Diving into the green, murky, nutrient-rich waters at the mouth of the estuary was something extraordinary. As I descended down 20 metres, I waited in the gloom, unsure at first of what I was seeing. It was like I was watching an old photograph slowly develop in a chemical bath. Gradually, the image emerged, and I could see a squadron of prehistoric giants gliding overhead, slow and silent, some up to 10 metres long. They seemed indifferent to my presence, their movements so deliberate and slow – it was almost as if time itself had slowed down. Occasionally, one would glide right up, just out of curiosity, before drifting away again. It’s humbling to be in the company of such ancient creatures, knowing that what I’m witnessing is truly unique in a global context,” remembers Nick Pfeiffer, a marine researcher and photographer, who captured this awe-inspiring and extraordinary moment.

In September 2024, Pfeiffer found himself immersed once again in the mysteries of these ancient creatures off the west coast of Ireland. Hundreds of these magnificent sharks glided below the surface, their immense bodies moving together in a quiet, rhythmic dance. They circled in a ‘torus’ formation, a behaviour believed to be part of courtship, but still cloaked in mystery.

2024 was a landmark year for this mysterious behaviour. Simon Berrow, chief science officer of the Irish Whale and Dolphin Group (IWDG) and a long-time collaborator with Pfeiffer, along with his colleague Helene, bumped into this phenomenon in July while out on a 56-foot research vessel. Initially, unsure they would encounter this torus behaviour so early, they were cautious about sharing their findings. However, by September, thousands of sharks had gathered. “It was remarkable. The scale of the aggregation was unlike anything we had seen, there must have been thousands of basking sharks,” Berrow recalls.

The torus behaviour of basking sharks is a unique sight. Different groups of up to 20 sharks swim slowly in tight, synchronised circles with several circles, toruses, occurring simultaneously. At times, they swim in parallel, forming lines that extend for hundreds of metres. These circles and parallel formations create a dynamic and mesmerising spectacle. With their mouths closed, the sharks move calmly, their dark silhouettes cutting through the water from the surface down to about 12-30 metres deep. The scene is serene and otherworldly, as multiple groups of sharks perform this slow, graceful dance beneath the ocean’s surface.