‘It sounds silly but I thought it was a person in the water waving,” says Kurt Lander, skipper of the Yellowfin charter boat, based out of Brighton. But when he grabbed his binoculars, he realised the fluttering movement he had noticed in the middle of the Channel shipping lane was a pair of sunfish.

The huge fish were lying on their sides and flapping their fins. “Apparently, they do it as a visual attraction to birds,” he says. “They’re trying to get the birds to eat the parasites off them.”

Lander has seen the huge fish with their unusual round bodies before. But the difference is that those that he spotted this year are part of a surge in sightings of the species off British shores this summer, probably as a result of a marine heatwave.