The appearance of a group of sperm whales near Korčula
Today during the morning, we received several reports about the...
In the past few weeks, we have received reports from citizens about sightings of dolphins in the Rijeka Bay and near Rab, which are displaying unusual behaviour, staying in ports and allowing people to approach them. Since the first reports, we have gone to the field several times, photographed and filmed both dolphins, assessed their general condition, and gathered information from the local population about their behaviour and the behaviour of people towards the dolphins.
In both cases, the individuals are short-beaked common dolphins (Delphinus delphis), a species that was considered regionally extinct in the Adriatic Sea since the late 1970s but has been observed again in the past few years. Although common dolphins are a social species that lives in groups of several tens or hundreds of individuals, the dolphins near Rab and Rijeka are solitary common dolphins.
The occurrence of solitary dolphins has been documented in multiple dolphin species worldwide, including the Adriatic Sea, where we have described two cases of solitary striped dolphins (Stenella coeruleoalba) in the Vinodol Channel and Mali Lošinj port, as well as the probably most famous case of a solitary bottlenose dolphin (Tursiops truncatus) named Bobi, who spent several years in the Novigrad and Karin seas.
In general, dolphins are social animals that live in groups with complex relationships and connections. Solitary dolphins are those individuals that separate from the rest of their species and spend most of their time alone without contact with them. We still don’t know why some individuals separate from their groups and become solitary. Possible reasons are numerous – dolphins may be sick or injured, preventing them from keeping up with the group, or they may be expelled from the group. They may become solitary due to trauma caused by the death of other related individuals (e.g., a mother-calf pair) or close social relationships. It is also possible that an individual separates from the group in search of another group, which it cannot find due to the low population numbers, which could be the case with these common dolphins.
It is interesting that regardless of the species, all solitary dolphins show almost identical behavioural patterns that change over time through four described phases. In the first phase, dolphins isolate themselves from other individuals of their species and stay in a smaller area (harbour or bay) where they start showing interest in inanimate objects such as boats or buoys but show no interest in humans. In the second phase, they begin regularly approaching boats or swimming around buoys but still do not allow humans to approach them. In the third phase, they start allowing approach or even physical contact with a small number of people, while finally, in the fourth phase, the dolphin shows no hesitation in interacting with humans and allows or initiates contact with multiple people. If the dolphin reaches the third or fourth phase, it usually becomes a local attraction, attracting a large number of people who want to swim with it.
Intense interaction with humans inevitably poses risks to the well-being of the dolphin as well as the people present nearby. Direct contact with humans can have numerous negative effects on the dolphin: people may disturb it while resting or feeding; swimmers may inappropriately touch the animal, accidentally causing injuries (such as poking fingers into the eyes or blowhole, attempting to ride the animal, pulling its fins, etc.); they may offer inappropriate food or a source of infection, and the dolphin may become accustomed to seeking food from humans, thereby ceasing to hunt for prey. Due to the presence of humans, dolphins are at a higher risk of stranding, entanglement in ropes and fishing gear, or collisions with boats. Moreover, people may intentionally attempt to harm the dolphin, which in several recorded cases has led to the death of the animal.
Considering that it is a wild animal, inappropriate human behaviour can lead the dolphin to display aggressive behaviour. There has been at least one case where a bottlenose dolphin killed a swimmer (in Brazil in 1994) and multiple cases where serious injuries to humans occurred. In most cases, the dolphin’s aggressive behaviour is a reaction to inappropriate behaviour by individuals who tried to ride, hit, or pull its fins, and in one case, even shoved ice cream into the dolphin’s blowhole. Injuries can also occur when the dolphin does not feel threatened but makes sudden movements that can harm a person, even when the dolphin is “playing” or spending time with swimmers.
Therefore, we appeal to everyone in the vicinity not to approach or swim with the dolphin, touch it, or feed it, as it can lead to the animal becoming accustomed to humans, which can have undesirable consequences. In addition to possible aggressive behaviour, there are other dangers in close interactions between solitary dolphins and humans. Dolphins can transmit numerous serious and difficult-to-cure diseases – zoonoses – such as tuberculosis, leptospirosis, etc. Similarly, during close interactions, humans can transmit diseases to the dolphin population, which can cause the death of a large number of animals. Therefore, swimming with them, especially touching them, should definitely be avoided. Also, considering that solitary dolphins lose their natural fear of vessels, they can suffer severe injuries from collisions with boat propellers and die.
According to our knowledge, the common dolphins in the Rijeka Bay and near Rab are in good overall condition. They show no external signs of illness, dive normally, and are not starving, indicating successful hunting. Additionally, there have been no recorded attempts of intentional harm, although there are videos of people swimming and diving with the dolphins. Based on the information available to us, these dolphins are currently not aggressive and do not pose a threat. However, we believe that the behaviuor of people towards them will determine their future.
Dolphins are strictly protected animals, and it is prohibited to disturb them (attempt to feed, swim with, touch, or chase them). Therefore, we urge you to:
You can report your observations of all marine mammals, including solitary common dolphins, through the Marine Ranger mobile application (https://marine-ranger.org), developed as part of the LIFE Delfi project, co-funded by the European Union. Depending on whether you are reporting your observation or want to report harassment, chasing, or the discovery of an injured or entangled animal, the application, based on your location, will offer you the option to contact the relevant authorities (112) and expert organizations (such as the Blue World Institute).
For more information about behaviour near dolphins, please visit our website:
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