Dolphin Who Keeps Attacking Swimmers May Be Motivated by Sex, Experts Say

"To me, he's seeking some kind of interaction with people."

Cetacean Blues

You've heard of yacht-sinking orcas (which are still at it, by the way). But there's another menace terrorizing humans at sea: a lonely, playful, and possibly horny dolphin.

The cetacean, a male Indo-Pacific bottlenose, is being blamed for a recent series of over a dozen attacks on swimmers at a beach town in Japan, inflicting injuries ranging from bites to broken bones.

The attacks have been going on for three years now, reoccurring each summer in the waters off Tsuruga, and several other towns, in Fukui Prefecture.

This most recent spell, according to NBC News, has seen 18 dolphin attack victims since July 21, for a total of nearly 50 since 2022.

Guys Being Dudes

Researchers have determined that the culprit is the same male based on fin markings shown in footage of the attacks.

According to Tadamichi Morisaka at Mie University's Cetacean Research Center, the "gentle biting" is common among male bottlenose dolphins as a way of maintaining friendships.

"To me, he's seeking some kind of interaction with people," Morisaka told Nature. "If he really wanted to attack, he could have come tackling at full force and chomped down. But he's keeping the biting gentle for dolphin standards, so it's probably a friendly gesture rather than a full-on attempt to attack."

These male dolphins hang out in pairs and can get quite intimate to show their affection to each other while playing.

"This includes behaviors like chasing each other and rubbing the other dolphin with their pectoral fins — which is thought to signal fondness — and even sexual behaviors, such as pressing their penises against each other," Morisaka said.

Simon Allen at the Shark Bay Dolphin Research project told the BBC that "hormonal fluctuations, sexual frustration or the desire to dominate might drive the dolphin to injuring the people it interacts with" — so it's possible there's a carnal bent to its antics, too.

Friends to Enemies

The dolphin's solitude, however, is trickier to explain. Why dolphins leave their pods in general — and whether this behavior could be considered "unusual" — is a mystery, Morisaka said.

While this dolphin may just be trying to be friendly for now, there's also potential for things to turn genuinely hostile. As Morisaka explains, human-dolphin interactions progress in phases, starting from "just sharing the same space," which we're already well past.

"If the interaction progresses to the next stage, dolphins can start asserting dominance through aggressive behaviors such as tackling or mounting people," he told Nature. "We saw a bit of this last summer, so I was very concerned."

The most recent attack took place on August 20, when a 50-something-year-old man was bitten on both hands while trying to shoo the dolphin away, according to NBC. And from what it sounds like, this probably won't be the last we hear from this persistent sea creature.

More on marine life: Watch Thousands of Sleeping Sharks Form a "Carpet" on the Ocean Floor