Responsible sea management vital for preserving dolphins in Slovenia
Koper, 13 December - The only dolphin species living in the Adriatic Sea today is the common bottlenose dolphin, after a different species became extinct in the sea decades ago. Ana Hace of the Morigenos association for marine mammals says that responsible sea management is needed to prevent the common bottlenose dolphin from experiencing the same fate.
The association has been studying, monitoring and protecting the common bottlenose dolphin in the Slovenian part of the Adriatic Sea since 2002. Most of the research is done in the summer and spring.
The research shows that the common bottlenose dolphin is present in the Slovenian sea throughout the whole year. More than 150 individuals have been identified so far, including 70 to 100 which hang around for the entire year.
"Dolphins also feed, reproduce and take care of their calves here, so we know that this is a very important area for them," Hace said.
The common bottlenose dolphin is a very social animal and is considered a "cosmopolitan species", as it can be found in various seas around the world. It is also one of the most adaptable species of cataceans.
Most the populations in the Mediterranean Sea are small and endangered, which is why it is listed as a protected species.
Photo identification method
The main method used by Morigenos in studying dolphins is photo identification of fins. Dolphins develop marks on their dorsal fins, something like fingerprints in humans, Hace explained.
Based on photo identification, dolphins are named and placed in a photo catalogue of dolphins. This allows researchers to follow individual dolphins and learn about their interactions with other dolphins, about the area they use, and about their fertility and mortality rates.
Marks on their dorsal fins change over time, while calves have no marks on whose basis they could be recognised. The association has thus established that it is also possible to recognise dolphins based on their facial features, which had been previously unknown.
According to Morigenos, the new method cannot replace identification based on dorsal fins, but it can be supplementary. Unlike dorsal fins, dolphin faces are not subjected to much change due to external factors, but can be more reliable in the long run.
The results were presented in a study published at the end of October in the internationally acclaimed journal Marine Mammal Science.
Dolphins are also studied with acoustic monitoring: their sounds are recorded with passive acoustic hydrophones. Slovenian researchers currently use one hydrophone, but they hoping they will be able to expand their network.
Social structure and relatedness
Having conducted an analysis of the social structure of dolphins, the association has established that there are two large groups of dolphins in the Slovenian sea, which inhabit the same area but at different times.
Recent studies have also shown that the populations of the common bottlenose dolphin in the northern Adriatic, including the Slovenian groups, do not mix with the populations around the Croatian islands of Cres and Lošinj. This means that dolphins in the Slovenian sea are not similar to other dolphins in the Adriatic, and they are the most closely related to those living in waters around Greece.
Numerous negative factors affecting dolphins
One of the negative factors affecting dolphins is maritime transport, which produces underwater noise. As hearing is the main sense for dolphins - used for communication, orientation and feeding - noise severely disrupts dolphins and affects their presence.
Pollution is also a strong negative factor. Morigenos researchers have observed dolphins playing with plastics on several occasions. If they accidentally ingest plastics and it gets into their digestive system, they can die. Another danger is chemical pollution with heavy metals, polychlorinated biphenyls and dichlorodiphenyltrichloroethane (DDT), which can affect the immune system and reproduction of dolphins.
A study from 2016 shows that dolphins in the Slovenian sea are quite toxic. Samples of dolphin tissue contained polychlorinated biphenyl (PCB), a toxic and carcinogenic substance used for coatings and sprays which has been banned since the 1980s.
Despite the ban and measures to reduce pollution with PCB, the substance is still widely present in seawater, having numerous toxic effects on apex predators. Based on the studied samples, researchers have found that the concentration of this substance in dolphins is exceptionally highly and can cause disease or even death.
Another species of dolphin lived in the Slovenian sea 40 years ago
Another dolphin species, the short-beaked common dolphin, was present in the Slovenian sea 40 years ago. It has become completely extinct in the Adriatic Sea, even though it was quite widespread in the area. Its extinction in the Adriatic was the result of indiscriminate culling in the previous century and ecosystem changes caused by pollution and excessive fishing.
"Dolphins are crucial in the preservation of a healthy marine ecosystem, and it is vital to make sure that the only extant dolphin species in Slovenia does not suffer the same fate," Hace stressed. "It is important to act responsibly when we are at sea, and to make sure they have a normal and healthy habitat. One of the things individuals can do is to be careful about what they throw into the sea."
Morigenos - the Slovenian Association for Marine Mammals is an independent, non-profit and non-governmental expert organisation. Its main activity is implementing the national project for studying, monitoring and protection of the common bottlenose dolphin in the Slovenian part and the surrounding areas of the northern Adriatic Sea.
The association also conducts scientific research, monitoring, education and awareness-raising campaigns. Its team consists of biologists, veterinarians, geographers, chemists, teachers and other experts, who participate in research projects and organisations in various parts of the world, including in the European Cetacean Society (ECS).
Morigenos is a partner to many Slovenian and international projects, organisations and expert groups and is the only Slovenian organisation with the status of a partner to the Agreement on the Conservation of Cetaceans in the Black Sea, Mediterranean Sea and contiguous Atlantic area (ACCOBAMS).