One of the dead seal pups captured on camera
A bull seal has been caught on camera killing seal pups for the first time in Welsh waters, says the Countryside Council for Wales (CCW).
It says marine experts have no real idea what triggered the two attacks.
They were photographed during the seal pupping survey on Skomer Island, off Pembrokeshire, late last October.
Images have now been posted on You Tube and CCW wants to hear from anyone anywhere in the world who has witnessed anything similar.
CCW manages the Skomer Marine Nature Reserve and regularly surveys and monitors the Atlantic grey seals who live there.
A spokeswoman said 77% of the 132 seal pups born last year survived and, apart from the killings, surveyors said this was a typical year.
Naturalist David Boyle who saw and photographed the two separate seal pup killings described what he saw.
"I've been surveying seals for several years, and although many people think of them as cute, during the breeding season the bulls can be fierce as they defend their territory," he said.
"In the scene I witnessed, the bull seal seemed to be deliberately drowning the newly moulted pup.
"He then gouged a massive piece out of its neck.
"It was a gruesome sight that reminds us that seals are wild and unpredictable creatures."
Skomer is owned by the Countryside Council for Wales and managed by the Wildlife Trust of South and West Wales.