A large number of whales have stranded at the Chatham Islands.

The Department of Conservation said the pilot whales had come ashore at the southern end of Hanson Bay, near the township of Owenga in the Chatham Islands.

DoC said it was notified last evening of the stranding of 80 to 90. As it was too late to act, DoC staff returned at first light today to assess the situation.

When staff arrived at the scene about 30 to 40 pilot whales had re-floated themselves and returned to sea, however 51 whales remained. All but one were dead. It was decided to euthanise this whale, due to its very poor condition.

Between 80 and 90 whales were stranded. Photo/DOC
Between 80 and 90 whales were stranded. Photo/DOC

DoC Chatham Islands Operations Manager Dave Carlton said, "There was no likelihood of being able to successfully save the remaining whale. Sadly, the decision was made to euthanise. It was the most humane thing to do."

"This is always an awful decision to have to make."

DoC has notified local Moriori, and Ngāti Mutunga iwi. Staff are working with locals to bury the whales at site.

Skin and blubber samples are being taken from the latest whales to have stranded and will be sent to Massey University scientists in an attempt to understand more about this species.

Marine mammal strandings are a relatively common occurrence on New Zealand shores. This is the second large stranding of pilot whales this week. On Rakiura/Stewart Island on Monday there was a mass stranding of 145 pilot whales. Two pods stranded at the southern end of Mason Bay, approximately 2km apart. None survived.

DoC said exactly why whales and dolphins stranded was not fully known but factors could include sickness, navigational error, geographical features, a rapidly falling tide, being chased by a predator, or extreme weather. More than one factor might contribute to a stranding.

DoC Rakiura operations manager Ren Leppens said half of the whales at Stewart Island had already died by the time they were found and due to the condition of the remaining whales and the remote, difficult to access location, the decision was made to euthanise the remainder.

Ten pygmy killer whales also stranded on Ninety Mile Beach in Northland on Sunday.