Police are investigating after two "sadistic" motorcyclists were seen riding over a seal pup on a beach.
The pair were spotted riding over the pup twice on the beach near Sea Palling, Norfolk, on Friday morning.
"It's not clear whether the seal pup was alive at the time the bikes ran over the pup, but obviously this is a disturbing incident," said PC Thomas Walsh, from Norfolk Police.
The incident "smacked of sadism", a volunteer seal group leader said.
Peter Ansell, chairman of the Friends of Horsey Seals, said: "A lady phoned me up, very upset that she'd witnessed a couple of trail bikers drive over a seal pup just north of Sea Palling beach - not just once... but they turned back and drove over it again.
"She sent me photographs of the tyre tracks and the pup.
"We don't know whether the pup was alive or dead.
"I really hope it was dead."
"I'd hate to think that anybody could be so sadistic as to drive over a live pup, turn round, come back and have another go at it.
"[It] almost smacks of a certain sadism in my mind - run over a dead body, come back and mow over it again."
The pup's body was taken to the RSPCA hospital at East Winch, near King's Lynn, where "some sort of a post-mortem" would be carried out by a vet, Mr Ansell said.
He said he hoped that would determine whether the seal had died of natural causes before the motorcyclists ran over it.