I’m kneeling on a sandy beach in Costa Rica on a balmy January night helping biologists administer an ultrasound to a leatherback sea turtle. They are hoping to learn more about her reproductive cycle, to better protect populations of this endangered reptile at its nesting beaches around the world. The turtle has come ashore to lay her eggs, as her kind have done since dinosaurs roamed the earth. I watched as she hauled her enormous bulk up the beach, pivoted slowly around to face the ocean, and began scooping out an oval pit in the sand with her hind flippers. She soon entered her egg-laying trance, a quiescent state in which she remains for an hour until she covers over her nest and heads back to the surf.
In her reverie, she takes no notice of us as we get to work. We unpack the equipment, which looks like a desktop computer, and set it down in the sand just behind her. A switch is thrown, and flickering light from the screen lights up the turtle’s hind end. Two of us, one on each side, hold down her huge front flippers to ensure that she doesn’t start flinging sand in our faces when she begins concealing her nest. Those oarlike flippers can toss any one of us aside like so much flotsam, but they lie idle at her sides. I feel for her in her labor. Her weight makes it difficult for her to breath, and she sucks in air in great gasps. Tears designed to carry away excess salt dribble like saliva from her eyes, making her look as if she is crying from the strain.
We wait while she drops about 100 moist, white eggs into the nest. When she is finished, David Rostal, a biologist at Georgia Southern University, carefully moves the ultrasound probe across her skin over her uterus. Though I am familiar with ultrasounds, having watched the development of my own two babies, I cannot decipher the picture that forms on the screen. To Rostal, however, it reveals whether she has mature ovaries bearing preovulatory vitellogenic follicles-that is, whether she will return later in the season to lay another batch of eggs.
Notwithstanding my familiarity with ultrasounds, I find it truly incongruous to witness one of the most modern of medical tests being used on one of the most ancient of animals. Yet such scenes are becoming increasingly common. Today, on lonely mountaintops, in remote stretches of rainforest, and far out in the oceans, scientists are turning to all manner of high-tech tools to help them study threatened wildlife. Techniques range from tracing family trees of endangered species by analyzing their DNA to using video cameras strapped to sperm whales to film giant squid in their natural environment. In many cases, these advanced technologies are allowing scientists to investigate aspects of ecology, physiology, and behavior that they were never able to investigate before. And by enabling researchers and wildlife managers to identify crucial missing links in animal life cycles, the techniques are bettering endangered species’ chances for survival.
The work taking place with leatherbacks on this beach-Playa Grande on Costa Rica’s Pacific coast-is a case in point. For on that half-mile-long stretch of sand, biologists are making use of perhaps more high-tech gadgets than any other biologists working on any other animal. And with these tools they are answering a sea of previously unanswerable questions about the turtles-and so learning how remarkable they are and what kinds of conservation measures may help them.
The Leathery Turtle
Dermochelys coriacea, “the turtle covered in leathery skin,” is unique among sea turtles, which also include the loggerheads, greens, hawksbills, and ridleys. It is the most ancient living reptile, around in its current form for at least 20 million years and possibly over 100 million years. It is also the biggest, having watched its rivals for size, the dinosaurs, go extinct some 65 million years ago. The female before me this tranquil night checks in at about five feet long and 550 pounds, the average for nesters on Playa Grande. But a male leatherback once caught in fishing nets off the coast of Wales stretched fully nine feet from head to tail and weighed a ton.
Despite their bulk, leatherbacks migrate farther and dive deeper than any other reptile-indeed, than almost any other animal. After nesting in the tropics, the giant turtles typically swim thousands of miles to reach their favorite feeding grounds in subpolar waters. Along the way, they regularly dive more than 3,000 feet straight down, in search of food or to escape the rare predator such as a killer whale. Their streamlined black body, with its smooth, leathery skin and ridged, highly tapered carapace-which lends the species the popular names of “keelback” and “trunkback”-eases long-distance swimming. A collapsible body frame that includes a high cartilage-to-bone ratio and few fused ribs (even their shell is as flexible as an eraser) allows leatherbacks to deal with the pressure, which at 3,000 feet approaches 1,500 pounds per square inch. Astonishingly, they manage all these feats on a diet of nothing more than jellyfish.
Despite its uniqueness, the leatherback is on the road to extinction. Frank Paladino, a biologist at Indiana-Purdue University at Fort Wayne who has run the project at Playa Grande since 1988 with James Spotila of Drexel University, recently estimated that the global population has dropped by two-thirds since 1980 alone, from 115,000 to 34,500 nesting females. (Censusing males is impossible, as they never come ashore and are rarely observed in the open ocean.)
Though the leatherback spends most of its life far out to sea, its chief threats, ironically, lie ashore. Laying its eggs on land is the one trait it has retained from its earliest ancestors, the land-dwelling tortoises, and that trait has now come back to haunt it. On leatherback nesting beaches throughout the tropical world, people raid the turtle’s nests for their delectable eggs, build over their habitat with houses and hotels, and occasionally kill nesting females for their meat. Increasingly, though, leatherbacks are also losing their lives on the high seas, where fishermen harpoon them for food or for the thick, yellow oil contained in their flesh. (The oil is used in the Caribbean as an aphrodisiac or as a chest rub to relieve congestion and by fishermen in Arabia and India as a treatment for boat timbers.) The turtles also perish at sea when longline fishing gear unintentionally snags and drowns them, and floating plastic garbage chokes them when they mistake it for jellyfish.
To slow or even reverse this precipitous decline, biologists are rushing to better understand the species. “We desperately need to know where these animals go in the open ocean and what they do out there,” says Scott Eckert of the Hubbs-Sea World Research Institute in San Diego, Calif.
Biologists have no idea where the turtles, which depart their natal beaches as two-ounce hatchlings, spend their developmental years. Nor do they know how fast they grow, at what age they reach sexual maturity, or how long they live. They’re not sure how females find their way to feeding grounds, or how they find their way back to their favorite nesting beaches. No one has ever reported seeing leather-backs mate. “When you realize those very basic pieces of information are missing, you realize why we’re having such a struggle trying to save these creatures,” says Eckert, who says he has begun to fear, for the first time in 15 years in the field, that their extinction may occur in his lifetime.
Turning to Technology
When we finish with the ultrasound, we all step back and watch the turtle cover over her nest. Her giant front flippers send shovelfuls of sand flying behind her, and within minutes I can only guess where the nest actually lies. Leatherbacks must take special care to conceal their eggs, as many non-human predators-from mongooses to dogs-also dig them up. Soon she finishes her work and begins dragging herself down the berm toward the breaking waves.
But we are not through with her yet. Rostal wants to take a blood sample, to see if there is a correlation between her testosterone levels and the presence of those preovulatory follicles. The goal is to discover what triggers a female to lay her eggs and, when she’s done, to leave the region for the season. By better understanding the egg-laying cycle, conservationists can know not only where but more precisely when to extend protection to nesting females.
No longer in her trance, the leatherback is now hellbent on reaching the water and will not sit still while we try to draw her blood. So we lay down a tarp of thick rubber webbing in her path. When she crawls onto it, we take up the four corners and, after several attempts, succeed in pinning her powerful flippers at her side. Rostal wastes no time in getting the sample, which he extracts from her neck with a long hypodermic needle. Along with samples from other turtles, the blood later reveals that females bearing mature ovaries with multiple large follicles, such as our turtle that night, do show high testosterone levels, while those with depleted ovaries have correspondingly low levels of the hormone. Such clues to the timing and mechanics of reproduction will help scientists better monitor discrete leatherback populations across the tropics, from Mexico to Malaysia.
As sophisticated as the blood and ultrasound testing are, they represent just the tip of the proverbial iceberg for Paladino and other leatherback researchers. In their efforts to gather as much information as they can about each turtle, nest, egg, and hatchling on Playa Grande and elsewhere, they rely on a wide range of techniques. Certain methods remain low-tech, such as recording each mother’s carapace length and width with a measuring tape (to determine average sizes of nesters there) and marking the exact location of each nest with a wooden stake (to learn what makes an ideal nesting site). But other methods rely on some of the most advanced technologies available.
Arguably the most valuable technology Paladino employs at Playa Grande is also the smallest. About the size of a grain of rice, the Passive Integrated Transponder, or PIT, is a glass-encapsulated microchip identification tag that his team injects into the shoulder muscle of every nester that crawls onto Playa Grande. PIT tags are more reliable than metal flipper tags, which Paladino uses as well, even though they often fall off during the animal’s peregrinations at sea. As each turtle comes ashore, project staff members pass a hand-held scanner, like those used in supermarket checkout lines, across the reptile’s shoulder to read the I.D. code.
By identifying individuals, researchers can answer a bevy of questions. Over the years, Paladino and his colleagues have proven, for instance, that Playa Grande-which at its height in the late 1980s saw about 1,600 nesters a season-is one of the largest leatherback nesting colonies in the Pacific Ocean. They have also shown that females tend to lay eggs, on average, five times during the October-to-February nesting season. This finding may have conservation implications. For example, if females hang around relatively close to the beach, boating and fishing near nesting beaches may need to be restricted during these months.
Paladino now hopes to begin implanting PIT tags into newborns. Though he fears that as hatchlings grow, the tags may become so buried in dense tissue that they become unreadable, he hopes enough will remain viable sufficiently long to help clear up such enigmas as how fast leatherbacks mature. For instance, if a tagged newborn female returns as an adult to its natal beach to lay eggs-as many researchers believe leatherbacks do-then, with a quick read of the tag, the scientists can know just how old that turtle is and how long it took to reach sexual maturity.
Other technologies that come into play on shore shed light on leatherback physiology. As each turtle on Playa Grande lays her eggs, Paladino’s crews place the wires of a thermocouple, which measures temperature, into the nest during the 60-day incubation period. Nest temperatures, it turns out, largely determine the sex of hatchlings. Warmer temperatures mean more females, colder temperatures more males. The temperature at which an equal proportion of the two sexes results reportedly lies between 84 and 86 degrees F. Therefore, knowing the nest temperature on Playa Grande and other beaches (which may vary slightly) is crucial to conservation efforts, which often include relocating nests that are prone to egg-poaching or seawater erosion.
One of the most tantalizing mysteries surrounding the leatherback is how it manages to survive in icy waters. Leatherbacks have been caught in 44 degrees F waters with internal body temperatures of over 77 degrees F. Some biologists have suggested they must have high metabolisms, like mammals or birds. But biologists Frank Paladino and James Spotila believe otherwise.
To analyze the turtle’s resting metabolism, the two researchers placed sealed masks over the heads of nesting leatherbacks and collected their respiratory gases in large meteorological balloons. They later analyzed the gases for total volume and percentages of oxygen and carbon dioxide to develop an estimate of the turtle’s resting metabolic rate-the amount of oxygen it burns per kilogram of body weight-after sitting immobile on shore for two hours. They found that leatherbacks have a metabolism less than half that of a similar-sized mammal, such as a cow.
Paladino and Spotila theorize that leatherbacks are relying on a unique metabolic system they have termed gigantothermy. Gigantotherms-which may have included the dinosaurs, they say-have large body sizes and low metabolisms, and they use peripheral tissues (in the case of leatherbacks, their blubbery skin) as insulation. In leatherbacks, for instance, arteries and veins lie side by side, so that heated blood pumped out from the heart can warm chilled blood coming in from the extremities. This helps to keep the turtle’s core body temperature high even in waters that would kill a human in minutes.
Trailing the Trunkback
The most exciting insights biologists have gained into the lives of leatherbacks have come from data-gathering devices that unsuspecting females have carried with them into the deep sea. “We’ve always been accused of studying animals in a maternity ward,” laughs Eckert, referring to working with females on and near nesting beaches. “Now we can step back and find out what they spend the other 99.9 percent of their lives doing.”
Some of the earliest clues into leatherback behavior at sea, for instance, came from microprocessor-controlled time-depth recorders (TDRs). Attached to the animals’ shells, these instruments, which biologists initially designed for studies of other great divers such as seals and penguins, record dive depth and duration, ascent and descent rates, and surface times. Eckert and his wife Karen, who is also a leading leatherback researcher, first shed light on the turtle’s diving skills using TDRs on nesters departing Sandy Point, St. Croix. The females, they found, dove almost continuously, day and night, averaging ten minutes a dive and five dives an hour. They also dove more deeply during the day, often to profound depths. One turtle swam down 3,330 feet before the TDR stopped recording. While that dive remains the deepest on record, Eckert thinks leatherbacks routinely dive far deeper. After analyzing hundreds of dives, the husband-and-wife team believes the turtles are following the so-called deep scattering layer, a horizontal zone rich in jellyfish that rise to the surface at night to feed on phytoplankton but retreat during the light of day to depths below 1,800 feet, where the illumination is but 1 percent of that at the surface.
Biotelemetry, a means to remotely detect and measure movements and other conditions of wildlife fitted with electronic telemetry devices, has also helped clarify leatherback behavior on the high seas. To learn more about what Playa Grande females do in the days or weeks between nesting events, Paladino and his colleagues fitted individuals with radio and sonic transmitters and trailed them in boats as they left the beach. The radio transmitters allowed the scientists to monitor the surface activity and location of turtles up to 10 miles away. The sonic transmitters, whose sound waves travel readily through water, enabled them to record dives to depths of 1,500 feet and more.
Through this work, Paladino and his colleagues discovered, among other findings, that females awaiting another chance to nest spend their time diving and feeding at relatively shallow depths within about 40 miles of Playa Grande. At the end of a day of study, the researchers simply dove into the water to retrieve their instruments when the turtles surfaced.
For turtles heading off on their long-distance migrations, the biologists needed equipment that could operate remotely. Satellite telemetry was the answer because tracking turtles this way, Eckert points out, means that “you don’t need to chase them around.” In June 1995, he outfitted three leatherbacks on a beach in Trinidad with one-watt satellite transmitters, each bearing an onboard microprocessor that recorded dive depths and durations. Each time a turtle surfaced, the transmitter looked for one or both of the Argos polar-orbiting weather satellites, each of which passes over the equator about four times a day. When a link was made, the transmitter sent a code identifying the turtle as well as a stream of data. The satellite, in turn, used a triangulation function to determine where on the planet the signal was coming from. If the turtle remained on the surface long enough, then the satellite got a solid fix on its location, often to within 500 feet, Eckert says. The satellite relayed the information to a ground-based receiving station, which forwarded the data by email once a day to Eckert’s office computer.
For the first time, scientists were able to get a detailed look at where leatherbacks go on their ocean-spanning migrations. One of Eckert’s transmitters failed after three months, but the other two each lasted for more than a year. (Eckert designed them to give out after about 40,000 transmissions, and for the harness that carried them to fall off the turtle after about a year.) In that time, the two turtles traveled more than 10,000 miles each. After leaving Trinidad, one headed north into subarctic waters, where it lingered for two months before heading south to the Canary Islands and onto to Africa. The other swam east, veering north about 1,000 miles west of Mauritania. It wound up in the Bay of Biscay off France, then turned south, eventually approaching close to the African coast.
In the meantime, Eckert has been trying to improve his telemetric techniques. He recently outfitted nine leather-backs on the Pacific coast of Mexico with improved transmitters designed to last for 250,000 transmissions over as long as 4 years. And he is now working on a transmitter that will use the Global Positioning System (GPS) to follow his turtles. “The beauty of a GPS location is that it’s very easy to get,” he says. Typically leatherbacks stay on the surface for only a few minutes, but the transmitters on his Trinidad subjects needed the turtles to be on the surface for at least five minutes to obtain a satellite fix. The GPS unit needs less than 20 seconds. Further, during that time Eckert will be able to communicate with the transmitter. “You can reprogram it, such as tell it to turn itself off for a month if you’re getting data from areas you don’t want,” he says.
While satellite-tracking eight leatherbacks on the Pacific side, Paladino and his colleagues made an interesting discovery. Turtles leaving Playa Grande can depart anywhere along an arc of about 160 degrees. Yet all eight turtles in the study headed southwest along the subterranean Cocos Ridge to the Galapagos Islands; four continued past the Galapagos into deeper Pacific waters. The biologists believe the turtles are migrating along distinct ocean corridors, which they conservatively estimate to be about 300 miles wide. At Playa Grande, Paladino has begun to investigate how the turtles sense such routes. Normally newborn leatherbacks exiting the beach invariably head straight out to sea. But when Paladino temporarily glued magnetized needles with about twice the strength of the planet’s magnetic field to the turtles’ heads, they began wandering aimlessly. “When you disrupt their ability to sense the earth’s magnetic field,” he says, “they seem to go in a random pattern.”
Eckert considers the jury still out on whether specific pathways exist; his three Trinidad turtles, for instance, headed in three different directions. If such corridors do exist, however, they could go a long way to help protect the species on the high seas, Paladino says, for authorities can know when and where to restrict the long-line fishing operations that drown thousands of leatherbacks each year. Indeed, the new knowledge about leatherback behavior that biologists are now collecting is giving them renewed hope that the species can be pulled back from the brink of extinction. “Using satellite telemetry and other technologies that allow us to understand leatherback movements and habitats,” says Eckert, “gives us the tools we need to respond, for instance, to fishermen who say We want to build a new fishery out here.’ We can say, Fine, but here’s what you need to avoid.’”
Preserving the Species
After taking the blood sample, we release the leatherback from her temporary bondage and watch as she hauls herself toward the breaking surf. The high tide, which she had relied on to carry her as far up the beach as possible, has begun to go out, making her journey more taxing than on the way in. She breathes hard, and the bulbous flesh on her neck and shoulders glows crimson from the exertion. But she presses on, leaving a track in the sand five feet wide. Before long, the first frothy waves begin splashing over her broad back. A few minutes later, she regains buoyancy and instantly vanishes into the sea.
More research will be needed to determine whether this leatherback then swam down a sea-turtle highway to her feeding grounds-and to solve an ocean of other mysteries about leatherbacks. Some questions, such as where baby turtles go when they disappear into the waves, may have to await breakthroughs in available technologies, such as miniaturized satellite transmitters perhaps, or even new technologies altogether. “When I think about trying to figure out where those hatchlings are going out there, it makes me blanch,” Eckert says. But it hardly deters him. “We have to get a better understanding of where leatherbacks go, what they’re doing out there, and what habitats they need to survive, or we’re wasting all our efforts everywhere else,” he adds, referring to attempts to safeguard nesting beaches. “That’s my crusade of perhaps the next 50 years.”
Another crusade of Eckert’s is informing the general public about leatherbacks and their plight. “It’s your long-term insurance,” he notes. One of the best ways to educate people, he says, is with yet another burgeoning technology-the Internet. There are now a number of popular sea-turtle-oriented Web pages, and some researchers, including Paladino’s colleague Edward Standora of Buffalo State College in Buffalo, N.Y., have begun to put their satellite tracks out over the net, so schoolchildren can watch the turtles’ progress. “The Internet is an inexpensive way to distribute information to a very wide readership,” Eckert says, “and any time you do that you’re benefiting conservation of the species.”
Meanwhile, until wider scientific understanding of leatherbacks exists, researchers agree that the most promising way of preserving the species remains protecting its nesting grounds. Toward that end, there is good news at Playa Grande. In July 1995, the Costa Rican government declared Playa Grande and two neighboring nesting beaches a national park, Parque Marino Las Baulas, or “Leatherback Turtle Marine Park.” Beyond a strong national conservation ethic, the Costa Rican authorities granted protection largely based on Paladino’s and Spotila’s cutting-edge research.
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