Each summer, hundreds of sea turtles swim into Cape Cod Bay, which sits in the crook of an elbow-shaped peninsula on the East Coast. It’s a great foraging spot during the warm season, but when the weather turns, many of the reptiles struggle to make their way out of the hook-like bay, putting them at risk of getting shocked by the cold waters.
This problem primarily affects Kemp’s ridley sea turtles, the smallest and most endangered of all sea turtles. In recent years, several hundred of these critters have been stranding on Cape Cod each winter, cold, disoriented and in desperate need of help. Now, a study in PLOS One is offering new insight into the conditions that might be driving the turtles onto Massachusetts beaches.
Kemp’s ridley turtles once veered dangerously close to extinction, their numbers decimated by egg harvesting and commercial fishing nets, which entangled the turtles and caused them to drown. The Kemp’s ridley was listed under the under the U.S. Endangered Species Conservation Act, a precursor to the U.S. Endangered Species Act, in 1970. For a time, conservation measures—like the protection of nesting females and the relocation of nests to hatcheries—seemed to be working; by 2009, nesting Kemp’s ridley females numbered more than 21,000, up from around 200 in the 1980s.
But the turtles’ recovery has slowed in recent years, and strandings on Cape Cod have increased “by nearly an order of magnitude,” according to the study authors. One problem, reported Josh Wood of the Guardian last year, is that the Gulf of Maine, which spans from Cape Cod to Nova Scotia, is becoming unusually warm. This in turn draws more turtles into Cape Cod Bay, and encourages them to stay there for longer. But when cold weather hits, the unique topography of the Cape Cod peninsula proves to be a death trap.
“Cape Cod Bay we often call a deadly bucket,” Tony LaCasse, a spokesperson for the New England Aquarium, told Wood. The turtles would have to swim north and then east to get around the hook to warmer seas, but the cold northerly waters confuse them.
“[T]heir instinct tells them to retreat back into the shallow warmer water of the bay and wait it out,” LaCasse explains. “But the problem is it’s the end of the season and there’s no way to get out.”
Most sea turtles are ectothermic, meaning that the waters around them regulate their body temperature. Trapped in frigid temperatures, Kemp’s ridleys become “cold-stunned”—too cold to eat, drink or swim. Winds and currents carry them onto the beach, sometimes in droves. In 2014, for instance, 1,250 sea turtles washed ashore, some dead, others in need of emergency care.
James Manning, an oceanographer with the National Oceanic and Atmospheric Administration and co-author of the new report, tells Sabrina Imbler of Atlas Obscura that scientists did not have a clear sense of what part of the bay the turtles were coming from, or what temperatures triggered their shock. So the study authors used computational modelling to simulate ocean currents in Cape Cod Bay, and supplemented those results with data collected through drifters, or instruments that can be tracked via satellite. The team also looked at water temperature data and records of where Kemp’s ridley turtles had been found.
The results of this investigation suggested that Kemp’s ridleys are most likely to become stranded when water temperatures drop below 50.9 degrees Fahrenheit and, at the same time, wind stress is intense in certain directions. As the study authors point out, there is still much that remains unclear about the strandings—like the depth at which Kemp’s ridley turtles typically become hypothermic. But the researchers say their model can help predict the stranding locations of Kemp's ridley sea turtles on Cape Cod beaches,” which may in turn “guide search and rescue efforts in the future.”
Dedicated volunteers from the Mass Audubon’s Wellfleet Bay Wildlife Sanctuary are already working to rescue stranded sea turtles, patrolling Cape Cod’s beaches and, if the turtles are still alive, providing first aid and ushering them to the New England Aquarium’s Animal Care Center. According to Margaret Hetherman of the Washington Post, the turtles are assessed for hypothermia and related complications, like low blood sugar, pneumonia and a slow heart rate.
“Sometimes we are seeing a heartbeat of one beat per minute,” Connie Merigo, director of the Aquarium’s Rescue Rehab program, tells Hetherman. “But that animal is still alive and, with emergency care, can go on to survive and be released.”