Photos © Morigenos
Photo-identification (or photo-ID) is the central method used in this study. Individual dolphins are recognised by natural markings, such as scars, nicks and notches on dorsal fins (and also other body parts). The dorsal fin is the part of the body that contains most individually distinctive marks by which we can tell dolphins apart. It is also the part of the body that is most commonly visible when a dolphin surfaces to breathe.
These markings are natural and result mainly from encounters between individual dolphins in social interactions. They can also be caused by other marine organisms (such as sharks) and diseases, or encounters with humans (e.g. collisions with boats, propeller cuts, entanglement in fishing gear, etc.). If you want to learn more about how dolphins acquire marks, have a look at: How dolphins acquire marks.
Pigment patterns, shape of the dorsal fin and other peculiarities can also help distinguish individuals. We photograph the animals so that we can carefully examine their marks. We compare new photos to old ones and determine whether we have seen known dolphins or if we have seen new ones. Since 2002 we have photo-identified over 200 dolphins, all of which were given names and included in the photographic identification catalogue.
When a group of dolphins is located, the aim is to get a fin shot of every member in the group. This method is non-invasive as we do not need to touch dolphins or put artificial tags on them. With photo-ID we can get a lot of information on many aspects of dolphin biology and ecology.
With photo-ID we can determine the dolphin population size and monitor their numbers through time. That means we can observe whether the population is increasing, decreasing or being stable. We also use it to assess and study annual survival rates, reproduction rates, distribution, patterns of occurrence, migrations, behaviour, social structure, habitat use and site fidelity of individual dolphins to particular areas. Finally, we can also use photo-ID to observe and study dolphin skin diseases, wound healing process, calves growing up and the personalities of individual dolphins. It also helps us determine the sex of identified dolphins.
By using photo-identification techniques, we have been able to compile the first photographic identification catalogue of dolphins in the Gulf of Trieste. The catalogue now contains more than 200 dolphins that use the Gulf of Trieste and neighbouring waters as their habitat. If you would like to see how the fins of different dolphins from our study area look like, please visit the Photo-ID catalogue.