WELLINGTON, New Zealand >> Conservation staff in New Zealand have put down 33 stranded whales after several attempts to refloat them failed.

The pilot whales shot Thursday were the last of 99 that stranded themselves Monday on Farewell Spit on the South Island. Department of Conservation area manager John Mason says staff and hundreds of volunteers had tried all week to get the whales refloated.

He says they thought they were successful Wednesday when they got the whales into deep water — but were saddened Thursday to find that they had swum back ashore. He says the condition of the whales had significantly deteriorated.

As well as the 33 whales that were shot, 36 had died naturally since Monday and 17 were successfully refloated. Thirteen remain unaccounted for.