The newborn grey seal, believed to be just two days old, was spotted on a beach at Castlemartin Range on Wednesday, September 16.
Pembrokeshire Coast National Park Authority staff cordoned off the area with “No Access” signs to protect the vulnerable animal from disturbance.
By Thursday, September 17, the pup was resting peacefully, but by Friday, September 18, it had disappeared.
Grey seal pups are very vulnerable during their first three to four weeks of life, and they need “space and peace”.
A spokesperson for Pembrokeshire Coast National Park Authority said: “On Wednesday, a grey seal pup thought to be just two days old was found on a beach on Castlemartin Range.
“Our team put up ‘No Access’ signs and cordoned off the beach to protect it from disturbance.
“On Thursday, the pup was sleeping peacefully. By Friday, there were human and dog footprints across the beach and the pup was gone.
“Further checks on Saturday and Sunday found no sign of it”.
Footprints appeared on the beach, despite signs urging members of the public to stay away (Image: Pembrokeshire Coast via Facebook)
Members of the public are being urged to respect all beach closures, and to keep dogs away from the area.
The spokesperson continued: “We don’t know what happened to this pup, but the signs and cordon were there for a reason.
“Grey seal pups have just three to four weeks with their mothers to build the reserves they need to survive independently.
“During this vulnerable time, they need space and peace.
“Please stay away from beaches, bays and coves where seals or pups are present.
“Keep dogs away and always respect signs, tape and cordons.
“No beach visit is worth putting a seal pup at risk.
“Please share to help protect them”.