About 500 pilot whales died in mass strandings on New Zealand’s remote Chatham Islands, the government said on Tuesday.

No rescue effort could be carried out as there are too many sharks in the waters around the islands which pose a danger to both human beings and the whales.

On Friday, 250 beached pilot whales were found at Chatham Island, and then three days later another 240 were reported on Pitt Island, according to New Zealand’s Department of Conservation.

“Due to the risk of shark attack to both humans and the whales, the surviving whales were euthanised by our trained team to prevent further suffering,” an AFP report cited Dave Lundquist, a government technical marine advisor, as saying.

“This decision is never taken lightly, but in cases like this it is the kindest option.”

The bodies will be left to decompose naturally at the site.

Scientists do not fully understand the reason for strandings, but some believe pods go off track after feeding too close to shore.

Around 300 animals get stranded on beaches annually in New Zealand, according to official figures.