The Mediterranean monk seal (Monachus monachus) is one of the most endangered mammalian species in the world. It has a highly fragmented distribution including the temperate and subtropical waters of the Mediterranean Sea and the eastern Atlantic Ocean. It is estimated that species is currently represented with around 600 individuals grouped into three geographically isolated subpopulations – Eastern Mediterranean (Greece, Cyprus, Turkey), Western coast of Africa and Madeira archipelago. Increasing human pressure and deterioration of their suitable habitats has led to a change in the social behaviour of the species. Once a gregarious species forming colonies they are now more often found as solitary individuals or present in small groups. Although generally described as a sedentary species with individuals having limited home ranges they are capable of travelling great distances within short periods of time.
The historic distribution of the Mediterranean monk seal used to include the Adriatic Sea. In fact, the first description of the species is based on an individual caught in 1777 near the island of Cres, Croatia. In the 17th and 18th century the presence of the Mediterranean monk seal was reported along the entire eastern Adriatic coastline, from Istria to Montenegro while most of the reports on caught individuals from the 19th century came from the Kvarner (north Adriatic Sea) and Dalmatia regions (central and south Adriatic Sea). A first form of protection of this species came in 20th century when a reduction in the presence of the monk seal in the central and south Adriatic Sea has been reported (island of Biševo, Svetac, Sušac, Vis, Hvar, Brač, Palagruža, Lastovo, Korčula, Mljet, Pelješac and near Dubrovnik). Based on the IUCN Red Book of Mammals for Croatia this species is currently listed as regionally extinct in the Adriatic Sea.
In June 2005, the first confirmed report of the reoccurrence of the Mediterranean monk seal in the Adriatic Sea was made when the species was positively identified based on photo documentation obtained near the island of Silba, northern Adriatic. Since then, continuous presence of single female Mediterranean monk seal along the north eastern Adriatic coastline has been documented. Analysis of the photographic material collected during the observations has verified the continuous presence of the same individual around the Istrian Peninsula, the Kvarner and the Kvarnerić Channel. This individual died of natural causes in August 2014 and since then rare new sporadic observations of the monk seal have been reported in the Adriatic Sea. Due to the lack of photographic material, the interpretation of such events can only be hypothesised. It is likely that vagrant individuals originating from the nearby colonies of the Ionian and Aegean Seas enter the Adriatic Sea, staying only for a limited time before returning towards the rest of the Mediterranean. Similar occurrences of Mediterranean monk seals have also been described in other areas where this species is considered geographically extinct.