For years, scientists have been baffled by sightings of the sixgill shark in Puget Sound, off the coast of Seattle. The heavy-bodied sharks, which reach up to 13 feet in length, are found worldwide at the bottom of the ocean. But scientists couldn't understand why the sharks inhabited the waters of Elliot Bay and Puget Sound.

"The presence of the shark here in Elliot Bay and Puget Sound was kind of a little-known secret among scientists, commercial fishermen, and maybe local scuba divers, and the reason it's here is part of the big mystery," said Jeff Chrstiansen, a senior biologist with the Seattle Aquarium.

One reason, it turns out, is that the prehistoric-looking shark knows something about family.

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