A group of tourists who ventured out to cage-dive with great white sharks off Australia were treated to something even more special when a female swam on her back next to their boat.
Video recorded by U.K. tourist Wendy Bower-Leech shows the female great white going belly-up beside the charter boat off the coast of Lincoln, South Australia in early October. The shark emerges upside down from under the boat and swims in an arc for about 12 seconds.
“Is that normal?” one passenger can be heard asking, amid cries of astonishment from the others on board.
“No,” another person replies.
One of the guides adds: “I’ve never seen a shark do that before.”
Calypso Star Charters, which operates the shark cage-diving tour, posted Bower-Leech’s video on Instagram on Friday.
“Check out this amazing footage … of this very curious female shark showing off swimming on her back,” the charter company wrote.
Sharks do not typically swim upside down. However, they do flip over on rare occasions to assume a position known as tonic immobility, according to the Shark Trust, a U.K.-based non-profit dedicated to promoting shark conservation.
Tonic immobility puts the shark into a relaxed, trance-like state, according to the Shark Trust. Biologists often use this technique when handling much smaller sharks.
Dive instructors aboard the boat were as astonished as their customers, according to Calypso Star Charters. The company says the boat’s skipper, Dave Clayfield, has never seen such behaviour before.
Bower-Leech said she feels lucky to have captured the rare moment on video.