Photographers have captured images of humpback whales engaging in sexual activity for the first time – and the mammals being intimate were both males.

The behaviour of humpbacks has fascinated scientists for decades – but a study published this week features the first photos of the species having penetrative sex, its authors have said.

It was written by marine biologist Stephanie Stack and the two photographers who captured the encounter, Lyle Krannichfeld and Brandi Romano.

The whole discovery was “opportunistic,” they said, as the whales “slowly approached” the photographers’ boat while they were out in waters west of the Hawaiian island of Maui in January 2022.

The photos show a healthy and strong male whale penetrating another, who appears unhealthy or injured and emaciated, the study said.

The mammals – which usually range from 12 to 16 metres long – circled the vessel “several times” with the healthier whale “pursuing” the other.

After around half an hour, the healthy whale held the other in place with its pectoral fins and the sex took place.

The authors suggested the emaciated whale may have approached the boat to seek cover from its companion.

They said it remains unknown whether same-sex sexual activity would take place between two healthy males.

Upon returning to the shore and looking at the photographs, Krannichfeld said they immediately knew they’d captured “a once-in-a-lifetime encounter”.

“The whales are a big part of our lives here in Maui,” he told Sky’s US partner NBC News.

]”Everybody that’s involved with them and who photographs them kind of realises that that’s never been captured.

“Mating and birth are the two main things that are still kind of unknown.”

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They shared the photos with Ms Stack, who identified both whales as male.

This isn’t the first time same-sex behaviour has been observed in the animal world, with the study noting it has previously been observed in walruses, Amazon river dolphins and grey seals.

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