As morning light spread across Nantucket Sound on Wednesday, staff from the New England Aquarium released 17 endangered and threatened sea turtles back into the ocean after months of medical care.
The release, held at West Dennis Beach after ocean temperatures crossed the 65-degree threshold, marked the first of the season for the Aquarium’s Sea Turtle Hospital in Quincy — and a high point in what has become an increasingly urgent cycle of rescue and rehabilitation.
Each winter, hundreds of sea turtles wash ashore on Cape Cod, cold-stunned by frigid water that leaves them unable to move or feed. This stranding season, 518 turtles were rescued between November and January — tied for the third busiest season on record. Fifteen years ago, it was common to see only about 100 strandings, but as ocean temperatures rise and more turtles stray north into New England waters, the average number has more than quintupled.
“Cold-stunning is basically hypothermia for turtles,” said Adam Kennedy, the Aquarium’s director of rescue and rehabilitation. “They can’t regulate their body temperature, so as the water gets colder, they float to the surface, and the wind blows them in.”
The phenomenon has worsened as the Gulf of Maine, one of the fastest-warming ocean bodies on Earth, continues to heat rapidly due to human-caused climate change. Warmer waters draw more turtles north each summer, but when fall arrives, their instinct to migrate south kicks in. Guided by Earth’s magnetic field, they attempt to navigate back — only to become trapped by the hook-shaped geography of Cape Cod, which blocks their path and strands them in dangerously cold waters.
Most suffer from malnourishment, pneumonia, and other trauma after spending days or weeks adrift.
“You’re bringing these turtles in from the winter, where they’re kind of on death’s doorstep,” Kennedy said. “To this point where they look wonderful, they look great — and they’re ready to go.”
Biologist Amanda Alig introduced Graeae, a Kemp’s ridley sea turtle, to the crowd before releasing it in Dennis.Craig F. Walker/Globe Staff
Among those released was Tyche, a critically endangered Kemp’s ridley sea turtle with a serious facial injury.
“Not knowing if it could even open its mouth enough to eat — or whether it would be able to thrive — that was a big question when the turtle first arrived,” Kennedy said. “We had to ask ourselves: Do you euthanize a turtle like that, or give it time?”
The staff waited. Over the months, Tyche healed. Her story — documented by the Aquarium’s team — went viral on social media. Kennedy said he was thrilled by the public’s response and proud of his team’s work.
Named after the Greek goddess of luck and fortune, Tyche was one of several turtles this season named under a mythology theme. Others released this week included Selene, Oceanus, Athena, and Pan — names that reflect each animal’s journey.
Helen, a loggerhead sea turtle, headed towards the water after being released at West Dennis Beach.Craig F. Walker/Globe Staff
Ten turtles were fitted with satellite tags, and eight of those also received longer-lasting acoustic tags.
Kara Dodge, a research scientist at the New England Aquarium, said satellite tags transmit real-time data when turtles surface to breathe, while acoustic tags work underwater but only near fixed receivers. Acoustic tags can last up to ten years, compared to six to twelve months for satellite tags.
Dodge said researchers use the tags to better understand what happens to turtles once they’re released.
“Are they surviving? Are they reintegrating with the wild population? Are they doing ‘normal turtle things’?” she said.
The 17 released this week are just the beginning. Twenty-five more remain in rehabilitation and will hopefully all be cleared for release later this summer.
“All the releases feel amazing,” Dodge said. “It’s just the culmination of so much work, and having them back in fantastic health and ready to go — it’s pretty much thrilling every single time.”
With a satellite tag attached to its shell, Oceanus headed out to sea after being released in Dennis.Craig F. Walker/Globe Staff
Nathan Metcalf can be reached at nathan.metcalf@globe.com. Follow him on Instagram @natpat_123.