The plight of the turtle. (Life science: conservation/ecology)(Cover Story).

VITAL STATS: Leatherback (Dermochelys coriacea)

Average weight: 499 kilograms (1,100 pounds)

Average length: 1.8 meters (6 feet)

Life span: About 50 years

Diet: Mainly jellyfish 

Habitat: Leatherbacks are highly migratory and swim the world's oceans. They've been spotted as far north as Nova Scotia, Canada, and as far south as Chile.

Main nesting beaches: Mexico, South America, the Caribbean

Status: Endangered

Population: An estimated 30,000--down from 115,000 in 1980

Threats: Egg harvesting, disturbance of nesting grounds, drowning in fishing nets, choking on plastic bags mistaken for jellyfish

It's as ancient as the dinosaurs and the most giant reptile on Earth. But the leatherback turtle also ranks as the most endangered of all seven sea turtle species that exist today. Some scientists predict that without urgent conservation, this living prehistoric relic may go extinct in a decade. What's so amazing about the leatherback turtle and why is it worth saving? Marine biologist Scott Eckert of Wider Caribbean Sea Turtle Conservation Network talked to Science World.

Q: Why is the leatherback the most endangered sea turtle?

A: We divide leatherbacks into three or four large groups based on where they nest or live. While every population is a little different, the Pacific population dropped well in excess of 90 percent in the last 15 years. Now, fewer than 5,000 females nest in the region.

Q: Why this big die-off?

A: The common theme has been egg harvesting and the killing of adults on beaches, combined with fishing activities. For example, swordfish gill-netting was introduced off South America in the early 1980s: The fishing industry learned to use smaller vessels that go into the high seas, stringing 100-mile-long nets. While the nets catch a lot of swordfish, they also kill any marine life that swims into them. Fishermen in Chile and Peru were catching 3,000 leatherbacks per year. Before gill-netting, some 80,000 leatherbacks nested in Mexico and Costa Rica each year. Now they're down to about 600.

Q: Why are turtle eggs so valuable?

A: Turtle eggs have traditionally provided a protein source for people all over the tropical world. Leatherbacks produce anywhere from 65 to 80 eggs per clutch (nest) and lay about 11 clutches per season. A beach with 1,000 nesting females is a huge opportunity to harvest food. This reached epidemic proportions in the 1970s and '80s, when truckloads of eggs were sold on international markets.

Q: That's a huge problem!

A: These turtles have a life span that exceeds 50 years, and only 2 to 3 percent of adults die naturally each year. They don't become reproductively mature till they're about 20. By taking away the eggs, the leatherback is still going to be around for a while. But when all the adults die, the population will go extinct.

Q: The leatherback spends 99 percent of its life swimming. What propels it?

A: You don't find any other sea turtle designed quite as nicely for hydrodynamic efficiency (ease in moving through water). The leatherback has the classic Olympic swimmer's shape--big broad shoulders, long front limbs with giant paddles, and huge pectoral muscles. And those ridges down its back help the leatherback travel straight so it doesn't need to do a lot of sculling (rowing arms like oars) sideways. On top of that, the ridges have little bumps, which break surface tension (clinging force on the surface of a liquid): If the body is too smooth, water tends to suck at it, making it harder to swim. The bumps break this tension, allowing the turtle to glide through water more efficiently.

Q: What fuels this marathon swimming?

A: A large diet of jellyfish, which is almost pure protein. Somehow the leatherback can convert that protein into fat and oil very quickly. Even if the jellies aren't out, the turtle will have enough fat reserve for the energy to swim to the next foraging area. Also, leatherbacks have characteristics that other sea turtles lack.

Q: Like what?

A: Think about how far it is to swim 10,000 km (6,214 mi) a year or 45 to 60 km (28 to 37 mi) per day. These are just horizontal distances.. Their vertical distances are equally mind-boggling: This turtle can dive up to 4,000 ft (1,219 m). That's partly because the leatherback can keep warm: Besides heavy fat insulation, it also has the perfect shape for heat retention. In a cross-section of the turtle you'll see an almost perfect cylinder, which means maximum mass for minimal surface area. Also, constant swimming generates heat. These turtles have been spotted swimming by icebergs. No other sea turtle is as fearless of expanse.

Q: Unlike other sea turtles, the leatherback's carapace (shell) is leathery and flexible. Does that make it more vulnerable to predators?

A: They're certainly vulnerable to killer whales, which occasionally feed on them. But killer whales can't dive as deeply. The hard shell is great for turtles like the green or hawksbill, which live near reef areas. They can use the shell to hunker down and hide beneath a rock or use it as a shield against predators. But leatherbacks can't hide in the open ocean. And to be armored enough to protect it from a shark or whale would entail a shell too heavy to swim in.

Q: Why don't leatherbacks get out of the water?

A: If there's anything maladaptive (not fit for survival) about this turtle, it would be that females must crawl up a beach to deposit eggs. Males never come on shore--and if you've seen a female on the beach, you'd know why. Here's an extremely heavy animal with a body that's not structurally very strong--it's designed to go with the flow. She has to haul 800 pounds of dead weight with her flippers and chest up a very steep beach. Most nesting beaches tend to be near high surf. Then she spends an hour digging a nest with what looks like two baseball gloves for rear flippers. It's tremendously stressful.

Q: Is nesting time the only opportunity to study them?

A: We needed a better understanding of where the turtles were going. So I developed a technique where I put dive recorders and satellite transmitters on nesting females. This allows us to track them over long distances.

Q: Where do they go?

A: We've seen leatherbacks swimming between France and Trinidad. Some literally circumnavigate the Atlantic Ocean. While most of the time we've tracked leatherbacks across oceans, leatherbacks leaving Florida behave somewhat differently. These leatherbacks often remain in coastal waters from North Carolina to Virginia after they finish nesting in Florida.

Q: Do you know why?

A: Right now I'm convinced there are two factors that motivate the leatherback: breeding and feeding. We're beginning to discover that they're patch feeders. They feed on one high-density food patch after another. For Florida turtles we've noticed there are plenty of jellyfish near shore. And if there's plenty to eat close by, why swim 10,000 kilometers?

Q: What's to learn next?

A: I'm still learning a lot about the leatherback's food source. We're also developing techniques to take a fat sample from a leatherback and determine what kind of jellyfish it ate. This will help us understand what ecologists call niche identity--how and why the leatherback fits into the marine ecosystem. We also need to know why fish and turtles wind up at the same place, and if we can separate the two so, fishermen can fish without catching turtles.

Q: Some people may say: It's just a turtle. So what?

A: My grandmother used to say, "I didn't miss the dinosaur, why should I miss the leatherback?" The answer is, we're just beginning to understand the unique role the leatherback plays in the ecosystem. Think of the food web: The leatherback eats jellyfish. And jellyfish eat fish larvae, plankton, or small fish--either fry (young) of big fish or food for bigger fish. Now some commercial fish species like cod and pollack have been depressed due to overfishing. Because jellyfish are so abundant, their competitive feeding habits are preventing cod and pollack from recovering. At the same time, fishermen are catching leatherbacks. The irony is leatherbacks eat jellies as fast as they can stuff them in. We need the leatherbacks to keep the marine ecosystem healthy.

Q: Is there a solution to save this species?

A: There's competition between humans and turtles for resources. We must figure out what are the turtle's needs, what are human needs, and work with the fishing industries to fix the problem. If all this comes together, we'll be able to find a solution. But we're in a hurry, because we don't have a lot of turtles left.

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Did You Know?

* The leatherback turtle is around 90 million years old. It's one of the oldest living vertebrates on land or sea. The oldest marine mammal is estimated to be only about 25 million years old.

* A Galapagos tortoise shows dominance in the social hierarchy by the height to which it can stretch its head and neck.

* The Galapagos was named after the giant tortoises. The word is Spanish for "saddle" and was used to describe the tortoises' huge shells. Today, the giant tortoises are actually classified into three distinct physical types. Saddle-backed have raised shells, long necks and limbs. Dome-shaped have round shells and very short necks and limbs. Intermediate is a mix of both.

Cross-Curricular Connection

Language Arts: Research the life and threats of Galapagos tortoises. Then challenge students to write a personal ad for Lonesome George.

Critical Thinking:

Have students review the food web. Then come up with a possible chain of disastrous events that may occur if either the Galapagos tortoises or the leatherback turtle go extinct.

CHECK FOR UNDERSTANDING

Name--

Directions: Answer the following questions in complete sentences.

1. What are the three main factors endangering the leatherback turtle?

2. Why is the leatherback well adapted for life in the open water? Include at least three defining features.

3. Most leatherbacks swim the open ocean. What did marine biologist Scott Eckert conclude by studying the Florida population that hovers along coastal waters?

4. Why are leatherbacks important for the marine ecosystem?

5. What caused the Galapagos tortoise populations to plummet?

6. Why is Lonesome George unlike the other Galapagos tortoise subspecies, and why is it critical to save him?

ANSWERS

1. The three main reasons the leatherback turtle is endangered are as follows: egg harvesting, killing of some adults on the beaches, and fishing activities.

2. The turtle is designed for hydrodynamic efficiency. It has the classic Olympic swimmer shape--broad shoulders, long front limbs with giant paddles, and huge pectoral muscles. Ridges down the back help it travel straight so it doesn't need to do a lot of sideways sculling. And on top of the ridges are little bumps. Those bumps break surface tension, and allow the body to glide more smoothly through water. Leatherbacks are also very well insulated with fat, and have the perfect shape for heat retention. So they can dive very deeply or swim in frigid water. The turtle's diet is mostly jellyfish, which is high in protein. Leatherbacks convert food into fat and oil quickly, storing enough energy till it finds the next food patch.

3. Leatherbacks are patch feeders. They forage one patch of food after another. Turns out, jellyfish are plentiful by the Eastern U.S. coastline. Therefore, the Florida population did not have to swim across the ocean to find food.

4. They are part of the food web and a vital part of a healthy ecosystem. For example: Leatherbacks eat jellyfish. Jellyfish eat plankton and small fish. An overabundance of jellyfish can depress many fish species. Unfortunately, fishermen are catching and killing leatherbacks which help control the jellyfish population.

5. In the 19th century, sailors on whale and seal hunts took shiploads for food. In the 1950s, farmers introduced goats to the Galapagos islands as an alternative food source. As the goat population boomed, they out-competed tortoises for vegetation.

6. There were once 14 Galapagos tortoise subspecies. Three have gone extinct. Lonesome George may be next because he's the only remaining member of his species.

Resources

For more about the Charles Darwin Research Station and their work on giant Galapagos tortoise restoration, visit: www.darwinfoundation.org/Restoring/index.html

Students can learn more about the plight of sea turtle species at Sea Turtle Restoration Project's Web site: www.seaturtles.org

For an informative and entertaining read, try out this book. Turtles, Tortoises & Terrapins, by Ronald Orenstein, Firefly Books, 2001

RELATED ARTICLE: Last of his kind.

Tough-bodied bachelor--102 cm long, weight 88 kgs--seeks vegetarian lady to keep bloodline going. Enjoy sleeping, eating, and lounging in pool.

Lonesome George is desperate for a mate. He's one of the 14 subspecies of giant tortoises indigenous (native) to the Galapagos Islands west of Ecuador. Three subspecies have already gone extinct. George, the sole representative of his kind, could be next.

Over 250,000 tortoises once roamed these islands. "They were everywhere," says herpetologist Cruz Marquez of the Charles Darwin Research Station (CDRS). But in the 19th century, tortoise populations tumbled when sailors on whale hunts captured shiploads for food. Then, fishermen and farmers in the 1950s introduced goats to the islands to serve as an alternative food source. As the goat population boomed, they beat out tortoises for vegetation. Today, about 50,000 tortoises remain--an endangered species.

When scientists combed Pinta Island in 1971, they found George alone. Today, the bachelor shares a stonewalled corral with two female tortoises from Isabela Island at the CDRS. The station runs a tortoise captive-breeding program on Santa Cruz Island. Scientists hoped George would pass on his genes via these closely related females. "He chases them," says Ros Cameron of the CDRS. While some mating has occurred, no eggs have been produced.

Why? Theories abound, from sexual dysfunction to genetic differences. Zoos have been combed to find a closer match for George, but no daters seem available. Cloning has been proposed, but the technology is deemed too premature. Could scientists have missed spotting a female on George's native island? They hope so. While the CDRS has successfully released more than 3,000 captive-bred tortoises back to their home islands, George is still lonesome.