WELLINGTON, New Zealand - Oil refinery workers helped rescue 40 beached pilot whales in northern New Zealand Friday - but another 37 of the whale pod died on the sandy beach, a Department of Conservation spokeswoman said.

By early afternoon the rescued whales were less than a mile off the shore and "starting to swim strongly" out to sea, spokeswoman Sue Campbell told The Associated Press from the North Island city of Whangarei, near the stranding site.

Boats were patrolling near the whales to encourage them to continue heading out to sea rather than return to Ruakaka beach.

About 70 volunteers and 15 department staff were standing by in case the whales turn back toward shore or begin to swim into nearby Whangarei Harbor, she said.

Workers from the nearby Marsden Point oil refinery, together with local volunteers, were already helping to refloat the whales when the department was advised of the stranding, she said.

The beached pod marked the first mass stranding of the season. New Zealand has several mass whale strandings each summer.

The biggest recorded mass stranding on the New Zealand coast involved 1,000 pilot whales on the Chatham Islands in 1918, and the largest in recent years saw 450 of the same species beached on Great Barrier Island in 1985. Rescuers successfully refloated 324 of those mammals.

Whale experts have been unable to explain why the mammals apparently swim into dangerously shallow waters.