The Department of Conservation is investigating after a beachgoer found a protected leopard seal shot in the head.

Shane Searle found the dead animal on a beach near Dargaville on Friday morning. He had seen the same seal the day before, and was shocked someone would needlessly kill it.

The seal had been shot in the face.

"Especially when it was alive and looking so healthy the day before," Searle told the Herald.

"There are a lot of stupid people in this world, and people do things they don't think about at the time. And when it has actually happened they may have a bit of regret now, but it's a bit late … once you pull that trigger, she's pretty certain."

The killing happened on a stretch of beach near Te Kopuru, south of Baylys Beach.

DOC operations manager for the Kauri Coast, Stephen Soole, told Newsroom the body of the seal would be taken today with an autopsy likely. Police would be involved in an investigation.

Leopard seals normally live in the Antarctic pack ice, but during autumn and winter can move northward through the Southern Ocean.

The animals have at times spent a year or more in New Zealand waters, and are protected under the Wildlife Act 1953 and the Marine Mammals Protection Act 1978.