A beaked whale that washed up on a beach in Massachusetts is only the second example in 15 years of the deep water species coming ashore in the state, officials say.

The carcass of a 17-foot-long female, weighing around a ton, was washed onto rocks at Jones Beach in Plymouth.

Sightings of beaked whales occur so seldom that an official estimate of their wild populations has never been possible for marine biologists, said New England Aquarium spokesman Tony LaCasse.

"It's a glimpse into a habitat that's not so far away, but it's still a world away," he said. "They live in a world of their own."

Their normal habitat is hundreds of miles out in deep ocean waters, experts said, with the waters off New England believed to be the southern limit of their range, which extends north into the sub-Arctic.

There are some 20 species of beaked whales known to science; initial examination of the Massachusetts example suggested it was a Sowerby's beaked whale, which normally lives in waters as deep as 5,000 feet.

They are thought to feed mostly on squid or cod.

Named after James Sowerby, an English naturalist who first described them in 1804 when one washed ashore in Scotland, the species is reclusive, avoiding ships at sea, and is rarely sighted.

Aquarium biologists from the Woods Hole Oceanographic Institution in Massachusetts performed a necropsy on the whale, estimated to be between seven and eight years old.

It bore no evidence of trauma that might suggest it had been struck by a ship or become entangled in fishing nets, LaCasse said.

Why it washed up in Plymouth, far from its usual habitat on the continental shelf, remains a mystery, he said.

"They're very, very rare. That animal would have no business in Cape Cod Bay even as a transient area," he said. "They're in small pods of three to seven way, way, way off the coast."