Coast Guard Beach in Eastham was closed for about an hour on Sunday morning after local resident Bruce Langsen took the photo while on the beach with his son. He says he thinks it was a great white shark feeding on a seal.
There were several surfers in the water at the time, but no humans were hurt.
Coast Guard Beach is part of the federally run Cape Cod National Seashore, so park rangers as well as local authorities were notified.
Shark sightings have become more common on the Cape as the area’s seal population has exploded.