The footage of the mating whales marks the first time that sexual acts of humpback whales have been observed at all. Furthermore, it is rare for researchers to have observed the penis of a male humpback whale: the genitalia, over a meter long, barely protrudes, only during urination and mating.

One of the whales held the other in place with its fins, allowing it to penetrate. According to the researchers, the penetrated whale appeared much weaker. It was described as "emaciated" and covered in whale lice.

Stephanie Stack, a whale researcher at the Pacific Whale Foundation and lead author of the new article, told the Guardian: "This discovery challenges our preconceived notions about humpback whale behaviour. While we have long recognized the complex social structures of these incredible creatures, witnessing the copulation of two male whales for the first time is a unique and remarkable event."

The researchers speculate that homosexual behaviour among humpback whales may be part of practicing sex or asserting dominance over peers. It has long been known that other marine mammals, including dolphins and orcas, can exhibit homosexual behaviour.