On June 7 of this year, a British diver had a remarkable encounter with a rare and prehistoric shark. Megamouth sharks (Megachasma pelagios) are hardly ever seen alive, but this 5-meter (16.4-foot) behemoth emerged from the depths to star in some truly remarkable footage.

The person who can be seen swimming alongside the megamouth is Bee Smith, a team member at Shark Education who is currently working on a documentary about megamouth sharks in Taiwan. In a TikTok video, Smith shared that the search for megamouths got a time frame after finding out she needed to be back in the UK to appear on Springwatch. Fortunately, the megamouths did make an appearance.

“From the first moment that I saw each of the megamouths it didn’t seem real,” said Smith in a Compass Media statement emailed to IFLScience. “When I was with them I was focused on doing what needed to be done for the project. It was only really after the encounters were over that I could process what happened, and I was so happy when I got back on the boat.”

“Personally it meant a lot because I have been obsessed with sharks since I was a child. But more importantly, because it meant I had finally gotten the knowledge and footage I needed for the documentary.”

Megamouth sharks were first discovered back in 1976 when an individual was seen off Hawaii. Since then, there have only been 279 sightings, partly due to the fact that they are deep-water sharks that only come to the surface to feed on plankton at night.

It’s more common to see dead megamouth sharks, either after washing up on the shore (like this pregnant female) or getting caught in fishing nets. According to Smith, the majority of sightings come from fisheries catches in Taiwan, where in 2020 a ban on megamouth catch was introduced.

“This means that if a megamouth is caught it must be returned to the ocean immediately, whether it is dead or alive,” said Smith. “I am working on a project investigating this catch and release policy, for a documentary.”

“I went out on the boats of the drift net fishers who have caught megamouths to film their fishing. If they caught one my team would help cut it free and film it and also take tissue samples and place acoustic tags on them.”

The remarkable video joins a select archive of megamouth shark footage, including a 2023 world-first sighting of two megamouth sharks together. As for why they were hanging out, one theory is that they were foraging, or they may have had spicier motivations…