Campaigners said seals often investigated the floating toys as playthings, but once a ring slips over their head it becomes impossible to remove.
As the animal grows, the plastic cuts deeper into the skin, causing severe pain and infection. Sayer warned: “One ring can kill more than one marine creature, so the creature dies, the ring floats again, and goes on having another life.”
A seal called Wings who was found in St Ives in 2023, was an example of the damage that rings can do, said the Cornish Seal Sanctuary which cares for seals snagged by flying rings.
A ring had caught tightly around Wings’ neck, but it was removed after the female seal was successfully rescued.
Campaigners said it had been around her neck for two weeks and begun to strangle her.
They said many seals injured by the rings were never found or could not be saved.