A ‘‘sexually frustrated’’ dolphin has been named as the perpetrator of an attack on a Japanese man, with experts believing that it may be responsible for at least 20 other attacks on swimmers over the past three summers.

The man, who was at the beach with his family, said the dolphin swam up to him without provocation before attacking him.

“It kept attacking me and I genuinely believed that I was going to die,” he said.

“I was most worried that I was going to be dragged under the water and further out to sea.”

The man was rescued by a nearby surfer, before being taken to hospital where he received stitches for bite wounds.

Experts say the dolphin is potentially responsible for 15 attacks this summer, five incidents last year and one in 2022.

“Just as in humans and other social animals, hormonal fluctuations, sexual frustration or the desire to dominate might drive the dolphin to injuring the people it interacts with,” Dr Simon Allen, a biologist and dolphin researcher, told the BBC.

“Since they are such powerful animals, this can lead to serious injury in humans.”

Why do dolphins attack people?

Dolphins aren’t normally aggressive to people and certainly don’t eat us. But they have been known to attack swimmers at times.

According to American Oceans, a conservation group that teaches about marine species, dolphins can attack for a variety of reasons, including because they may perceive humans as a threat.

“In some cases, dolphins may also attack humans as a form of amusement, which can be dangerous due to their size and strength,” it said on its website.

“Dolphin mothers are known to be fiercely protective of their babies and may attack humans if they feel that their offspring are in danger.”

British researchers have found that swimming close to bottlenose dolphins and touching them can create stress in the aquatic animal, and can prevent them from resting, feeding or looking after their young.

Dolphin Research Australia, a marine conservation organisation, said regulations in Australia banned swimmers from getting closer than 30 metres from dolphins in the wild.

“Frequent encounters with vessels can cause significant changes and disruption to the behaviour and acoustic communication of dolphins,” the organisation said.

“The disturbances can accumulate and have long-term consequences such as reductions in reproductive success and displacement from core habitat.”

Another reason dolphins can become aggressive is if they are fed regularly by humans, which can lead to begging, stealing bait and catch from lines.

“Dolphins teach each other,” Dolphin Research Australia said.

“The young of mothers who rely on hand feeding never learn how to naturally forage, care for or protect their young.”

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A research study into dolphin behaviours found they can teach hunting behaviours across families and social groups, after 19 dolphins in Shark Bay, Western Australia, were shown to share the same method of hunting shelled sea creatures.

Other attacks

It followed a series of attacks in Japan’s Fukui prefecture during July 2023, when a man in his 60s suffered broken ribs and bites to his hands after a dolphin rammed him a few metres off Suishohama beach in the town of Mihama, the BBC reported.

Another man, in his 40s, had his arms bitten in a separate incident on the same busy beach the same morning.

Two more people were injured by the mammals later in the day.

Although it’s out of character for dolphins to target humans, it’s not unheard of. In fact, it was the second year in a row that dolphins had hurt beachgoers in the area.

In the northern summer of 2022, at least six people were bitten by a single animal – thought to be an Indo-Pacific bottlenose dolphin.

The most seriously hurt needed 14 stitches to close a gash at the base of their thumb.

Authorities warned swimmers against approaching or touching the mammals, and put up signs on the beach. They’ve even installed ultrasound transmitters in an attempt to ward off rogue dolphins.

Last year, swimmers at a beach in Fukui City in Japan were told not to swim in the water after a rampaging dolphin attacked multiple people, resulting in two swimmers being taken to hospital, according to Newsweek.

There are dozens of incidents recorded each year, but there are no known deaths because of a dolphin attack.