4 people were wounded in a spree of rare dolphin attacks off a beach in Japan, reports say

• Dolphins wounded four people in attacks off the Japanese coast this weekend, according to local media.
• The latest attacks happened off Suishohama beach in the town of Mihama, Fukui prefecture.
• Experts say dolphins can become aggressive, but attacks are rare.

Dolphins have wounded four people in a spate of attacks off the coast of Japan, according to reports in the local media.

Japanese daily Asahi Shinbun, citing local police, said a dolphin injured a man in his 60s who was taking an early morning swim Sunday off the popular Suishohama beach in Mihama, Fukui Prefecture.

The man was swimming five meters offshore with a friend when the dolphin rammed into him, according to the Tsuruga Police Station.

According to the report, the man suffered broken ribs and bites to the hand.

That same morning, a dolphin bit another man in his 40s on his arm, the report said. It is not clear if it was the same dolphin on both occasions.

The BBC reported that two other people were attacked in the same location that day, but it did not have details on those incidents.

Local authorities say they have so far recorded six dolphin attacks on humans this year, Asahi Shinbun reported.

And last year authorities installed ultrasonic transmitters in Koshino Beach, Fukui Prefecture, after a series of dolphin attacks, according to reports. Local authorities said that beach-goers sometimes attempted to approach and pet the dolphins, Insider reported at the time.

Dolphins are highly intelligent mammals, generally known for their friendly behavior towards humans.

But American Oceans, a US conservation group, says dolphins can become aggressive if they believe they are in danger or their territory is threatened.

"Dolphins are wild animals and may see humans as a potential threat to their territory or prey," it said, adding: "In some cases, dolphins may also attack humans as a form of play or amusement, which can be dangerous due to their size and strength."

It's unclear from the reports what kind of dolphin is believed to be responsible for these recent attacks.