Keith Ellenbogen and his colleagues aboard a Stellwagen Bank National Marine Sanctuary boat had seen a fin on the morning of Aug. 17, about 6 miles north of Provincetown. The slow movement of the fin, and the giant circle it made in the flat water, led the group to decide it must be a basking shark, which are not generally dangerous to humans.
Ellenbogen, who is photographing wildlife in the sanctuary in the first of a three-year grant, grabbed his camera and slipped into the water in a wetsuit, mask, snorkel and flippers.
But as the murky water cleared just under the surface, he realized the fin belonged to a great white shark, approximately 16 feet long, that was also near the surface and swimming straight toward him.
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