Ellie West, RSPCA animal rescue and wildlife officer, said: “The pup was dehydrated and in a thin body condition with obvious rolls of skin that should have been filled with fat/blubber.”
She said she noticed marks on the seals back that were similar to spray marks the RSPCA put on seals after they were assessed but these were a different colour.
She contacted the British Divers Marine Life Rescue which confirmed it had marked the seal when it was checked on 7 December at Port Gaverne, north Cornwall.
“In the four days after this, he made his way to St Brides Bay – travelling basically in a straight line – and covering a distance of around 120km,” she said.
“This is a really long swim for a young pup.”