29 Jun 2012

Slovenian and Italian researchers document the longest movement ever recorded in a common dolphin

Morigenos researchers and their Italian colleagues have documented the longest movement ever recorded in the short-beaked common dolphin (Delphinus delphis). A female dolphin swam from Greece to the Gulf of Trieste, travelling more than 1000 km! Even though dolphins are known to be very mobile animals, this is the longest movement ever documented in this species, worldwide.

The study was recently published in the scientific journal Marine Biodiversity Records and involved researchers from Morigenos, Tethys Research Institute, Dolphin Biology & Conservation, and the Miramare marine reserve.

Morigenos researchers mostly study bottlenose dolphins (Tursiops truncatus), the only regular dolphin species in the northern Adriatic. But in 2010, in collaboration with colleagues from Miramare reserve, they recorded a female short-beaked common dolphin with her calf in the Gulf of Trieste. Seeing a common dolphin was surprising in its own right, as this species has virtually disappeared from the Adriatic Sea. But an even greater surprise came when researchers discovered that this dolphin had already been seen in Greek waters in 2008. A method called photo-identification was helpful here – individual dolphins can be identified by natural marks on their dorsal fins. Morigenos researchers photographed the dolphin and sent the photos to their colleagues at Tethys Research Institute, which study common dolphins in Greece. It turned out they already knew this particular dolphin.

Morigenos and Miramare researchers monitored the dolphin since then. She spent most of her time in the port of Monfalcone. The calf disappeared in the beginning of 2011. After that the female was often seen around Trieste until September 2011, when she disappeared as well.

The short-beaked common dolphin has been considered extirpated in the Adriatic Sea in the last 30 years, despite being common in the past. The most likely causes are deliberate killing in the previous century, as well as the ecosystem changes resulting from pollution and overfishing. The common dolphin has also became rare in other parts of the Mediterranean, except in the Alboran Sea. The nearest population to the Adriatic Sea is found in the Ionian Sea off the coasts of Greece.

With a single case being reported here, these findings about the long-distance movement cannot necessarily be generalised to the entire species. Unfortunately, this also does not mean the common dolphin is returning to the Adriatic. Still, this study shows the effectiveness of photo-identification in common dolphin research, and shows that international collaboration is vital to the study, monitoring and conservation of mobile marine species.

The scientific paper can be viewed here:

Genov, T., Bearzi, G., Bonizzoni, S. & Tempesta, M. 2012. Long-distance movement of a lone short-beaked common dolphin Delphinus delphis in the central Mediterranean Sea. Marine Biodiversity Records, 5 , e9 doi:10.1017/S1755267211001163.

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