(AG / 23-08-10) Nine pilot whales have been rescued from a group of 58 who were stranded on Friday on a beach in northern New Zealand.

Authorities found only 15 of the whales alive and managed to return 13 to sea for the weekend, but four stranded again and died, said Sioux Campbell , spokesman for the Department of Conservation. "Fortunately, we have not seen the whales today, which is good news. We are very happy to have saved the whales with the help of the community," said Campbell.

About 70 volunteers worked tirelessly to keep afloat and breathing mammals despite weighing a ton and a half.

According to the New Zealand authorities, most of the whales died because they stranded during the night and it took hours to discover them.

Two years ago, more than one hundred pilot whales were caught on the beach in New Zealand that, like Australia, sees every year hundreds of marine mammals killed in their coasts.

Scientists do not know the reason why some species of whales die on the beaches. One of the possibilities is that they are attracted by sonar of large ships or they maybe follow a group leader disoriented by illness.