Hundreds of pilot whales dead after mass stranding in Chatham Islands

A pilot whale stranding on Stewart Island in 2018. Photo / Supplied

More than 215 pilot whales died after beaching themselves on the Chatham Islands over the weekend.

The pilot whales, which are members of the dolphin family, started to become stranded on the remote islands' northwest on Friday.

The whales all died, with attempts to refloat them too dangerous due to a risk of a shark attack, according to the Department of Conservation.

"We do not actively refloat whales on the Chatham Islands due to the risk of shark attack to both humans and the whales themselves," DoC said in a statement.

"Iwi and imi were present to support."

"All the stranded pilot whales are now deceased and their bodies will be left to decompose naturally on site."

Project Jonah, a not-for-profit organisation that helps rescue animals and protects marine mammals, wrote that strandings on the Chatham Islands are problematic and make rescues a difficult task.

"The Chatham Islands is a challenging spot for stranding response, known for great white sharks, remote beaches, and a resident population of less than 800 people."

Strandings are "not uncommon" in the Chatham Islands it says, noting that the largest recorded event involved an estimated 1000 whales in 1918.

Pilot whales — which can grow to more than six metres (20 feet) long — are also highly sociable, so they may follow podmates who stray into danger.

In New Zealand, about 300 animals beach themselves annually, according to official figures, and it is not unusual for groups of between 20 and 50 pilot whales to run aground.