Kategorie: News
Lonely? Playful?
There has been an increase in dolphin attacks on the beaches of the Japanese prefecture of Fukui. By the end of August, 18 people had been injured this year, bringing the total number of ‘human-dolphin incidents’ in the last three years to 29, according to the Coast Guard office in Tsuruga. The injuries range from bite wounds on the hand to broken bones.
Researchers suspect that it is a single male Indo-Pacific bottlenose dolphin (Tursiops aduncus) in all cases, as can be seen from the fin prints in photos and video footage. The journal 'Nature' spoke to Tadamichi Morisaka, a dolphin ecologist at Mie University in Tsu, Japan, about the behavior of dolphins and ways to prevent further attacks.
In the interview (by Nature Mag.), dolphin ecologist Tadamichi Morisaka discusses common dolphin behavior that may explain their sometimes painful encounters with humans.
Why might this dolphin bite swimmers?
Soft biting is a behaviour we often see in male bottlenose dolphins in the wild. They do this to maintain the relationship – in this dolphin's imagination, he may have already established a friendly relationship with people.
We have seen this dolphin randomly show up on a beach, bite when people are around, walk away, and repeat. In my opinion, he is seeking some kind of interaction with people. If it really wanted to attack, it could have charged and bitten with full force. But by dolphin standards, it only gives a gentle nip, so it's probably more of a friendly gesture than an attempt at assault.
How does this behaviour relate to the social structures of bottlenose dolphins in the Indo-Pacific?
Bottlenose dolphins usually live in pods. Males form lifelong partnerships with other males. By living together in pairs, they have better access to females, because two are stronger than one.
These pairs spend many hours playing with each other. This includes behaviours such as chasing each other and rubbing the other dolphin with their pectoral fins – which is considered a sign of affection – and even sexual behaviour, such as pressing their penises together.
Gentle nipping is one of these prosocial behaviours. The dolphin at Fukui is therefore behaving as if it were playing with a human instead of a male mating partner.
Is it unusual for dolphins to be alone?
This is a mystery and an area that requires further research. In the seas around Japan, we occasionally see individual animals leaving the group on their own. Sometimes females leave, and sometimes several individuals leave the pod. The population closest to the beaches of Fukui is found near Noto in Ishikawa Prefecture, but we still need to find out whether the individual responsible for the attacks comes from this population.
How might the attacks change in the future?
We know that there are different phases in the interaction between humans and dolphins. In the beginning, humans and dolphins only share the same space. But the more intense the interactions become, the more the dolphins hurt the humans. At this point, we are in Fukui. When the interaction reaches the next level, dolphins may begin to assert their dominance through aggressive behaviour, such as attacking or mounting humans. We saw this last summer and I was very concerned. They are about 2.5 metres long and weigh around 200 kilograms. So if they were to charge at us at 20-30 kilometres per hour, it would be like being in a road accident. If they were to attack us, it could result in broken bones and internal injuries, among other things.
What has been done to prevent further attacks in Fukui?
The local authorities have set up underwater acoustic devices that play different sounds at random. This is not designed to elicit any particular response in the dolphins, but it is likely to sound strange and annoying. But bottlenose dolphins could get used to it. They are a particularly curious species, and if they find something interesting enough, they will make their way to the beaches regardless of the noise. We have even observed dolphins returning to beaches where these devices are installed.
I would like to develop an early warning system that detects the echolocation they use for navigation. An alarm is triggered as soon as we know that dolphins are approaching. If we are able to get people out of the water in time, the dolphin will probably realise that there is nothing of interest on the beaches and will eventually return to its original environment. Above all, we need to raise awareness of how wild dolphins are.
What other questions do you have about the behaviour of dolphins?
A large part of my work focuses on the acoustic communication of dolphins, but you can discover many strange things when you observe them. Part of my job is to scientifically interpret these behaviours – for example, we have found that they yawn just like us and have wet dreams.
Today, I'm curious about how they perceive the world. They ‘see’ using echolocation, but there are still many unanswered questions about the role of their eyes. In dolphins, each eye moves independently, and they have two stripes in each eyeball that give them high visual acuity. Humans only have one high-acuity spot. What and how can dolphins see with eyes like that? How is visual information combined with echolocation and other acoustic signals? Understanding their perception would help us understand their society, because it forms the basis for their communication - and that shapes their social structures.
Original publication Article Nature (28 Aug 2024)