Common dolphin – an uncommon visitor in the Gulf of Trieste

Common dolphin (Delphinus delphis) in the Gulf of Trieste. Photo: Tilen Genov, Morigenos

There is an unusual visitor present in the Gulf of Trieste in the past year. It is a short-beaked common dolphin (Delphinus delphis) that Morigenos researchers and biologists from Miramare Marine Protected Area have been monitoring for over a year. It is a species that was once common in the Adriatic, but has become very rare in the last 30 years - it is now considered regionally extinct in the Adriatic Sea.

In June 2010 our colleagues from Miramare informed us about two dolphins of unknown species that were spotted close to the port of Monfalcone several days in a row. We immediately headed out to sea in order to check it out. We found two dolphins, a mother and a calf, inside the port itself. We soon determined that they were short-beaked common dolphins. We photographed the animals for individual identification, assessed their condition and observed their behaviour. The female appeared healthy, but the calf showed signs of poor health. We sent the dorsal fin photographs of the female to our colleagues from Tethys Research Institute in Greece and discovered that she had been encountered there before. This means she travelled at least 1000 km, which is the longest recorded movement of this species, worldwide. We presented this information at one of this year's marine mammal conferences. The mother and calf stayed in the port until February 2011. After this, the calf disappeared and the female moved out of the port soon afterwards. Since then we have been seeing her occasionally in various other locations in the Gulf of Trieste. She looks healthy and often very playful. The most important thing for her now is that people do not harass her or attempt any close contact with her. Wild animals should remain wild. If this dolphin becomes a so called »solitary sociable dolphin« and starts seeking human company, that could in the long term prove to be dangerous not only for her, but also for the people.

The short-beaked common dolphin used to be one of the most widespread and abundant dolphin species in the Mediterranean. Today the Mediterranean population is classified as endangered. Common dolphins have become very rare in the eastern and in several parts of the western Mediterranean. Why this particular female swam all this way and stayed here remains a mystery.