Photographers have captured two male humpback whales having sex, in what experts say is the first time the species has been documented exhibiting sexual activity of any kind.

The social behavior of humpback whales has been studied and chronicled for decades. But in a study released this week in the journal Marine Mammal Science, the authors said they’ve produced the first photographs of this species having penetrative sex. 

The report’s three authors are marine biologist Stephanie Stack and the two photographers who captured the encounter, Lyle Krannichfeld and Brandi Romano, in waters west of the Hawaiian island of Maui in January 2022.

“We realized pretty quickly that there was a scientific significance to it,” Krannichfeld, 44, said. “Even if there were no articles published or nothing ever came of it, we knew that it was important to the scientific community and those who were studying the whales just because of the unique behavior.”

The encounter occurred between one male whale who appeared unhealthy or injured and a strong and healthy male whale, the report stated. The whale that received penetration was visibly emaciated and covered in whale lice that can proliferate on humpback whales that have lost mobility, the report said. 

The authors suggested the emaciated whale may have approached the photographers’ friend’s boat to seek cover from the other whale. Krannichfeld stressed that he and his friends did not approach the whales by boat or get out and swim with them once they approached, both of which are illegal.

After circling the boat and attempting to swim away from the healthier whale, the emaciated whale eventually succumbed, the report said. The healthier whale then held the other whale in place with its pectoral fins and began to penetrate the other whale.