• by Dr. Sarah D. Oktay, Managing Director UMass Boston Nantucket Field Station •
Long considered an amazing boon to sailors when found at sea on long voyages, the sea turtle today enjoys protected status in all the oceans. Right now a massive (6-8 foot long) deceased leatherback sea turtle carcass is circling the island. What happened to it is anyone’s guess. Just a few weeks ago, Robert Kennedy Jr. and his brother Max rescued a large leatherback sea turtle in Nantucket Sound that was wrapped in a buoy. The video of their feat as distributed by the Cape Cod Times can be found here: http://www.youtube.com/watch?feature=player_embedded&v=XhqHHvl6Owo. This large leatherback probably weighed 500 pounds. The National Ocean and Atmospheric Administration (NOAA) wisely did not fine the two men for accidentally violating the Endangered Species Act by releasing and most likely saving the turtle. If you see an entangled turtle you should call in the entanglement quickly (number at the end of the article) so that professional disentanglement crews can go to work. Every few years, experts such as Brian Sharp, stranding coordinator for the International Fund for Animal Welfare (IFAW) come to the island to give advice and training to our Marine Department and the Coast Guard on disentanglement procedures. Last year in early October a large leatherback was found stranded on lthe beach near Truro which is very rare and rescued and rehabilitated with the help of the IFAW crew and the New England Aquarium (NEAQ). I was teased for my over use of acronyms the other day and now you know why.
Sea turtles are one of the Earth’s most ancient creatures. The seven species found today became distinct from all other turtles at least 110 million years ago. The extinct sea turtle Archelon was one of the largest sea turtles that ever lived. It reached a length of 3 to 4 meters, resembled our modern day leatherbacks and lived 85-65 million years ago (late Cretaceous). Sea turtles are classified in the Class Reptilia, Subclass Anapsida and Order Chelonii. There are seven recognized species of sea turtles, six of which are in the Family Cheloniidae (the hawksbill, green, flatback, loggerhead, Kemp’s ridley and Olive ridley turtles), with only one (the leatherback or Dermochelys coriacea) in the family Dermochelyidae. All seven species are either endangered and on the verge of extinction, or threatened to become endangered under the U.S. Endangered Species Act. Threats to sea turtles today include the harvesting of their eggs for human consumption, entanglement and entrapment in fishing gear, ingestion of litter especially plastics, and coastal development. Around Nantucket, we are most likely to encounter leatherbacks and loggerhead sea turtles although green and Kemp’s ridleys are also found in the Atlantic.
Sea turtles are reptiles and are ectothermic, otherwise known as “cold blooded” which means they cannot regulate their own body temperature. As a result, we sometimes get cold stunned turtles that have traveled up to Massachusetts in the relatively warm Gulf Stream and then become sluggish in the chilly temperatures of our waters. This occurs most often in the fall. Only the leatherbacks have adapted to cold temperatures. Leatherbacks swimming off of Canada have body temperatures of close to 70 degrees Fahrenheit when the surrounding water is 40 degrees. They could almost be considered warm blooded if they controlled their body temperature through metabolic processes but instead they use a variety of techniques and physical adaptations similar to other marine mammals to help their large bodies absorb and retain heat. They have thick layers of fat and a tendency to stay in warmer currents to keep their temperature high. In addition, leatherback arteries and veins in their flippers are close together to transmit heat quickly and they can restrict blood flow to their extremities in colder waters. The most interesting fact I found in my research for this article was that leatherback turtles practice Lamaze breathing techniques during egg laying to reduce the amount of air that enters the lungs and prevent hyperventilation. No research indicates that the males coach them in Lamaze classes.
Leatherbacks start appearing in larger numbers in the late summer and fall in the Nantucket Sound. They are chasing one of their favorite foods, jellyfish. As the water warm up in August, the populations of moon jellies, sea nettles and the bioluminescent ctenophores (more commonly known as comb jellies , and not actually jellyfish) increase and leatherbacks enter the area in greater numbers to feed. The Large Pelagic Research Center (LRPC more at http://www.tunalab.org/leatherback_turtles.htm retrieved September 15, 2013) is a good source of information on leatherbacks. They have been tagging and researching leatherbacks with assistance from the Provincetown Center for Coastal Studies. These creatures usually stay a fair distance offshore so tagging them and tracking them as they forage and migrate is essential to understanding their habitat needs and what problems they may face in a warming world. LPRC researchers analyze basic elemental stable isotopes such as carbon and nitrogen that vary depending on the trophic level of the prey in leatherback tissues and prey to improve our understanding of the leatherback’s diet and energy sources. Isotope analyses are particularly helpful for discerning diet for periods of time when animals can’t be observed, and for detecting prey that are rapidly digested. Stomach samples from deceased turtles often don’t tell the whole story, because only harder parts may still be in the gut, or because the animal has some type of issues with starvation or food acquiring that led to its demise. Propeller strikes by recreational boaters are the most common cause of mortality to leatherback turtles around the Cape. For example, in 2011, a large 440 pound leatherback was found dead near Falmouth with multiple propeller strike marks.
The leatherback has several characteristics that distinguish it from other sea turtles. It is the largest sea turtle and one of the largest reptiles only surpassed by three species of crocodiles. Its most notable feature is the lack of a bony carapace. Instead of scutes (those plates of bone typical on aquatic turtles), it has thick, leathery skin with embedded minuscule osteoderms, which is a pseudo bony deposit you might recognize more in a crocodile or armadillo. Seven distinct ridges rise from the carapace (turtles back plate), forming lines over the top from front to back. The entire turtle’s dorsal surface is colored dark grey to black, with a scattering of white blotches and spots. Demonstrating countershading (dark on top light underneath) like many fish species, the turtle’s underside is lightly colored. Instead of teeth, the leatherback turtle has points on the beak of its upper lip, with backwards spines in its throat to help it swallow food and to stop its prey escaping once caught.
Leatherbacks start as hatchling on far southern beaches down in Florida, in Central America and the French Guyana and other locations in South America. Before they hatch from eggs they are prey to raccoons, seagulls, large crabs, dogs, coyotes, and monitor lizards and as hatchlings they may be picked off by larger raptors and shorebirds before the reach the ocean. In the ocean large fish, octopi, and requiem sharks may feed on them before they get too big, As adults, they don’t suffer from too predation except for the occasional orca, great white shark or tiger shark attack. They are very aggressive when attacked (like most of us). They are epic migraters swimming further than any other species of turtle and have been known to cross the Atlantic and of course every year travel from as far north as the Labrador Sea (even in some cases the Arctic) where they feed in the summer to very far down the coast of South America to breed and lay their eggs. Very little is known about leatherback mating except for the fact that we know they do it in the ocean away off shore. Perhaps they are shy, or sick of being followed by scientists.
Except for the occasional and sometime deadly knock to the noggin by a boat, sea turtles are very well adapted to their solitary lives at sea. The shells are amazingly strong, with a thick carapace on top and the plastron protecting their belly. Sea turtles can only partially retract their flippers and head, unlike their terrestrial cousins who can completely withdraw. Leatherbacks can’t retract their flippers at all. As a result, sea turtles are susceptible to shark bites and attacks on their appendages. At the turtle rehabilitation facility and Kemp’s Ridley hatchery in Galveston, I have seen 40-year-old loggerheads with giant gaping shark bite wounds that have lived to tell their tale. Like manatees, sea turtles are relatively slow moving and can be hit by boats when they are at the surface taking a breath. A resting sea turtle can stay underwater for 4-7 hours. Leatherbacks can dive to a depth of more than 1,000 meters (3,000 feet) in search of their prey. The hard-shelled species like the loggerheads dive at shallower depths. The leatherback is adapted to deep dives because of its unique morphology. Unlike other sea turtles, the leatherback lacks a rigid breastbone that allows it to collapse during deep dives. They store a large amount of oil in the skin which acts as a shock absorber, and the leathery shell absorbs nitrogen, reducing problems arising from decompression (what we call “the bends” or rapid expansion of air bubbles) during deep dives and resurfacing.
Sea turtles have strong, stiff fore flippers which pull them through the water while their hind flippers steer. Their large eyes have adapted to gather light in the light-limited depths of the ocean. Their nostrils are placed high on the tips of their beaks so they can catch a breath quickly at the surface. They can hold their breath for several hours, but on average come up to the surface every thirty minutes to breathe. Adult sea turtles can weigh from 150 pounds for a typical adult green turtle to 2,000 pounds or more for the gargantuan leatherbacks. I have seen a 1,000 pound leatherback that precisely fit into the bed of a half-ton pickup truck cementing the “truth in advertising” motto in my head. Their predilection for jellyfish has cause them to significantly suffer from plastic bag ingestion, which is one of the reasons that international maritime law currently forbids disposal of plastics at sea. Plastic consumed by turtles leads to partial or complete obstruction of gastrointestinal tract. While the plastic takes its toll on the turtle’s diet, energy, and reproduction, a complete blockage can lead to starvation. The more plastic a turtle ingests the more likely the trash will kill it, but even a little plastic can weaken a turtle significantly.
Most sea turtle hatchlings use moonlight to find the ocean after they emerge from their shells buried deep in the sand. The presence of lights from cars or oceanfront development can confuse the hatchlings and cause them to rush in the opposite direction. Gear entanglement is a serious problem for sea turtles and many different devices have been invented to help turtles escape shrimp and other dragger nets. These boxes are trap door type devices that allow the turtles to pop out of the nets while retaining the shrimp or fish inside. As air breathers, turtles can be drowned if they are ensnared by bottom trawling nets. The type of device used in shrimper nets is called a TED, or turtle excluder device. U.S. Law requires that all shrimp imported to the U.S. or caught and sold here is harvested by boats using TEDs. In the Atlantic fishing area, various fishermen and agencies are experimenting with “breakaway” nets that will release if a large turtle, dolphin or shark is entrained while hanging onto the fish they are trying to catch.
Locally, in addition to research conducted by biologists at the New England Aquarium, the Provincetown Center for Coastal Studies monitors and assists in strandings and entanglements of sea turtles in Massachusetts waters (www.coastalstudies.org/what-we-do/stellwagen-bank/turtles.htm). If you see an entangled turtle you should call the Marine Animal Entanglement Hotline at 1-800-900-3622 or contact the US Coast Guard on VHF channel 16. According to the PCCS web site “if you do come across a sea turtle on beaches along the Massachusetts southeast coast you should cover the individual with sea weed or beach grass, mark the spot with something prominent and contact the Massachusetts Audubon Society in Wellfleet, on Cape Cod at 508-349-2615 or, for other regions of Massachusetts, the New England Aquarium in Boston”.
Portion of this article appeared in September 10, 2009 issue of Yesterday’s Island which can be found at http://www.yesterdaysisland.com/archives/science/19.php. That article goes into greater depth on Loggerhead turtles that we also occasionally see around the island. They are swept up here often on the Gulf Stream and can often e cold-stunned.
To learn more about the Kennedy sea turtle rescue this summer go to http://www.nydailynews.com/news/politics/kennedy-brothers-rescue-sea-turtle-article-1.1402420 retrieved September 14th, 2013. NOAA has a “How to save Sea Turtles Guide” that can be found at http://www.turtlenests.org/pdf/HelpSeaTheSeaTurtle-BeachgoersGuide.pdf retrieved September 15, 2013. Information for this article came from “Sea turtles: a complete guide to their biology, behavior, and conservation” by James R. Spotila and from various web sites listed above in the text. To find out more about recent stranding in Massachusetts, explore: http://www.massaudubon.org/Nature_Connection/Sanctuaries/Wellfleet/seaturtles.php