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Science
Volume 39 Issue 19 • Sept 10-16, 2009
now in our 39th season

Sea Turtles

by Dr. Sarah D. Oktay
Managing Director UMass Boston Nantucket Field Station

I had every intention of writing about erosion, algae, and particle dynamics for this week's article, as I promised in last week's article on pollen. Then a phone call came in from Edie Ray with the Nantucket Marine Mammal Stranding Team (www.nantucketstrandingteam.org) concerning a deceased loggerhead turtle sighted at Jetties Beach.  I have been on the stranding team for several years.  During the summer I am usually too busy to help out much, but a Labor Day three-day weekend and the slowdown that occurs this time of year allowed me to respond to the call.  As a result, a large stinky turtle is in the Nantucket Field Station freezer in place of much more desirable ice cream, and I feel obligated to change my topic this week and discuss the biological flotsam washing up on our shores.  For some reason, holidays tend to be busy times for marine mammal stranding incidents, probably due to the fact that more people are enjoying the local waters and therefore, there are more eyes around to spot stranded animals.  For instance, Saturday, Sept 5, the stranding team had three separate calls regarding gray seals including a possible boat strike with a propeller injury on a large gray seal off Great Point.

The previous week had been an extremely exciting week for marine biology fans: a leatherback turtle was reported near Great Point entangled in a small yellow and white buoy; great white sharks have been spotted off Monomoy Beach in Cape Cod and were successfully tagged; and a large porbeagle that may break the current state record of 455 pounds was caught in a local shark fishing tournament.  After the multiple seal calls on Saturday, Sunday's “catch of the day” was a recently deceased adult loggerhead turtle. This turtle was bobbing against the east side of the East Jetty, demonstrating particle physics on a large scale.  Very recently dead and in relatively good shape (except for being dead), the loggerhead was about 35-40 pounds and approximately three feet long and two feet across, including its flippers.  I used a technique honed from working with turtles down in Galveston for several years for locating the turtle after we had questioned beach goers regarding its location: they smell amazingly putrid when dead, rivaling the stench of any other dead creature.  As they decompose, gases build up in their bodies which cannot escape easily around their thick shells and they become sad, buoyant, balloon-like corpses. Surprisingly, this escaped the notice of people enjoying the beach only 100 feet away.

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, 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 who 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.

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 fliers and head, unlike their terrestrial cousins who can completely withdraw.  As a results, 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 who 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, jellyfish. 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. 

Despite these adaptations, sea turtles, like seals, must come ashore to lay their eggs which need warmth to develop.  And like whales, their feeding grounds are often at great distances from their breeding grounds.  Females will migrate hundreds, even in some cases, thousands of miles to the beach where they were born to lay their eggs.  There is growing evidence that long distance migrations may be guided by magnetic cues.  Loggerheads are the supreme travelers of the marine world and young loggerheads cover 9,000 miles in their first few years.  To learn more about these amazing journeys and see how scientists test their reactions to magnetism, visit: http://www.unc.edu/depts/oceanweb/turtles/.

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 who precisely fit into the bed of a half-ton pickup truck cementing the “truth in advertising” motto in my head.  Sea turtles can live up to 80 years.  They eat plants, jellyfish, shrimp, and clams.  They really like jelly fish and have suffered from plastic bag ingestion for many years as a result of the similarities between these bags and jellyfish, 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.

This slide show found at http://lee.ifas.ufl.edu/FYN/FYNPubs/TheDangersofPlasticBags.pdf (access Sept 6, 2009) is a good, although heartbreaking, primer on the hazards of plastic bags in the marine food chain.  Nantucket should do more to publicize our successful elimination of plastic bags in retail stores.  Scientists at the University of Southern Mississippi may have found a way to reduce the amount of plastics in the ocean.  They’ve invented a line of plastics that dissolve in seawater.  The new plastics are made of polyurethane that’s been modified with polylactic-co-glycolic acid, a polymer used in surgical sutures.  This material is currently being tested in navy and academic labs.  The Navy is funding this project because of the significant amount of fuel expended while hauling around all the plastic used on board.

Loggerhead turtles (Caretta Caretta) are the most common of all the species of sea turtles and they are simply listed as threatened, not endangered.  The genus name "Caretta" is a latinization of the French word "caret," meaning “a kind of turtle.”  From http://www.turtles.org/loggerd.htm we learn that they have reddish brown carapaces with a light orange or yellow plastron and very large heads.  Loggerhead turtles can be 3.5 feet long and weigh up to 400 pounds.  They feed on crabs, mollusks, and jellyfish and use their powerful jaws to crash crabs as large as horseshoe crabs.  The average carapace length is about 92 cm (about 36 inches or one yard) and average body mass about 113 kg (250 pounds).

Like many turtles, Caretta caretta exhibits temperature-dependent sex determination (TSD).  The sex of hatchlings is determined by egg temperature during the middle third of incubation.  The pivotal temperature—the temperature at which an 50:50 ratio of males:females is produced—varies from location to location around the world.  Generally, the pivotal temperature is between 28 and 30 ºC. Temperatures of 24 to 26 ºC tend to produce all males and temperatures of 32 to 34 ºC tend to produce all females.  Hatchlings can vary in color from light to dark brown.  Flippers are dark brown with white margins.  It is assumed that hatchlings live out their "lost years" in rafts of sargassum and/or debris in open ocean drift lines.  They remain part of this drifting community and grow to 40 or 50 cm carapace length.  They then migrate to the shallower coastal waters which become their foraging habitat.

There are no visible external differences between males and females until they reach adulthood.  The tail and the size of claws are the only discriminating features between adult male sea turtles and adult females.  All juveniles, male or female, have a short tail and short claws that are just visible at the leading edge of the front and hind flippers.  However, as the male reaches adulthood, his tail will grow so that it extends well past the end of the shell, and his claws become long and hooked.  Adult females, like juvenile sea turtles, have a short tail, and small claws.  According to Wikipedia: “Loggerhead turtles are the most common sea turtle to nest in the United States.  Loggerheads nest from Texas to North Carolina, requiring soft sandy beaches, where there is little light pollution; with the largest concentration of nests in south Florida.” (http://en.wikipedia.org/wiki/Loggerhead_Sea_Turtle; accessed Sept 6, 2009).  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.  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.

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 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. To learn more about these devices, go to: http://en.wikipedia.org/wiki/Turtle_excluder_device.

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). This past week, Nantucket stranding team members were assisted by the New England Aquarium, the Trustees of the Reservation, Massachusetts Audubon (Wellfleet), the U.S. Coast Guard, and our new Environmental Police Officer, Keith Robinson.  We are extremely fortunate to have a well trained team and responsive and cooperative partners.

To report a stranded or entangled animal on Nantucket, please call 508-228-1212; the officer on duty will route your information to the Marine Department and the Stranding Team.  In other parts of Massachusetts, 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”. Information on the Nantucket Marine Mammal Stranding Team can be found at www.nantucketstrandingteam.org.

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. I would also recommend the site http://www.turtles.org/summer/ which is a  fun and informative blog about “honus”, Hawaiian for sea turtles.  To find out more about the Kemp's Ridley sea turtle head start program and see the lab I worked in on Galveston Island, go to http://galveston.ssp.nmfs.gov/seaturtles/.  To find out more about recent stranding in Massachusetts, explore: http://www.massaudubon.org/Nature_Connection/Sanctuaries/Wellfleet/seaturtles.php

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