we call ‘whale song’.

• Migration

Most whales migrate over long distances, from the polar regions of both hemispheres, where they consume great quantities of food in summer, to the tropical waters where they reproduce and give birth in winter. In the Mediterranean, fin whales are known to group together to feed in the Sanctuary in summer, but we still do not know if there are particular areas in which they reproduce.

The Sanctuary’s marine mammals

Eight species of marine mammal are found in the Pelagos Sanctuary on a relatively consistent basis. Some species not listed here, such as humpback whales, harbor porpoises and killer whales, are found in the Sanctuary but are sighted only very occasionally (rare or accidental visits). We focus our research on the eight most common species, as well as on the only pinnipeds found in the Mediterranean but not in the Sanctuary: monk seals.

For more information about marine mammals, click here.