The RSPCA is investigating the deaths of five grey seals, three of them beheaded, found by a passer-by on a beach at Whitley Bay, North Tyneside.
All of the seals were juveniles. The eldest was thought to have been no more than a year old and the youngest just a few weeks.
RSPCA acting chief inspector Mark Gent said: "This was a very upsetting thing to come across and has caused a lot of distress to the person who found them. These were very young animals; one of them was what is often described as a white coat, and was just a few weeks old. We want to hear from anyone who knows anything that might help us in our investigation as soon as possible."
One of the seals was tagged. Investigations by the RSPCA have found that it was part of a study into the survival and reproductive success of seals by the Sea Mammal Research Unit, St Andrews, Fife. Seals are protected by law.