Nearly a century ago, the ichthyologist David Stead recorded a strange unease among the lobstermen of Port Stephens, Australia. Although their livelihoods depended on the sea, the men could not bring themselves to venture out to their favorite crayfish spot near Broughton Island for fear of what they had just seen.

Out there, Stead related almost half a century later in his book Sharks and Rays of Australian Seas, was a monstrous, ghostly white shark of such mind-boggling size that apparently no one could agree exactly how big the leviathan was. The shark was big enough to swallow lobster pot after lobster pot, at the least, but the size estimates Stead drew from the workers ranged from 115 feet to an