The island, which is a national wildlife refuge, is home to hundreds of seals and also a favored feeding ground of several species of sharks.
Capt. Bob Littlefield is sure the shark he saw rip a seal in half yesterday afternoon was a great white.
"It was a quite a bloody mess," said Littlefield, who has been a captain on Cape Cod for 32 years.
Littlefield was steering a 42-foot, high-speed catamaran owned by Monomoy Island Excursions of Harwich Port on the ocean side of Monomoy, where hundreds of seals were sunning and swimming, when suddenly there was a commotion in the water.
Littlefield, who said he had always wanted to see a shark eat a seal, turned the boat toward the area, which quickly became red with blood. As the boat got closer, the shark went under, taking half of the gray seal with it. The tour captain estimated the seal to be 300 to 400 pounds, and the shark to be between 14 and 16 feet.