Six decapitated fur seals have been found at Banks Peninsula near Christchurch.
The Department of Conservation says the 11-month-old seals were discovered floating in the tidal wash by a tourism operator at Scenery Nook on Monday.
DOC believes the seals were killed elsewhere before being dumped from a boat and left to be found by visitors to the scenic area.
There was no evidence of the seals' heads and the incident has been reported to police.
DOC Mahaanui Operations Manager Andy Thompson says the deaths are "cruel" and "senseless".
"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."
DOC is appealing to members of the public for any sightings of boats believed to have been in the area since late last week.
"There were a lot of boats on the water enjoying the warm weather last weekend."
If anyone saw anything suspicious they are urged to contact DOC on 0800 HOT DOC (0800 362 468).
Mr Thompson says there are several known cases of people injuring or killing seals after becoming frustrated over low fish numbers in the ocean.
A police spokesperson told Newshub they were notified of the incident on Wednesday and will assist DOC with their investigation.
Newshub.
