WELLINGTON, New Zealand — More than 140 pilot whales died after beaching themselves in southern New Zealand, with half being euthanized by conservation workers in a “deeply saddening” decision after their discovery came too late to rescue them, officials said Monday.

The stranding, in an isolated part of Stewart Island, off the coast of the South Island, was the largest in New Zealand since 250 pilot whales died last year in one of the worst such incidents in the country’s history.

The beached whales on Stewart Island were discovered in two separate groups, or pods, just as several other whale deaths and strandings were reported around the country over the weekend.

The Department of Conservation said Monday that as many as 145 whales beached themselves at Mason Bay, on the island’s west side, where they were discovered by a hiker on Saturday afternoon.