Rescuers attempt to save false killer whales on the beach, in Kommitjie, South Africa, 30 May 2009

Fifty-five whales that beached themselves in South Africa have died or been euthanized after efforts to save them were not successful.

South African marine authorities shot about 40 of the whales on Saturday, while the rest died of exhaustion and stress.

The whales had stranded themselves on the beach near Cape Town earlier in the day.

Rescue teams tried to push the whales back to the ocean using earth-moving equipment.  But heavy surf pushed the giant mammals back to the beach.

Scientists plan to take samples from the carcasses to try to determine why the whales came ashore. 

The animals, originally identified as pilot whales, turned out to be false killer whales.

False killer whales look like their close relative, the killer whale, but are smaller and darker in color.  They can grow to nearly six meters in length.

The whales are social creatures that travel in groups.  Partly because of this social nature, they sometimes are involved in mass strandings.

Some information for this report was provided by AP and Reuters.