Sea Turtles

Sea Turtles
Found these guys chowing down on some algae off the Port Aransas South Jetty.
A well-known scientist (some say it was Bertrand Russell) once gave a public lecture on astronomy. He described how the earth orbits around the sun and how the sun, in turn, orbits around the center of a vast collection of stars called our galaxy. At the end of the lecture, a little old lady at the back of the room got up and said, "What you have told us is rubbish. The world is really a flat plate supported on the back of a giant tortoise."
The scientist gave a superior smile before replying, "What is the tortoise standing on?"
"You're very clever, young man, very clever," said the old lady. "But its turtles all the way down!"

—Stephen Hawking, A Brief History of Time, 1988

The notion of the world residing atop a turtle's back is a common one in creation mythology. In Cheyenne legend, before humans existed, the world was covered in water. The Creator, Maheo, placed the first land (and all subsequent land, I assume) on Grandmother Turtle's back. You can guess where earthquakes come from… But while the original turtle in this story is obviously a sea turtle, it is believed that turtles first appeared on land.

Two-hundred million years ago, the first reptiles set out to explore the land, uninhibited by their amphibian ancestors' habit of drying out. These reptiles were the tree trunk for all vertebrate evolutionary experiments above the amphibian level. One branch developed into a most improbable creature that, since its inception in the fossil record, has rarely changed its body plan through the course of (a very long) time.

Not much is known about how the turtles first acquired their shells, though at least one intermediate form has been discovered: Odontochelys semitestacea appeared in the Triassic period, circa 220 million years ago, and has a complete plastron (belly shell) but only a partial carapace (back shell). A turtle's shell is actually the animal's backbone and ribs that have flattened and fused together and are covered by scaly plates. The earliest complete turtle is also found in the Triassic, about ten million years after O. semitestacea. Proganochelys quenstedti very much resembled modern turtles, if modern turtles had to contend with dinosaurs. Like today's sea turtles, P. quenstedti couldn't retract into its shell to hide from predators. Instead, he came fully equipped with a spiked neck and a spiked tail ending in a club. These eventually went out of style, but the basic dress was set, and the early turtles had settled on a design that allowed the fullest expression of meditation and passive resistance, a new philosophy for reptiles. Through the rise, spread, and eventual fall of dramatic new body plans (pteranodons, mososaurs, brachiosaurs…) they remained conservatively turtles, though some took to the sea, sacrificing parts of their time-tested shell for greater buoyancy, but always clinging to the same structural plan.

There are seven species of sea turtles alive today. All species except the leatherback sea turtle are in the family Cheloniidae. The leatherback is the sole member of family Dermochelyidae. Species are primarily distinguished by anatomy. Leatherbacks are the only species without a hard shell, hence their relegation to a different family.

Since sea turtles live most of their lives submerged, they have developed an anaerobic system of energy metabolism (anaerobic = no oxygen). All sea turtles need to breathe air, but under dire circumstances, or if the water grows very cold, they can adjust their metabolic rate and remain underwater for hours. When they are active, they typically need to breathe every few minutes. If needed, they can also go two to three months without food (perks of being a reptile).

As you might guess, they drink exclusively sea water, but just like us, excessive salt intake can be a health risk. Sea turtles have evolved special glands to excrete the excess salt; they cry salty tears. Despite frequent crying, these animals have fairly good eyesight under water, though they are shortsighted in air. They also have a good sense of smell and are sensitive to touch on the soft part of their flippers and shells. Sea turtles don't have an ear opening, but like other reptiles, they have a single bone in the middle of the ear that conducts vibrations to the inner ear. They hear low frequency sounds and vibrations. Taste? Well, there's no accounting for that.

A sea turtle's day typically consists of eating and sleeping, and possibly migrating. They may sleep floating at the surface or wedged under some rocks or coral. Hatchlings typically sleep while floating with their front flippers folded back over the tops of their backs. For the most part, they are solitary creatures, though some do congregate in large numbers during nesting, feeding, and migration. But even then, there is almost no social interaction.

Sea turtles return to land only to lay eggs (so most males never return). How the females find the beach they hatched on in order to lay their own eggs is not fully known. Some scientists hypothesize that baby sea turtles imprint on the particular smell, chemical make-up, or magnetic location of the beach where they hatched. They do have an iron ore, called magnetite, in their brains that makes them sensitive to the Earth's magnetic fields. Why they don't nest on beaches identical to, or even better than, the ones they hatch on is unknown. It may be that they use the same beaches that were ideal for nesting centuries ago and have not adapted to the new conditions on some beaches.

Temperature determines the sex of the hatchlings. Cooler temperatures favor the development of males; warmer temperatures usually produce females (hello global warming). Even minor differences in temperature can have an effect. Example: the center of the nest is warmer, so those eggs will likely hatch into females, while the cooler eggs on the outside are more likely to be males. Hatchlings must dig themselves out of the nest and execute a mad dash to the ocean. Many are snatched up by shorebirds before they reach the water, and many more are eaten by watery predators just when they get their flippers wet. The obstacles are so disproportionately against hatchlings that only one in a thousand will survive to sexual maturity.

There are five species that can be found on the Texas coast: Kemp's ridley, hawksbill, loggerhead, leatherback, and green. All except the loggerhead are endangered (and even it is threatened).

Kemp's Ridley Sea Turtle
Known as tortuga lora (parrot turtle) in Mexico, this is the smallest, and most endangered, of all sea turtles. It can grow up to 32 inches long, 100 pounds, and live up to 50 years (reaching sexual maturity in 10-15 years). The carapace is dark gray to gray/green, the plastron is cream to tan, and the head and flippers are dark and spotted. They are carnivores, preying mostly on crabs, but will also take shrimp, snails, clams, jellyfish, sea stars, fish, etc. Kemp's ridleys are one species that nests in large congregations, called arribazones, and one of the few that lay their eggs during the day. The nesting beach at Rancho Nuevo, Tamaulipas, Mexico, is the primary, and only known major, nesting site for this species. A secondary nesting population was successfully established on Padre Island National Seashore in 1992, after 14 years of work. A female can lay up to 100 eggs in a season. If you happen to see some nesting, let your local park ranger or game warden know! And let them be; egg laying is kind of private… Other than nesting, you can sometimes see these turtles hanging out in the bays.

Hawksbill Sea Turtle
Hawksbills are the most tropical species of sea turtle. Though they are occasionally found in coastal waters, they stay offshore more often than not. They can reach 36 inches in length and live up to 50 years, reaching sexual maturity at three to five years (in captivity; may take longer in the wild). They are carnivorous, feasting mostly on invertebrates, including sponges, jellyfish, crustaceans, sea urchins, mollusks, etc. Females nest at night in the spring, laying about 200 eggs per nest, and several nests per season. The hawksbill's brown shell with brightly colored spots and streaks is the source of "tortoise" shell jewelry. Tortoise shell artifacts have been recovered from several ancient cultures, and harvest of this turtle for its shell is still a threat to its survival in some areas of the world.

Loggerhead Sea Turtle
Found worldwide, loggerheads can live in coastal lagoons, river mouths, really any non-freshwater above 50 degrees Fahrenheit. Though they often stay offshore, they do winter in shallow waters. They have characteristically large heads with powerful jaws, can reach 45 inches long, weigh 500 pounds, and live up to 50 years. Though feeding behavior may change with age, they are carnivorous, and at some point in their lives will consume conchs, clams, crabs, horseshoe crabs, shrimp, sea urchins, sponges, fish, squids, octopuses, jellyfish, floating mollusks, egg clusters, and flying fish. Loggerheads are the only sea turtles that nest successfully outside the tropics, and also the only ones who don't mate by their nesting beaches. It's assumed they mate along migration routes between feeding and breeding grounds. They nest during spring and summer nights. Each female lays about 190 eggs per nest, several nests per season. Hatchlings of this species are frequently found in sea fronts, downwellings, and eddies, where floating open ocean animals seem to end up. The time spent in these areas, feeding and growing, is called the 'lost year' because tracking them during this time is difficult, and their whereabouts are often a mystery. They spend this "year," which can actually last several years, floating on rafts of seaweed, feeding on other creatures associated sargassum mats. While the meat and leather of this species aren't as valuable as the green sea turtle, and the shell is not as highly prized as the hawksbill's, overharvesting and incidental catch are still taking their toll. Loggerheads and Kemp's ridleys are especially likely to be caught in large shrimp trawl nets because of their shallow water habits. However, today's shrimp boats are required to have turtle excluder devices, which help reduce mortality from net entanglement.

Leatherback Sea Turtle
Leatherbacks are the largest, and fastest growing, of all sea turtles, growing up to eight feet long and 1300 pounds. They are one of the largest living reptiles, surpassed only by some species of crocodiles. Sexual maturity is reached in three to four years (in captivity), and they can live at least 50 years, possibly longer. They have a smooth, unscaled, leathery skin covering the carapace, which shifts them into a different family than all the other sea turtles. The menu is a little more varied in this species. They mostly eat pelagic invertebrates, especially jellyfish and tunicates, but they are omnivores and will also feed on fish, crustaceans, algae, floating seaweed, etc. Though they are found in the Gulf, they rarely visit coastal waters. Nesting occurs in the fall and winter in arribazones during the night. A female lays about 100 eggs per nest and can have several nests in a season. Leatherbacks are listed in the Convention on International Trade in Endangered Species as one of the most highly endangered animals worldwide and are protected in most countries. In the past, leatherbacks were killed for the abundant oil they yielded, which was used for oil lamps and caulking wooden boats. Though poaching does exist, the most serious threat to the species is disturbance of nesting grounds, i.e. egg harvesting. Captive breeding has been attempted, but so far, has been largely unsuccessful.

Green Sea Turtle
Green sea turtles are the largest of all the hard-shelled sea turtles, but have a comparatively small head. They grow up to 55 inches and 850 pounds, and live up to 50 years, reaching sexual maturity between eight and thirteen. They are named, not for the color of the shell (which is normally brown or olive), but for the greenish color of their skin. Adults are strictly herbivorous, feeding on seagrasses and algae. Unlike most sea turtles, who sun themselves by swimming close to the surface in shallow waters, greens will actually bask on land. They are one of the few marine turtles known to leave the water for reasons other than nesting. Nesting occurs in the summer; females can lay up to 145 eggs per nest, and several nests per season. Greens have long been harvested as a food source. Though international trade is illegal, local consumption still exists in many areas of the world.

Ecological Impact
Sea turtles eat jellyfish, even the stinging kind, helping to prevent large blooms that wreak havoc on fisheries, recreation, and other maritime activities. They are also an important attraction for coastal tourism, but probably the most important role they have is as a keystone species: a species whose presence and role within an ecosystem has a disproportionate effect on the environment relative to abundance. A keystone species is often a dominant predator whose removal allows a prey population to explode, resulting in a decrease of overall diversity. Research has shown that sea grass beds grazed on by green sea turtles are more productive than those that aren't. Hawksbills specialize in eating sponges, preventing the sponges from out-competing the slower-growing corals. Both of these grazers do their part in maintaining the natural balance of those ecosystems. If they were suddenly removed from those systems, the balance would be changed, possibly with negative effects for the species that depend on the status quo of seagrass beds and coral reefs, which could include species that we harvest. Danger, Will Robinson!

…and we're off! Like a herd of turtles...

Where I learned about sea turtles, and you can too!

TPWD (assorted turtles)
Kemp's ridley:

NOAA Fisheries

The Turtle Nest

Science 2.0

Sea Turtle Conservancy

Sea Turtle Conservation Bonaire

Archie Carr Center for Sea Turtle Research

Mythical Creatures Bible: The Definitive Guide to Legendary Beings, by Brenda Rosen

Four great rivers to cross: Cheyenne history, culture, and traditions, by Patrick M. Mendoza, Nico Strange Owl

A Cheyenne Myth, retold by Alice Marriott & Carol K. Rachlin

Sea turtle identification:,
Sea turtle: resuscitation guidelines: NOAA Southeast Fisheries Science Center,