Wildlife officers have been stunned to see video of a Perth man slapping the rear of a 2000kg southern elephant seal that came ashore at Sorrento Beach, prompting a warning for the public to stay away from the animal.
The sub-adult male drew big crowds to the northern suburbs beach, after coming ashore on Wednesday.
Department of Parks and Wildlife (DPaW) officer Matt Swan said the seal had most likely spent a long period hunting in the water and was using a "haul-out period" to rest on the beach.
The mammals hunt far off the coast in deep waters, so that makes them very tired.
Mr Swan urged curious beachgoers to keep a safe distance of at least 30m and warned people not get in between the seal and the water.
Seals can inflict a bite similar to that of a large dog and can move faster than humans.
"We are asking beachgoers not to approach the seal and to keep their dogs on leads as seals' behaviour can be very unpredictable," Mr Swan said.
"If it is harassed by people trying to get too close, it may feel threatened and react aggressively."
DPaW said seals were generally found in waters around sub-Antarctic islands.
While it was unusual for one to haul out this far north, there had been previous occurrences, the department said.
A large male that hauled out in the Exmouth area remained there for five years.