Police have launched an investigation after six seal pups were found decapitated at a popular New Zealand bay.

The bodies of the 11-month-old fur seals were discovered floating near the shore by a tour operator in the country’s South Island.

They are thought to have been killed elsewhere and dumped from a boat at the scenic spot, according to the Department of Conservation (DOC), which called the animals’ deaths “cruel and senseless”.

Under New Zealand’s Marine Mammals Protection Act, it is a criminal offence to harm fur seals.

“Due to the disturbing, brutal and violent nature of this crime against defenceless seal pups, it has been reported to the police,” said DOC operations manager Andy Thompson.

The seals’ bodies were found at Scenery Nook, a remote but popular bay on the Banks Peninsula, close to Christchurch. Their heads have not been found.

Three of the pups have been buried by wildlife rangers and the others have been sent to Massey University for autopsies.

“While the necropsy will determine the exact cause of death, we believe it’s incredibly unlikely sharks would have bitten the heads off six seals but left the bodies untouched,” Mr Thompson said.

The seals’ bodies were found floating off the coast of the Banks Peninsula (Bernard Spragg/Creative Commons)

Authorities have appealed for witnesses to report any boats seen in the area in the past week.

There have been several previous cases of people injuring or killing seals after becoming frustrated over low fish numbers in the ocean, according to the DOC.

Mr Thompson said: “Regrettably, antagonism towards seals is often due to the misplaced belief that seals are eating large amounts of fish species valued for human consumption. That isn’t the case.