A 13-foot pilot whale washed up on Lucy Vincent Beach in Chilmark over the long weekend. Adam Kennedy, a senior biologist at the New England Aquarium, said the whale was likely dead when it washed ashore.

Mr. Kennedy said the animal was discovered half-buried in the sand by the tides last Friday. Only its head and front fin were visible; the rest of its body was obscured. The conditions were “very unusual,” Mr. Kennedy said.

Volunteer responders for the New England Aquarium stamped the whale with the date it was found, in case it should wash back out to sea and come ashore elsewhere, and recorded the whale’s measurements in the aquarium’s database of marine mammal strandings.

Although other species of whales, including humpback, sei and pygmy, have washed ashore on the Vineyard in recent years, this is the first pilot whale recorded, he said.

Pilot whales are a relatively small cetacean species, reaching lengths of about 20 feet when fully grown. The whales are known for stranding en masse. Earlier this fall, a large pod stranded itself on a beach in Scotland, and just yesterday 28 pilot whales beached themselves in New Zealand’s Golden Bay.

Pilot whales travel in large pods, Mr. Kennedy noted. When an animal is isolated, like the Lucy Vincent whale, “it usually means something’s wrong.”