08/20/2010 12:04 pm ET | Updated May 25, 2011

Pilot Whales Wash Up On New Zealand Beach (VIDEO)

WELLINGTON, New Zealand (AP) - New Zealand whale rescue volunteers were racing against time Friday to save 15 pilot whales stranded on an isolated northern beach -- after rescuers reported 58 of the pod had already died. (Scroll down for video)

Kimberly Muncaster, chief executive of the Project Jonah whale aid group, said the 15 surviving whales were in "fairly poor condition."

The whales probably stranded during the night, which is why so many died before they were discovered, said Carolyn Smith, the community relations program manager for the Department of Conservation.

Far North Whale Rescue, a team of trained volunteers, was working with the department to try to refloat the survivors, she said.

At least five people were working to assist each stranded mammal, which weigh up to 3,300 pounds (1,500 kilograms) each.

Heavy rain and wind in the area near the North Island town of Kaitaia was both a help and a hindrance, Smith said. The whales would not dry out on the beach, but it made conditions difficult for rescuers.

New Zealand frequently sees several mass whale strandings around its coastline, mainly each summer as whales pass by on their migration to and from Antarctic waters. Scientists have not been able to determine why whales become stranded.

A pod of 101 pilot whales stranded on the same beach in 2007.

The country has one of the world's highest rates of whale strandings, according to the Department of Conservation. Since 1840, more than 5,000 strandings of whales and dolphins have been recorded around the New Zealand coast.

See video of the stranded pilot whales here: