A dead leatherback sea turtle with a severe vessel strike was found washed up on the eastern corner of West Chop Monday, experts at Felix Neck Wildlife Sanctuary confirmed.

The eviscerated sea turtle carcass, which stretched more than two meters in length and likely weighed more than 500 pounds, was spotted by residents walking the rocky shoreline over the weekend and reported to Mass Audubon’s Wellfleet Bay Wildlife Sanctuary, which is the federally-mandated responder to all stranded sea turtles in southeastern Massachusetts.

Mass Audubon coordinated with Felix Neck (also an Audubon sanctuary), which due to pandemic-related restrictions has been assisting with sea turtle stranding responses on the Vineyard. Felix Neck education coordinator Liz Dengenis responded to the turtle sighting on Monday, confirming that the animal had been struck by a vessel.

Ms. Dengenis said the turtle was an adult female, and estimated from its vessel wound and condition that it had been struck at some point early last week.

“It wasn’t too deteriorated; it was decently intact,” Ms. Degenis said. “The eyeballs had been eaten, foraged, and some of the bone was starting to expose on the right side of the turtle, where the propeller had struck it. You could see the slices on the side.”

Approximately a quarter of the turtle’s core was gone, likely from the propeller strike along the top of its carapace, and was dead when it washed on shore, according to Ms. Dengenis.

Suzan Bellicampi, executive director at Felix Neck, said Karen Dourdeville, a sea turtle expert with Mass Audubon, also immediately confirmed that the turtle had died from a vessel strike.

Ms. Belllincampi called the mortality unfortunate and preventable.

Leatherbacks, which can weigh up to 1,500 pounds, are the largest sea turtle species in the world and the fourth largest marine reptile, behind only three crocodilian species. But because leatherbacks have a literally leathery outer carapace rather than the bony shell common among other sea turtles, they can be at particular risk for vessel strikes. And despite their worldwide range, the sea turtles are endangered, arriving in Vineyard waters annually to feed on gelatinous substances, like jellyfish and Portuguese man o’war.

Although sea turtle strandings are much more common around Wellfleet and the Cape, Vineyard experts generally respond to between two and five strandings on the Island every year. The dead leatherback on West Chop was at least the second this season, which runs from late summer through early fall, when the turtles migrate north from tropical waters.

Ms. Bellincampi and Ms. Dengenis said the other sea turtle found this year had washed up on State Beach earlier this summer. But the previous turtle had been sun-bleached and deteriorated by the time it was located. Both said the location of this turtle — on the harbor side of West Chop — was unusual, as was its intact condition.

“Definitely not common,” said Ms. Dengenis. “But now that it’s derby season, this is our biggest education time because so many people are gung ho about being on the water.”

The Martha’s Vineyard Striped Bass and Bluefish Derby has worked with sea turtle experts in the past to ensure boaters are aware of the risks of collision. Sea turtle sightings can be reported at seaturtlesightings.org or phoned in at 888-SEA-TURT (888-732-8878).

Experts generally analyze the sea turtle carcasses to study the impacts of vessel wounds, as well as to check their stomach for plastics. Because of the severity of this turtle wound, experts did not take specimen samples.

But after scanning the turtle for important measurements and photos, Ms. Dengenis noticed something else unusual about the leatherback. The sea turtle had been flipper-tagged with a small, metal marker that contained letters and numbers. Although experts are still waiting to gather more information, they know the tag came from Panama — where the turtle was presumably marked while laying eggs on the beach — meaning it had traveled nearly 4,000 kilometers to get to the Vineyard.

And because the turtle is tagged and has a very distinguishable wound, experts don’t plan to spray paint it with markings, but to leave the turtle as it was found. The tide will likely take it out to see once again.

“In the time I’ve been doing it, I haven’t seen a tagged one,” Ms. Bellincampi said. “That’s my first tagged one . . . we’re still waiting for more info.”

On Thursday, Ms. Bellicampi wrote in an email that after tracing the turtles tags, researchers discovered the leatherback had been marked at Panama's Chiriquí Beach, an indigenous part of the country located in the Ño Kribo Region on March 22, 2019. It was also spotted on the beach twice more, on April 10 and 20, 2019. 

"This beach is the most important nesting site that we work in the Caribbean," a researcher wrote in the email.