The Mediterranean monk seal (Monachus monachus)

is the only pinniped found in the Mediterranean Sea. It is a long slender animal with a comparatively small, flat, broad head and upward facing nostrils. They are uniformly black at birth with a distinct white ventral patch unique to each individual. These seals have the shortest hair of any pinniped, changing color from shades of grey, brown to black as they molt and mature, while the ventral patch persists through a life that may span forty years. They feed on fish and mollusks, primarily octopus, up to 3 kg per day. They live alone, or in small groups. Monk seals rest and give birth in secluded coastal caves and inaccessible rocky shorelines. As a result, they are almost impossible to observe in the wild, while attempts to keep them in captivity have failed. Monk seals reach sexual maturity at around four years of age.

Mediterranean monk seal has not been sighted in Adriatic Sea since the middle of the 20th century, and is declared extinct. Her extinction was mainly caused by deliberate killing by fishermen who perceived the species as a competitor for fish. As were dolphins, Mediterranean monk seal was haunted for centuries because of the fishing gear they distroyed. Their extinction was also caused by its habitat loss through development and growing tourism.

There are non - government organisations in Croatia whose aim is to repopulate the Adriatic Sea with this species, and their research is directed toward exploring potential habitats.

The Mediterranean monk seal is protected by law and fine for killing it is 100 000,00 kn.