Sea Turtles on Cape Cod

Mass Audubon staff member examining a sea turtle © Esther Horvath

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When most people think of sea turtles, they imagine these marine reptiles enjoying the warm waters of the tropics. However, visitors and residents of the Cape may not realize that each summer hundreds of these turtles make their way into Cape Cod Bay!

While sea turtles don’t nest north of the Carolinas, many juvenile sea turtles spend their summers in the Bay, feeding on the plentiful crabs, jellyfish, and algae. Sea turtles are difficult to spot, though boaters may be lucky enough to see a sea turtle come up to the surface for a breath of air. While unlikely, it is possible to find five species of sea turtles in Cape Cod:

• Kemp’s ridley: both the smallest and most endangered sea turtle in the world. Ironically, it is also the most common turtle to strand on bayside beaches each winter. Juvenile ridleys are typically only five to ten pounds, but adults can grow up to 100 pounds. Several hundred typically strand each winter on Cape Cod in recent years.
• The loggerhead has the largest geographic distribution of any sea turtle in the world. Similar to the green turtle, the loggerhead is endangered and is also becoming a commonly stranding species. Juvenile loggerheads are large, between thirty and two hundred pounds, and adults can exceed 400 pounds. In recent years, two to three dozen loggerheads have stranded annually, with a high of nearly 150 in 2012.
• Green turtle: named for the green color of its body fat. It, too, is endangered, and has begun stranding in increasing numbers during the winter months, up to a few dozen per year in the past few years. Juveniles can weigh anywhere from five to twenty-five pounds, and adults can reach an impressive 400 pounds.
• The leatherback is the largest turtle species and heaviest reptile in the world. It is also the only sea turtle that can regulate its body temperature internally, unlike most reptiles that rely on their external environment for warmth. As such, leatherbacks do not cold stun, but unfortunately can be killed by boat strikes, fishing gear entanglement, and ingestion of plastic. Adult leatherbacks can reach up to eight feet long and weigh 1,500 pounds!
• The hawksbill is the least common sea turtle found near Cape Cod, with only one or two records of cold-stunned individuals. Like the Kemp’s ridley, it is critically endangered, but rarely leaves tropical water. Adults can reach up to 180 pounds.
• Hybrids: Kemp’s ridley, loggerheads, greens, and hawksbills will all hybridize with each other on occasion, and several hybrids have been found cold stunned. Careful scrutiny of scute pattern is required to identify a hybrid as such, and genetic testing is necessary to determine the parent species with certainty.

Cold-Stunned Sea Turtles

Most sea turtles (aside from the leatherback) are ectothermic, meaning that their body temperature is regulated by the temperature of the water around them. As winter approaches, the water of Cape Cod Bay slowly decreases, and sea turtles should make their way south to warmer tropical waters. However, each year since the late 1970s, some number of juvenile turtles does not make the journey in time. Trapped by the hook of the Cape, the turtles become disoriented. When the water reaches about 50° by mid-November, the turtles are too cold to eat, drink, or swim, and become “cold-stunned.”

Unable to move, these turtles are at the mercy of the winds and currents. When strong winds blow in from the north or west, the turtles can be pushed up onto the beach and left behind by the receding tide. However, these cold stunned turtles are lucky: since 1979, Wellfleet Bay staff and a corps of over 250 volunteers have patrolled the beaches of Cape Cod, on the lookout for cold-stunned turtles, which are rapidly transported to the New England Aquarium for evaluation and rehabilitation.

Summer Sightings

For boaters, if you see a sea turtle during the summer, please report it to SeaTurtleSightings.org.

Take Action

If you are interested in volunteering with the sea turtle stranding rescue, or in donating supplies or funds to the program, please call us at 508-349-2615.