3 dead leatherbacks found on Cape show signs of entanglement

By Kristen Young
Posted Oct 9, 2019

Turtles found along Cape Cod Bay beaches over 10 days.

DENNIS — A leatherback turtle that washed up in Sesuit Harbor on Monday is the third to be found dead along the Cape Cod Bay shoreline in about a week and a half.

“We know there have been more of them this year in Cape Cod Bay than in Nantucket Sound and Vineyard Sound,” Karen Dourdeville, sea turtle stranding coordinator for the Massachusetts Audubon Society’s Wellfleet Bay Wildlife Sanctuary, said of the species.

The data is not scientific, but more leatherback sightings were reported by boaters in the bay this season than in prior seasons, when the sightings came primarily from Nantucket and Vineyard sounds, according to sanctuary staff.

The three leatherbacks, which are the world’s largest turtle species, were found on Cape Cod Bay beaches between Sept. 27 and Oct. 7. Each showed possible signs of entanglement in fishing or boating gear.

According to Robert Prescott, former longtime director of the sanctuary who continues to oversee turtle research, the leatherback found Monday was a juvenile male. Because it was fairly decomposed, it is impossible to know with certainty what caused the death, but wounds indicate that a line had been wound tightly around its left flipper, cutting into its flesh, Prescott said. The animal had likely became so severely entangled in the line that it drowned or died later from its injuries, he said.

The death of a leatherback found Sept. 29 on Breakwater Beach in Brewster was undoubtedly caused by entanglement, he said.

“It had tangled in chain that people use for winter moorings,” Prescott said. “That was an immature female, which was even more of a loss to the population.”

A leatherback found Sept. 27 on Bayview Beach in Dennis also showed signs of a potential entanglement, although the carcass was too decomposed for researchers to determine a cause of death.

“It too showed some scarring around the flipper where it meets the body,” Prescott said.

In total, six dead leatherbacks have washed ashore in Massachusetts since mid-September, a number that Prescott said is fairly typical for any given season.

Prescott described the species as world travelers. Atlantic leatherbacks migrate through local waters twice each year. The first pass happens in the spring, as the turtles travel from just north of the equator to waters around Greenland and Newfoundland. Traditionally, they have made their second pass through Cape waters in late August or early September as they return south.

“It’s just great feeding up here,” Prescott said. “It’s good water quality, lots of marine invertebrates. They do very well up here in the Northeast.”

But in recent years, the turtles’ migratory patterns have shifted.

“There have been some tagging studies showing that some leatherbacks have stayed in our waters for an extended period through the summer and then into the fall,” Dourdeville said.

Rapidly rising temperatures in the Gulf of Maine could have something to do with the change, according to Prescott. The turtles tend to head south when northern waters cool and their food sources — namely jellyfish — begin dying off.

“Years ago, that would have happened two to three weeks sooner,” Prescott said.

Now, the peak time for leatherback sightings in waters around the Cape begins in mid-September and lasts into October or sometimes even November.

According to Prescott, the later migration could actually be beneficial. Leatherback turtles regulate their own body temperature, so they don’t get cold-stunned as other sea turtles do. And, because boating activity tends to drop off in September and October, passing by the Cape later in the season could lessen the risk of ship strikes.

Boaters who spot a sea turtle can report it at seaturtlesightings.org. To report an injured, cold-stunned or entangled sea turtle, call 508-349-2615, ext. 6104.