Some 477 pilot whales have died after stranding themselves on two remote New Zealand beaches over recent days, officials say. None of the stranded whales could be refloated and all either died naturally or were euthanized in a "heartbreaking" loss, said Daren Grover, the general manager of Project Jonah, a nonprofit group which helps rescue whales. The whales beached themselves on the Chatham Islands, which are home to about 600 people and located about 800 kilometers (500 miles) east of New Zealand's main islands. The Department of Conservation said 232 whales stranded themselves Friday at Tupuangi Beach and another 245 at Waihere Bay on Monday. The deaths come two weeks after about 200 pilot whales died in Australia after stranding themselves on a remote Tasmanian beach. Mass strandings of pilot whales are reasonably common in New Zealand, especially during the summer months. Scientists don't know exactly what causes the whales to strand, although it appears their location systems can get confused by gently sloping sandy beaches. Grover said there is a lot of food for the whales around the Chatham Islands, and as they swim closer to land, they would quickly find themselves going from very deep to shallow water. "They rely on their echolocation and yet it doesn't tell them that they are running out of water," Grover said. "They come closer and closer to shore and become disoriented. The tide can then drop from below them and before they know it, they're stranded on the beach."