A 655-pound leatherback sea turtle is being treated by England Aquarium staff after being found stranded and injured on a mud flat in Truro.

Staff from the Massachusetts Audubon Sanctuary at Wellfleet Bay contacted the aquarium after locating the turtle at dusk on Wednesday. Rescue efforts were postponed until Thursday morning due to the location, darkness, and incoming tide. The turtle was transported to the aquarium’s Marine Animal Care Center in Quincy.

Medical staff noted that about 40 percent of the turtle’s front left flipper was gone due to recent trauma. Leatherbacks, who use their large front flippers to pull their bodies through the water, often lose parts of them to sharks or other large predatory fish and can still survive.

Advertisement - Continue Reading Below

Rescuers have started administering drugs to treat the turtle for dehydration, trauma, and shock. Although its heavy weight may come as a surprise to many, the 7-foot turtle is actually considered underweight. Adult leatherback turtles typically weigh around 1,000 pounds, said aquarium spokesman Tony LaCasse.

These endangered sea turtles are rarely found alive after stranding, and the aquarium has only handled five leatherbacks from Massachusetts beaches in more than 40 years, the aquarium said in a statement.

The aquarium said the animal’s prognosis is poor, since in order to strand it had to become critically ill, but aquarium veterinarians and biologists are working to rehabilitate the sea giant.

Leatherbacks usually migrate north to the area in June to feed on jellyfish and return south during the months of September and October, the aquarium said.