Wild Side: Stranded leatherback

Leatherback turtle beached on Cape Poge yields useful information.

Karen Dourdeville, coordinator of Mass Audubon’s turtle-stranding program, scanning for a PIT tag, or microchip. — Matthew L. Pelikan

On Wednesday, Oct. 30, word of a dead leatherback turtle beached on Cape Poge turned up on social media. I was one of several who passed word of the find onto Massachusetts Audubon’s turtle-stranding program (bit.ly/MASeaTurtles), based at Wellfleet Bay Wildlife Sanctuary. Karen Dourdeville, the stranding program’s coordinator, eager to examine the turtle, caught a ferry early on Nov. 2, and I drove her to the site of the stranding near Chappy’s northernmost tip.
We found the turtle lying near the wrack line, its pale belly up and a great black-backed gull methodically working on a hole in the reptile’s leathery hide. Karen began her examination by taking some basic measurements: length of the shell was a little over four feet, which, combined with the football-size head, made the animal about five feet long in total length. Based on its length, tail length (short in females, longer in males), and its estimated weight while alive (about 500 pounds), Karen determined that the turtle was a young adult female: A small to middling individual in a species that may exceed seven feet in length and weigh three-quarters of a ton.
Running a scanning device, wrapped in a plastic bag to keep it clean, hard up against the skin of the animal, Karen checked for a PIT (“passive integrated transponder”) tag around the shoulder joints. Like microchips in pet animals, PIT tags give a reliable marker of identity to a specific animal. If this turtle had been tagged, perhaps on its breeding grounds, her recovery on the Vineyard would have been a useful data point for biologists trying to untangle the movements of this extraordinarily far-ranging species.
Karen also used a scalpel and pair of forceps to lift samples of muscle tissue from a small hole she cut in the hide. Stored in a vial of saline solution for later analysis, the samples might allow the turtle to be linked genetically to a particular breeding population.
Part of the purpose of Karen’s examination was to establish a cause of death. The leatherback, with a U.S. breeding population limited to small numbers nesting on a few Florida beaches, is on the federal endangered species list, and a full understanding of what kills them is critical to planning effective conservation. In this case, there was no mystery; the reptile succumbed to a catastrophic boat propeller strike, with the left hind flipper sheared off and a foot-long gash deep into the animal’s side.
Karen was not equipped to carry out a full necroscopy of the turtle, but she determined that a look under the hood would still yield useful information. With a practiced hand, a sharp fillet knife, and a little unskilled muscle power from me, she lifted away the plastron, or lower shell, to expose the inside of the body cavity.
One known source of mortality in leatherback turtles is obstruction of their digestive tracts by plastic. These turtles eat mainly jellyfish, feeding 24/7 if they can find the prey. Leatherbacks, Karen explained, have a very long esophagus, which they’ll pack with prey if they’re feeding successfully. A plastic bag or balloon in the water looks enough like a jellyfish for turtles to ingest them.
The esophagus is lined with hollow, backward-pointing spines, which trap the jellyfish as the turtle expels seawater it swallowed. An indigestible plastic bag, once snagged in that phalanx of spines, is never coming out, and the resulting obstruction can be fatal. In this case, though, no plastic was evident (nor any jellyfish, either; the turtle had either not been feeding successfully before it was hit, or it lingered long enough after the strike for its digestive tract to empty).
Leatherbacks, the largest sea turtle species, live in oceans around the globe. They are supremely adapted to life in the ocean, with powerful flippers driving their vast but streamlined bodies as fast, by some accounts, as 20 miles per hour (though they typically cruise at a walking pace).
The Atlantic population ranges widely in search of prey, to latitudes as high as northern Europe and the southern tip of Africa. Their habit of swimming almost constantly in pursuit of prey may help them tolerate cold water, with heat generated by muscular activity keeping the animal warm. Leatherbacks can be common during the warmer months in the waters off Martha’s Vineyard (visit seaturtlesightings.org to see a map of sightings). Regrettably, this brings them close to a lot of fast-moving powerboats and floating balloons.
Nesting by this species is limited to a small number of suitable beaches, featuring low gradients (so the bulky animals can heave themselves ashore to lay eggs) and, usually, an absence of coral or rocks (presumably so this soft-skinned turtle can avoid injury as it comes ashore). The bulk of the western Atlantic population nests on the northern coast of South America, or on a handful of Caribbean islands. Africa also hosts a large breeding population, and the degree of connection between eastern and western Atlantic populations is one of the mysteries researchers are trying to resolve. In addition to mortality from boat strikes and plastic ingestion, leatherbacks suffer from egg poaching and loss of their limited breeding beaches due to human activity.
The experience was a complex one for me. On the one hand, I was fascinated to get an intimate tour from an expert of such a magnificent creature, even a decayed one. And as a naturalist, I’m at home with the cycle of life: This turtle was already a resource for the gulls and several species of flies. But I was also deeply, unscientifically saddened by the premature death, after years and thousands of miles traveled, of such a rare and impressive animal.