The body of a leatherback turtle, a federally protected endangered species, washed ashore at South Beach on Monday. Volunteer members of the turtle stranding committee said the cause of death was not immediately apparent.

“There was no sign of an injury,” said Felix Neck Wildlife Sanctuary director Suzan Bellincampi. Ms. Bellincampi said the turtle was in a state of decomposition and had likely been floating for awhile before washing ashore.

Leatherbacks, the largest of all sea turtles, can grow up to six and a half feet and weigh up to 2,000 pounds. Ms. Bellincampi said she estimated the turtle to be about four to five feet in length. “It was pretty big, pretty bloated,” she said.

Leatherbacks are common in deep open waters around the Vineyard, but not often seen. The reptiles are migratory, and at this time of year are typically found off the coast of Long Island and New Jersey as they make their way south to spawn.

“I can’t tell you what happened to this animal, but it’s possible that he died somewhere along the way and was brought back by the tides,” she said.

Members of the turtle stranding committee collected a DNA sample for research purposes, but did not perform a necropsy on the animal, making it unlikely that a cause of death will be discovered.

Ms. Bellincampi noted that turtles carry zoonotic diseases and should only be handled with protective gloves. “When people find things like that out on the beach, don’t touch it,” she said. “You don’t want your dog sniffing at it, biting at it. It’s not a good idea,” she said. The turtle will likely be washed back out to sea by the tides.

The leatherback is the only sea turtle that lacks a hard, bony shell, making it susceptible to injury from boats. This summer, two leatherbacks were found dead near Falmouth in one week. The first was believed to be struck by boat propellers; the second was believed to be tangled in a fishing net. Another leatherback turtle was found dead on the shore around Seven Gates Farm in Chilmark in September. The cause of death was not apparent, according to Gazette reader Tom Guiney, who reported the sighting.

In 2008, federal officials made a point of cautioning boaters in the waters off Massachusetts to keep a sharp lookout for leatherback turtles, among the world’s largest reptiles, were present in nearby waters in record numbers.

Islanders who discover any stranded marine animals are urged to call the New England Aquarium’s 24-hour hotline, 617-973-5247.