Biologists, long stumped at figuring out how old whales are, lucked out when a 50-ton bowhead caught off Alaska came with a telltale clue: fragments of a harpoon lodged in a shoulder bone.

The weapon was used more than a century ago by whalers from New Bedford, Massachusetts, enabling researchers to estimate that the whale was at least 115 years old and providing more evidence for their long-held belief that the bowhead whale is one of the longest-living mammals on earth, surviving for up to 200 years.

"It's pretty rare that you get the chance to date the age of a whale," said John Bockstoce, the whaling historian at the New Bedford Whaling Museum who analyzed the fragments.

"We're all finding it very interesting," he said Tuesday.

A biologist in Alaska spotted the pieces of the projectile as they were being pulled from the whale's blubber by Eskimos who had killed the animal last month.