posted September 24, 2012 05:20 PM            

The 655-pound turtle was rescued on Wednesday evening after he was found stranded on a mud flat in Pamet Harbor in Truro, Mass., according to the New England Aquarium.

The black, male, leatherback turtle came in "near death" on Thursday, and medical professionals treated him with a variety of medications to help stabilize his blood valves and oxygen levels, the New England Aquarium notes. Even at 655 pounds, the turtle is considered underweight; adult turtles can weigh more than 1,000 pounds.

“We are crossing our fingers and will do everything we can do to keep it alive,” the aquarium’s Tony LaCasse told ABC News when the animal was first recused. “The feeling is to view a live leatherback up close is such a rare opportunity. The staff are keen to work with such an animal.” Doctors said the turtle was at least 25 to 30 years old, according to ABC.

On Saturday, the turtle was released back into the wild from the back of a fishing boat positioned a couple of miles off of Harwichport.

When the 655-pound turtle was found, rescuers noticed a straight line of damaged tissue on his flipper. The injury, which hindered the turtle's ability to search for food, could have been caused by entanglement in a vertical line, according to ABC News.

Leatherbacks cannot be kept in captivity, the New England Aquarium explains:

Unlike other sea turtle species, leatherbacks have never been displayed in aquariums given their massive size, their constant swimming into tank walls and their exclusive diet of sea jellies (jellyfish). These endangered giants rarely strand alive and have usually survived for just a couple of days in an aquarium setting. Although this leatherback was not in ideal condition, Aquarium officials decided that the animal’s best chance of survival was back in the sea with its blood values stabilized and energy restored.

Leatherback turtles are the largest turtles on Earth, according to National Geographic. They are the only remaining representatives of a family of turtles whose evolutionary path dates back more than 100 million years.

Although leatherback numbers are stable or increasing in the Atlantic, the population in the Pacific has declined sharply. Eggs are often taken from nests and consumed for subsistence or as aphrodisiacs, National Geographic reports. Threats to the population include fishing lines and nets as well as boats. The turtles also are known to ingest floating plastic debris they mistake for jellyfish.

Leatherback turtles were listed as endangered under the Endangered Species Act in 1970. The National Oceanic and Atmospheric has attempted to minimize the interaction between turtles and trawl gear, as well as design habitats specifically for the animal.