A nearly half-ton leatherback sea turtle carcass washed ashore on Martha’s Vineyard on June 16, marking the first sea turtle casualty of the summer and serving as a timely reminder for boaters to be on alert as the protected animals return to local waters.
The mature female turtle, weighing in at 700 pounds, was found in unusually “fresh” condition at Red Beach in Aquinnah, according to Karen Dourdeville, sea turtle research coordinator at Mass Audubon Wellflleet Bay Wildlife Sanctuary. A necropsy revealed no signs of a vessel strike or entanglement injuries.
Dr. Charles Innis, senior scientist and veterinarian at the New England Aquarium’s Anderson Cabot Center for Ocean Life, conducted the necropsy with help from the Aquinnah Environmental Lab, the state Environmental Police and the Chilmark harbormaster’s office.
It’s not known how old the turtle was, but she wasn’t a juvenile.
“It’s difficult to age sea turtles,” Dourdeville said.The turtle’s curved carapace, or upper shell, measured 155 centimeters and “in leatherbacks any curve carapace length over 145 centimeters is considered sexually mature,” she said.
The turtles mature at 15 to 20 years old, she said, “so she was at least older than 15.” Estimates of leatherback life spans range from 45 to 60 years.
While the turtle showed no outward injuries, vessel strikes are a common cause of injury and death for sea turtles in the region. Four species of federally protected sea turtles — loggerhead, Kemp’s ridley, green and leatherback — feed in local waters during the summer, she said.
Leatherbacks are also listed as endangered in Massachusetts and as a “species of greatest conservation need” in the Massachusetts State Wildlife Action Plan.
This 700-pound leatherback sea turtle carcass was found on a Martha’s Vineyard beach on June 16. The female turtle was likely at least older than 15 years, scientists said.
A significant loss for an endangered species
“The loss of any reproductive female is significant to an endangered population,” Dourdeville said.
During a nesting season, she said, a female leatherback may dig from four to seven nests about 10 days apart, laying 55 to 95 eggs in each on tropical and subtropical beaches.
“Each nesting season is energetically very expensive for a female leatherback, so she will nest only every two to three years,” she said. “The fact that this stranded female leatherback in Aquinnah was in our northern waters to forage meant that this was one of her non-nesting years.”
Leatherbacks are regular visitors to New England waters
Once considered rare visitors, leatherbacks are now known to migrate to New England regularly in search of their primary food source, jellyfish — which have also boomed in local waters in recent years, with some species more commonly found farther south now showing up off Cape Cod’s south coast. According to MassFisheries, leatherbacks are the largest living turtle species.
The turtle’s remains, Dourdeville explained, were notably well-preserved.
The typical summer or early fall sea turtle stranded carcasses are more decomposed, often exhibiting fatal vessel-strike wounds, she said. “These would have floated longer before washing ashore, with warmer air and water temperatures hastening decomposition.”
In cases of vessel strikes, the carapace is typically cut open, exposing the body to seawater and scavengers, also increasing the rate of decomposition.
“The Aquinnah leatherback was likely not dead more than a couple of days before washing onto the beach,” she said.
The cause of death remains under investigation. Dourdeville said tissue samples will be sent to Brian Stacy, a veterinary medical officer for the National Oceanic and Atmospheric Administration’s National Sea Turtle Program within the Office of Protected Resources.
The turtle’s remains were buried on Aquinnah Wampanoag tribal land, she said.
Vessel strikes, entanglements not the only threats
Dourdeville urges boaters to be on watch for returning turtles, which are particularly vulnerable as people also increase their water activities. In the summer and early fall of 2024, a total of 34 dead sea turtles were reported in the region, including six leatherbacks, 23 loggerheads and five Kemp’s ridleys.
Threats go beyond collisions and entanglements, she said.
“Plastics in the ocean are an increasing concern for sea turtles — both microplastics and macro (visible) plastics,” she said. “Leatherbacks can mistake a floating plastic bag for a jellyfish, their prey.”
Climate change is also affecting sea turtles in many ways, she added.
“One big concern caused by climate change isn’t in our area, but rather on nesting beaches. Some nesting beaches in the tropics and subtropics are seeing increased erosion, so less area for nesting,” Dourdeville said, “and the hotter sands affect both sex ratio of hatchlings and hatching success rates.”
Tracking and protecting sea turtles
NOAA and the U.S. Fish and Wildlife Service have not issued recent turtle-specific alerts for New England, but Mass Audubon identifies “hotspots” — areas where multiple leatherbacks are repeatedly sighted over several days, often due to jellyfish aggregations, Dourdeville said. In such cases, NOAA can ask the U.S. Coast Guard to issue a warning to boaters.
Currently, there are no vessel speed regulations in place for sea turtle feeding areas, unlike those in place for whales.
How to help
Boaters are encouraged to report any sea turtle sightings to seaturtlesightings.org or by calling 888-732-8878. These reports should include details such as date, location, and species identification.
Mass Audubon’s sea turtle work is conducted under a U.S. Fish and Wildlife Service permit. Its Wellfleet Bay staff are federally permitted responders for sea turtle strandings in southeastern Massachusetts.
Heather McCarron writes about climate change, environment, energy, science and the natural world, in addition to news and features in Barnstable and Brewster. Reach her at hmccarron@capecodonline.com.
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This article originally appeared on Cape Cod Times: First sea turtle death of summer signals need for care: Mass Audubon