The state’s leading shark expert confirmed that the woman who was injured in the water off Norton Point last week was bitten by a shark. 

Shark biologist Greg Skomal said Wednesday that he had studied pictures of the wound, conferred with hospital staff and talked to other shark experts to come to the conclusion that the woman’s lacerations were caused by a shark.

“It’s most certainly a shark bite,” Mr. Skomal said in an interview. 

This is believed to be the first unprovoked shark bite in Island history and the first bite in Massachusetts since the death of a boogie boarder off Cape Cod in 2018.

The shape of the wound and tooth marks indicate that the shark bit the woman before quickly retreating. What kind of shark was involved, Mr. Skomal couldn’t say for certain, but he believed it was a sandbar shark based on the characteristics of the wound and the species’ abundance around the Vineyard.

“We can’t be 100 per cent sure in these situations because nobody saw the shark,” he said. “But we concluded that it is the most likely candidate.” 

Also known as brown sharks, sandbar sharks come to Vineyard waters in late June and leave in the fall, similar to other migratory fish. 

Mike Creato, the biplane pilot who takes people on tours around the Island, said he often sees the shark off South Beach and Norton Point. Mr. Skomal said fishermen he has talked to have seen them close to shore. 

“They get them relatively close to shore, within casting distance,” he said. 

Brown sharks feed on a variety of fish and invertebrates and tend to stick to the ocean floor. Because there were no witnesses of the incident, it is hard to tell how the scene unfolded, but there are theories. 

“It seemed that she was exiting the water and the shark was likely cruising by and in that split second it saw her and interpreted her as a threat or a prey item,” said Mr. Skomal. 

The shark likely did not mean harm, and most shark bites are accidents, he added. 

“It was not a bite that resulted in the consumption of any flesh,” Mr. Skomal said. 

The incident unfolded on August 31. Rescuers were called to the Edgartown beach and transported the woman, who is in her late 20s, to the hospital with injuries that weren’t considered life-threatening. At the time, town officials said the wound was consistent with a shark bite, but couldn’t be certain. The beaches were closed to swimming for several hours. Days later Chilmark closed its beaches to swimming after shark sightings. 

The only other bite on the Vineyard Mr. Skomal could recall was several decades ago. He was called to the hospital in the late 1980s for a sandbar shark bite. In that instance, the shark had been caught by an angler and bit a man who had grabbed the shark by the tail.

While news of a shark bite may make some nervous, Mr. Skomal said the likelihood of being bitten remains low, especially if swimmers remain cognizant of their surroundings.