Sea Turtles

06

Canaveral National Seashore serves as an important nesting area for sea turtles. During the months of May through August, giant sea turtles lumber ashore to nest on the beach. Three species are known to nest within the park: the loggerhead, leatherback and green sea turtles. Loggerheads lay 3,000-4,000 nests per year. Up to three hundred greens and only a few leatherbacks deposit their eggs within the park boundaries each nesting season.

The sea turtles lay approximately 100 round, white, leathery eggs in each nest. Prior to 1984, most of the eggs laid within the seashore were eaten by raccoons, and to a lesser extent by ghost crabs. Some nests are lost when beaches erode during storms.

If the eggs survive, they begin to hatch in about sixty days. The first turtles to hatch will wait until their nest-mates have left their eggshells. Because of the depth of the nest, it would be difficult for one three-inch hatchling to emerge from the eighteen-inch deep nest by itself. There is also safety in numbers. When the cool sand signals the safety of nighttime, the hatchlings gradually dig their way out of the nest in a united effort to make their way to the sand’s surface.

Many hazards await the hatchlings when they reach the surface of the nest. Ghost crabs, birds, raccoons and the drying heat of the early morning sun are waiting for the tiny turtles as they try to make it to the ocean.

Once the turtles make it past the surf, they swim to a region of the Atlantic Ocean known as the Sargassum Sea, a large area of seaweed which drifts with the ocean currents. Here the hatchlings feed on seaweed and tiny animals and seek protection from predators. When they reach adolescence, some turtles return to the inshore waters of Mosquito Lagoon.

The ocean holds more hazards than just the sea turtles’ natural predators. Many deaths are attributed to entanglement in fishing lines, collision with ships and boat propellers, drowning in commercial fishing nets and ingesting plastic fragments or congealed oil.

Research on the Park

In the early 1980’s, researchers found raccoons were destroying 98 percent of Canaveral’s turtle nests. The park began a program to help reverse this trend. After experimenting with several different ways of protecting the eggs, park rangers found that by securing a wire mesh screen over the nest, raccoons were prevented from digging into the nests. The small hatchlings could still exit the nest through the openings in the mesh. During the months of May through August, park rangers and volunteers work each night to screen the nests. After two months, when all the eggs have hatched, the screens are removed and one of every ten nests IS excavated to monitor the success rate. Over 80 percent of the turtle nests have been protected using this method.

YOU Can Help

1. Possessing turtle parts is illegal. Leave any dead sea turtle you may find undisturbed. Write down where you found the turtle and, if it was tagged, the number, color and type of tag. All sea turtles are classified as either threatened or endangered species, and are protected by federal law. Moving a carcass or removing pa~ts from one is prohibited by the Endangered Species Act. If the turtle was found in Canaveral National Seashore report the finding to the Information Center or Ranger Station, or call (904) 428-3384 or (407) 867-4077. If found outside the park, call the Florida Marine Patrol at (407) 383-2740 or 1-800-342-5367

2. Canaveral National Seashore is closed at night, but should you encounter turtles on a beach outside the park, turn off flashlights and car lights and do not interfere with the turtle’s activities. If a sea turtle is disturbed, it will not nest.

3. Attend a conducted program or a nighttime Turtle Watch” to learn more about sea turtles. Turtle Watches take place at night in June and July. Ask a park ranger for details.

1. THE GREEN TURTLE

by BLAIR E. WITHERINGTON

V18#1 1989 Underwater Naturalist

Witherington is a doctoral candidate in zoology at the University of Florida, Gainesville, and is currently studying the behavior of hatchling sea turtles at the Archie Carr Center for Sea Turtle Research Photos courtesy of the Center for Environmental Education. Washington, DC.

Few reptiles have influenced man’s culture, inspired his curiosity, and roused his admiration more than the green turtle. Though this turtle’s beauty and mysterious nature may prompt romantic prose, it is the utility of its body parts which has given it the dubious distinction of being the world’s most important reptile.

The use of the green turtle as food has both cultural and historic implications. European sailors first exploring the Caribbean found an abundance of green turtles. Sighting of vast green turtle “fleets,” containing thousands of animals presumably on nesting migrations, were commonplace. Adults nesting on beaches in the Cayman Islands and the Greater Antilles were readily harvested. The hearty animals were stored alive for weeks on their backs in the holds of ships. They soon became a mainstay of fresh meat for European sailors, thereby facilitating the exploration and colonization of the Caribbean.

In modern times, the green turtle and its eggs continue to be valuable sources of protein for many coastal subsistence cultures. In many cases, centuries of tradition surround the capture and use of these animals. Apart from their nutritive value, green turtles have also played a part in folklore, touted as sources for various medicines and aphrodisiacs.

Many developed countries tend to view the green turtle primarily as a source of valuable luxury products. Perhaps the most renowned of which is the clear broth made from the fatty cartilaginous tissue attached to the animal’s upper and lower shell. These tissues, individually called calipee and calipash, are typically surrounded by a green fat from which the turtle takes its name. Other common names such as “soup turtle” and “edible turtle” reflect the special culinary regard held for the green turtle. Cosmetic oils, fine leather products, and stuffed whole animals complete the list of luxury products.

The green turtle is a splendidly handsome animal. The head is smoother and more rounded than in other sea turtles. Its carapace is oval-shaped with a slight posterior tapering, moderately domed, and covered with smooth non-overlapping scutes or plates. Hatchlings are roughly two inches in shell length and weigh about one ounce. The soft carapace and most of the upper surface is typically a solid blue-black. Thin white margins on the trailing edges of the front flippers and the cream white underside contrast sharply.

The soft carapace hardens with growth and develops a light, chocolate brown coloration that spreads from the center of each carapace scute. By the time the animal is the size of a dinner plate, a pattern of radiating streaks originating within each of these scutes can be clearly seen. Shades of yellows, browns, greens, and black in the pattern vary among individuals.

Green turtles are the largest of the shelled sea turtles, growing to about three feet in carapace length and 250 pounds. Historical accounts report adult weights of over 600 pounds, but few contemporary adults weigh much over 400 pounds.

Adult shell coloration varies both between and within populations. The bright, radiating lines of the juvenile pattern may remain or fade into a buff, grey, or olive tone, often with scattered dark spots.

If the green turtle’s appearance is considered dainty, then so might be its temperament. When captured, green turtles seldom thrash wildly or attempt to bite. A few minutes after being boated, green turtles are placid and submissive, unlike their loggerhead, hawksbill, and ridley cousins. In the water green turtles are generally shy. offering divers only fleeting glimpses.

The green turtle, Chelonia mydas. shares its genus, Chelonia, with a closely related turtle from the eastern Pacific, the black turtle (Chelonia agassizi). Although the species status of the black turtle may be the subject of taxonomic dispute, the distinctness of its population is clear. Black turtles, as their name suggests, are darkly pigmented on both top and bottom. The adults are considerably smaller than green turtles, and they lay smaller complements of eggs.

Green turtles are powerful, swift swimmers, but despite their aquatic grace, they are, like all sea turtles, awkward on land. Green turtles leave the sea to nest on sandy beaches. They move with a sort of butterfly stroke gait using all four flippers simultaneously. This gait differs markedly from the alternating limb movements typical of terrestrial quadrupeds and most other sea turtles.

Most of what is known about green turtle life history has been pieced together from information gathered on nesting beaches when the turtles return to the terrestrial environment, dig nests, deposit their eggs and conveniently place themselves within the reach of scientists. But only a small portion of the turtle’s life is spent on a nesting beach. Biologists wishing to conduct a complete study of green turtle ecology are limited by the physical barriers that the vast oceans present.

For the most part, studies on the aquatic lives of green turtles has taken a “black box” approach. One indirect yet useful technique is a turtle-tagging program. Nesting green turtles are easily tagged. The tags are commonly attached to the turtle at the trailing edges of the front flippers and are engraved with an identifying code and the tagger’s return address. Like messages in bottles, tags may be recovered later at the same beach or elsewhere. Comparisons of information gathered from tagged and recovered green turtles serve as clues to their oceanic biology.

On the eastern shore of Costa Rica near the village of Tortuguero lies a stretch of beach that is the major green turtle nesting site in the Caribbean. Tagging of nesting green turtles has continued there for more than 30 years. Most of what is known about green turtle reproduction and adult life history was gleaned from the investigations of Archie Carr and his students on this remote Costa Rican beach. Among the first revelations was the great fecundity. or reproductive potential, of green turtles. During the nesting season, a female green turtle may deposit as many as seven clutches of from 60 to 160 eggs. spaced by intervals of about two weeks. Following this great expenditure of energy. a female green turtle will skip the next one to three nesting seasons.

Recoveries of tags applied at Tortuguero indicate that female green turtles travel hundreds of miles between nesting and foraging areas. In addition to being extensive, these migrations also appear to be incredibly precise. Green turtles make their landfalls often within yards of the same sites they used in previous seasons. This site fidelity may greatly restrict the genetic exchange between nesting colonies. Although many nesting green turtles have been tagged throughout the Caribbean, no green turtle tagged on another beach has ever been known to nest at Tortuguero, nor has any Tortuguero female been observed nesting elsewhere.

The incubation period of green turtle clutches is roughly two months, depending on ambient temperature. When nearly all the hatchlings in a clutch have emerged from their shells, the little turtles scrape away at the surface of the egg chamber beneath the sand in an orchestrated fashion. This sibling teamwork displaces nearly three feet of sand while the hatchlings make their way up the column dug by their mother. Under cool conditions, typically at night, the hatchlings waiting at the surface of the nest burst from the sand in unison and scramble toward the ocean.

Once in the surf they stroke away from shore along relatively straight paths for miles beyond their sight of land. This pelagic trek marks the beginning of the “lost years,” one of the most enigmatic aspects of green turtle life history. Hatchlings leaving their natal beaches are apparently incorporated into pelagic gyres

that may span entire oceans. Within these gyres, colliding surface currents concentrate the small turtles within floating communities of free living and epibiotic animals. The common marine alga Sargassum forms the substrate on which many of these communities depend. Many sea turtle biologists believe that it is this collection of pelagic coelenterates, crustaceans, mollusks, worms, and other invertebrates on which green turtles and other sea turtles feed during their first few years. Unfortunately these same biological fronts tend to collect oil, tar, and other synthetic refuse.

After spending these first few years as a pelagic carnivore, green turtles become vegetarians. At four to eight pounds in weight, juvenile green turtles move to the underwater seagrass pastures that cover the shallows of continental shelves and island lagoons in the tropics where they eat primarily seagrasses and benthic algae. From this point on they remain benthic herbivores. Only manatees and dugongs are larger marine herbivores. In captivity green turtles will feed readily on cut fish and squid. Turtles on such high protein diets grow much faster than their wild counterparts, but may suffer some liver dysfunction in later years.

Adaptations to their herbivorous lifestyle include sharp serrations or “pseudo-teeth” outlining the edges of the lower beak. These serrations slide against grooves in the upper jaw and act as efficient grass clippers. By cropping rather than uprooting seagrasses, green turtles are able to maintain regular feeding areas much like well-kept lawns. It appears this continued cropping improves the nutrient quality of the seagrasses.

Tagging and recapture studies of juvenile green turtle populations reveal that it takes 30 or more years for them to reach sexual maturity. As green turtles approach adult size, they grow much more slowly. Adult females measured repeatedly at nesting beaches over as many as 10 years often show scarcely more than half an inch

of growth in shell length. Because adult green turtles grow so slowly, accurate judgments of adult age based on size are impossible. Although some green turtles may in fact be quite ancient, it is probable that most large individuals simply reached maturity at an especially large size.

The International Union for Conservation of Nature and Natural Resources (IUCN) regards the green turtle as an endangered species. The historical record indicates that many of their unique nesting colonies have been extirpated or have diminished to paltry numbers of individuals. Most of the green turtle rookeries which once provided a seemingly endless supply for the original Caribbean colonists have been virtually eliminated, among these the Cayman Islands, Florida’s Dry Tortugas, Bermuda, the Bahamas, and much of the Greater Antilles.

Although well deserved, the green turtle’s endangered designation should not lead one to believe that this turtle’s numbers are well known. The demographical data necessary to formulate population dynamics models are difficult to obtain. Even if censuses of the world’s populations were complete, it would be difficult to say for sure whether the numbers acquired were adequate for population stability.

Fortunately, those interested in conserving green turtles have not, in the

face of such uncertainty, been hesitant to act on behalf of this species that appears to be slipping dangerously toward extinction. Many nations now regulate or prohibit the taking of adult females on nesting beaches. In some countries the harvest of and trade in green turtles from egg to adult stages are banned. In addition to protection, governments are experimenting with various other conservation programs ranging from shielding nests from predators to rearing hatchlings until they are large enough to avoid predations.

Efforts to conserve green turtle populations are not immediately rewarding. Because of the green turtle’s long generation time, successful conservation practices initiated today will not result in appreciable positive changes in numbers of nesting green turtles for decades to come. Nesting populations in areas where lengthy protection has been afforded, such as the island of Aldabra in the Indian Ocean and Florida’s east coast, are only recently showing optimistic signs of positive growth.

The survival or extirpation of the world’s green turtle populations will depend on the empathy and resolve of both developed and developing nations. The preservation of this truly international and magnificent animal will prove to be a challenging and worthwhile endeavor.

THE LEATHERY TURTLE

by KAREN and SCOTT ECKERTThe authors received doctorates from the University of Georgia. Their doctoral research was conducted on leatherback turtles on St. Croix, U. S. Virgin Islands. They work at Scripps Institute of Oceanography, La Jolla, CA. Scott took all the photos but one.

The leatherback sea turtle, known to scientists as Dermochelys coriacea, is the sole surviving species of the family Dermochelyidae. Arguably the most oceanadapted of all the sea turtles, the leatherback boasts several unique morphological features. Powerful front flippers, spanning 6.5-8 feet, are ideal for pelagic existence where endurance to traverse vast expanses of open ocean is the key to survival. In contrast, other sea turtle species, all members of the family Cheloniidae, are best described as littoral in their ecology. They have bony shells and their front flippers are proportionally shorter than those of the leatherback, allowing chelonids the advantage of quick, acrobatic movement. Skillful maneuvering is important in shallow water where foraging can entail exploring the crevices of a reef or rock ledge, and where predator escape requires an instant response.

The most notable feature of the pelagic leatherback is its streamlined form. Broad shoulders, a strongly tapered carapace, and seven dorso-longitudinal ridges serve to enhance laminar flow. The leatherback is sheathed in leathery dermis rather than a rigid bony shell. This characteristic gives the turtle its name "dermo chelys," or "skin turtle." Streamlining and bone reduction allow these 600-1200 pound giants to glide through the water with minimal resistance. Popular names, such as "trunk," "coffin-back," and "keelback," reflect its unique body form. The leatherback's uniqueness is more than skin deep, however. The carapace, rather than being held rigid by fused ribs, is supported internally by a mosaic of small bones linked together like a jigsaw puzzle and embedded in tough, oil-saturated connective tissue. The ribs lie underneath this mosaic and are not flared appreciably nor fused together. The plastron, or belly plate, consists of eight narrow bones joined in a broad open ring and embedded in thick dermal tissue. The somatic skeleton shows more cartilage than other sea turtles and is theoretically more flexible. Clearly this streamlined, smooth-skinned, flexible turtle is quite unlike its armored tank cousins.

All these modifications make sense when one remembers what a leatherback does for a living. Ranging the world's oceans in search of a bizzare diet of jellyfish, there is little need for the protection that bony shell confers against abrasion. Hydrodynamic form is much more important. In addition, internal flexibility may be requisite for deep diving. We have recorded gravid leatherbacks diving to depths exceeding 3200 feet in the Caribbean Sea. Pressures at this depth is profound: almost 1500 pounds per square inch. It would be difficult to build a rigid body form that would not be crushed by these great pressures, yet retain the streamlining essential for energetically efficient long-distance swimming. By flexing under external pressure, leatherbacks appear to have adopted the same strategy as deep diving marine mammals.

Leatherbacks rarely, if ever, rest at sea. This incessant movement may be important for survival in the wild, but it is a disappointment for scientists who would like to keep leatherbacks in captivity. Husbandry techniques have yet to be successful. Leatherbacks, even tiny hatchlings, swim against the walls of confinement and often fatally injure themselves. In light of all that has been said, it is not surprising to learn that leatherback nesting beaches are chosen as much for their offshore characteristics as for their terrestrial amenities. Since offshore reef and rock would abrade or seriously injure the turtles as they attempted to land, favored nesting beaches, such as those in Mexico, Sri Lanka, Indonesia, South Africa, French Guiana, and the West Indies, are flanked by unobstructed, often deep, ocean.

Nesting presents many challenges for sea turtles. Predation risk, elevated body temperature, and fatigue characterize the terrestrial sojourn. Strong, slender flippers confer freedom and grace in the ocean but are poorly suited for beach crawling. Gravid leatherbacks use a heaving "breast-stroke" to propel themselves forward at a labored pace of 10 feet per minute. Since they lack reverse gear, a female nesting in French Guiana or eastern Australia can find herself mortally trapped in a thicket of driftwood as she slowly hauls her huge bulk back to the sea. There are other problems. Light reflected from an inland swamp or mangrove lagoon can disorient a nesting female (and later her hatchlings) and lure her away from the sea. Heavy predation or erosion can reduce the chance that eggs will incubate to term. For these and other reasons some beaches prove more successful than others. It is widely believed

that a turtle returns as an adult to nest on the beach from which she herself was hatched. In this way, those beaches most successful in producing baby sea turtles will be favored by the next generation. Thus, over time, beaches poorly suited for leatherbacks for reasons of high predation, dangerous surf or confusing lagoons, are weeded out of the species' collective memory simply because the turtles that nested there did not survive, or did not leave surviving offspring.

Leatherbacks commonly nest every two or three years. The nesting season is a lengthly one, spanning March to Julythroughout most of the Caribbean and October to February along the Pacific coast of Mexico and Central America. During any particular year, gravid females arrive at the nesting beach asynchronously throughout the first three months of the nesting season. It is not intuitively clear why this is so; one would expect turtles to arrive as early as possible in order to have time to lay as many clutches as possible. Leatherbacks sometimes run out of nesting season before they run out of eggs, as attested by females who have stranded in northern latitudes (presumably returning from a summer in the tropics) with oviducts full of shelled eggs. There are several theories as to why some females do not begin nesting until the middle of the nesting season. One is that females embark from widely separated areas and require varying lengths of time to complete the journey. Another contends that the migration is initiated only after the female accumulates a threshold level of fat necessary to sustain both the journey and the nesting season.

We have no answers to this puzzling pattern of arrival, but it is interesting, in this high-tech age, that one of the most useful tools available to us may turn out to be that familiar little hitch-hiker, the barnacle. These "living tags," picked up through successive latitudes, offer clues about the general direction of migratory movement. Our studies of barnacles on leatherbacks nesting at Sandy Point National Wildlife Refuge, St. Croix, U.S. Virgin Islands, suggest that the majority of the nesters embark from temperate latitudes. Once nesting commences, gravid females cycle independently of one another. Each returns to the beach approximately every 10 days to deposit another clutch of eggs and deposits as many as 10 clutches in a single season.

Nesting is typically nocturnal. Once ashore, a nest site is chosen, and the rear flippers are used to excavate an egg chamber. During this process, one flipper and then the other scoops the sand. As the flask-shaped cavity nears completion, it is as deep as the flippers can reach. Since these flippers are strongly modified for ruddering in the open sea, one cannot help but marvel at how well they perform their adopted task. As the flipper reaches slowly, deliberately, to the bottom of the nest for the next scoop of sand, it articulates just as a human hand would do in the same position. It scoops, cups the sand, and curls upward to avoid spilling the load. Each load is carefully dumped at the nest rim, then expertly flung over the carapace to preclude its sifting back into the nest. An experienced field biologist can tell at a glance the stage of the nesting cycle by the pattern of discarded sand saddling the female's carapace.

When the cavity is complete (25 - 30 inches deep and 10 inches wide), the female rests with one rear flipper poised over the nest. One imagines that this posturing evolved to shield the eggs from rain and obscure them from waiting mongooses, coati mundis, and other predators. Within seconds, the eggs drop into the nest. One, then two, and three at a time. After all the preparation, the main event is over in less than nine minutes. Fifty to 120 glistening, white eggs come to rest gently against one another. These leathery, soft eggs are larger than those of any other sea turtle. Their diameter is consistent across populations and averages about two inches. The clutch also includes as many as 40 or 50 smaller, often misshapen, yolkless eggs. The function served by the yolkless eggs is unknown. The leatherback is the only turtle that lays so many nonviable eggs.

The eggs are covered and left to incubate in the warmth of the sun. They are highly dependent on favorable outside conditions for development. Temperature is one of several crucial environmental parameters. It determines incubation duration, affects moisture regimes and, when too high or too low, can cause deformity or death of the tiny embryo. Perhaps the most interesting aspect of thermal ecology in sea turtles is that the sex of the baby turtle will be determined predominantly by the temperature at which the egg incubates. A shift of less than one degree during the critical period (believed to be the middle trimester of the two-month incubation) can bias sex ratios toward one sex or the other. Warmer temperatures result in more female hatchlings, cooler temperatures in more males. The pivotal temperature, that temperature at which the clutch contains both males and females in roughly equal proportions, has been reported to fall between 29 and 30 degrees C for leatherbacks. Much research remains to be done in this area of sea turtle ecology: Are pivotal temperatures consistent among nesting beaches in different parts of the world? Do females "choose" nesting sites to optimize sex ratios? Does the conservation practice of moving eggs to hatcheries and beach zones safe from erosion and predators alter natural sex ratios? What are the "natural" population sex ratios for hatchlings, juveniles, adults?

The likelihood of answering these questions is slim until a way can be found to sex hatchlings without sacrificing them. To complicate matters, juvenile leatherbacks mysteriously disappear during their developmental years, and the adults are not seen anywhere consistently except on the nesting beaches. Although it is certain that nesting turtles are females, this does little to address the question of what proportion of the population at large is female, and what proportion is male.

Males are as enigmatic as juveniles. In some areas such as Pacific Mexico, males are regularly observed among females in the waters adjacent to the nesting beach. In other parts of the world such as the insular Caribbean, the females appear to arrive alone. In any event, there is no way of knowing what proportion of the population at large has journeyed to the nesting grounds.

These and other questions highlight the need for expanded pelagic research. A new generation of remote sensing equipment, more compact and affordable than ever before, promises to shed light on pelagic behavior. Satellite transmitters and microprocessor-controlled depth recorders are the wave of the future. We recently deployed several remote timedepth-recorders (TDRs), developed for use on marine mammals by Dr. Gerald Kooyman of Scripps Institution of Oceanography, in an effort to gather information on the diving behavior of leatherback turtles off their nesting beach at Sandy Point, St. Croix. The turtles turned out to be remarkable divers, averaging three dives per hour, both day and night. Submergence time per dive averaged 12 minutes, considerably shorter than what would have been predicted from previous studies with the smaller chelonid sea turtles which averaged about 30 minutes per dive. However, maximum dive depths were far beyond anything we could have imagined averaging 200 feet, but some exceeded 3300 feet. Equally interesting was the difference in day and night diving patterns. Day dives were typically deeper, longer and less frequent than night dives. Turtles spent more time on the surface during the day, and dive depths were much more variable during the day.

It is not clear why leatherbacks make frequent and robust dives, but we believe they may be foraging. In the tropics, jellyfish are scarce at the surface, but siphonophores and other cnidarians are often associated with a zone of deep-sea biological life called the Deep Scattering Layer (DSL). The DSL is actually a series of zones where zooplankton are concentrated and which reflect and scatter sonic signals. These zooplankters make a rapid vertical migration to the surface at dusk and return to depth (usually below 2000 feet) at dawn. Since the turtles dive more shallowly and more consistently during the night than during the day, they may be foraging within the risen DSL. It is also possible that feeding is not the sole impetus for the diving. Since leatherbacks spend most of their lives in cooler temperate waters, deep diving may serve to lower body temperatures while in warm tropical latitudes. In addition, the really exceptional depths may have been precipitated by predator encounters.

Information about behavior on a larger scale, such as the post-reproductive movement of females leaving the nesting beach, is scant. One adult female traveled some 600 miles north to Mozambique after nesting in Tongaland, Natal. Leatherbacks first tagged while nesting in the Caribbean (Sandy Point, St. Croix; Silebache, French Guiana) have stranded as far north as New Jersey. Similarly, an individual nesting in Trinidad later stranded on Rockaway Beach, New York, and a female tagged in Tortuguero, Costa Rica, was subsequently caught in Cuba. The most spectacular movement was by a leatherback tagged while nesting in Suriname and recovered less than a year later off Ghana, West Africa. The intervening distance, at least 3700 miles, is the longest migration on record for any reptile. Nonetheless, information directly relevant to navigational systems, routing, and impetus is lacking.

Scientists and wildlife managers are increasingly frustrated by these large gaps in our knowledge about migratory patterns and life history characteristics. Today there are very few places left where leatherbacks nest in any numbers, notably Pacific Mexico, Malaysia, and French Guiana. Many beaches, in the Caribbean and elsewhere, have been irreparably degraded by development. Some nesting populations have been harvested to extirpation. Many of the most serious threats to the turtles' survival have been identified, but it continues to be difficult to develop management and recovery plans for an animal about which we know little save what occurs in the "maternity ward." Leatherbacks were declared endangered by the United States Department of the Interior in 1970 under the Endangered Species Act. Then, in 1975, they were listed under Appendix I of the Convention on International Trade in Endangered Species (CITES).

The former ruling translates into a commitment by the United States government to set aside and protect areas deemed critical to the survival of the species. Sandy Point National Wildlife Refuge in the U.S. Virgin Islands is an important nesting grounds for leatherbacks and is protected for this reason. The law also prohibits harrassment or harm and makes it a felony to sell, buy, or possess a leatherback turtle (or any part thereof). The Center for Environmental Education in Washington D. C. is working hard to convince all wider Caribbean nations to join CITES and to halt the enormous trade (primarily to Japan) in sea turtle products emanating from the Caribbean region.

Fortunately, international trade, so devastating to hawksbill and green sea turtles, has never been a serious threat to the leatherback. Thick yellow oil, rendered from the greasy carapace, is touted as an aphrodisiac in some parts of the Caribbean, but is more commonly used as a chest rub to relieve congestion. In Arabia and India it is used to treat boat timbers. It is rarely exported. Though eggs and meat sometimes find their way

across international borders in Latin America and Southeast Asia, the harvest is more often for local community or subsistence use. But even local harvest can be damaging if uncontrolled. In the British Virgin Islands, for example, leatherbacks have been hunted for generations. Only in 1986, when the total number of leatherbacks arriving to nest had been reduced to fewer than five turtles, did the species receive protective legislation.

In the British Virgin Islands, as in many parts of the world, "turtling" is a tradition shaped by legend and mysticism. Local turtle fishermen know that a leatherback is coming ashore when they see a turtle-shaped apparition in the clouds which "points" to the chosen beach. On the beach the men report unexplained noises in the bushes, sticks breaking, whistling, strange odors, and the ghosts of deceased fishermen just prior to the turtles' emergence. Once ashore the unfortunate nester is flipped on her back, a position from which she cannot recover. Her front flippers are tied together. In the morning light, the fishermen dismember her, dividing the meat among their neighbors and rendering chunks of carapace and cartilage into oil in large copper caldrons. The eggs are removed. There is no waste. A similar situation exists on the remote beaches of Guyana where Amerindians harvest virtually every leatherback that comes ashore. However, in Guyana, despite the continued harvest, there is no evidence that the leatherbacks are declining. It may be that the patterns and mechanisms of recruitment are different for continental nesting populations than they are on a small island. We simply do not know.

In most parts of the world the leatherbacks are not killed directly, but indirectly. Nesting habitat is destroyed by coastal development and other "improvements," including jetties, harbor dredging, and heavy recreational use. This global trend affects not only sea turtles, but also sea birds and nearshore benthic systems (coastal marshes, seagrass beds, mangrove forests, coral reefs). Nor is the open ocean spared. At-sea dumping of waste is an enormous and growing problem. Leatherbacks are stranding from New Jersey to California with their intestines packed with plastics, which they apparently mistakenly ingest as jellyfish. Long-lines, drift nets, and trawls snag and drown the turtles, along with countless millions of non-target finfish, sea birds, and cetaceans.

These are not remote and distant problems. The thoughtful observer will conclude that the leatherback sea turtle is threatened by the same forces with which we are threatening ourselves: poisoned oceans, careless development, an abundance of garbage. Global extinctions are on the rise. Some say it is a necessary price to pay. Others believe that man's extinction is inevitable when the oceans and forests, and the creatures that live there, are gone. Sea turtles and men are linked in a continuous progression of life. As sea turtles decline, we cannot help but lose a part of ourselves. And, as the American naturalist William Beebe has said, "When the last individual of a race of living things breathes no more, another heaven and another earth must pass away before such a one can be again."

Readings on Sea turtule.... 1. SEA TURTLES

INTRODUCTION

Sea turtles are highly migratory and ply the world's oceans. Under the Endangered Species Act, all marine turtles are listed either as endangered or threatened . The NMFS has authority to protect and conserve marine turtles in the seas, and the U.S. Fish and Wildlife Service maintains authority while turtles are on land.

The Kemp's ridley, hawksbill, and leatherback turtles are listed as endangered throughout their ranges. The loggerhead and olive ridley turtles are listed as threatened throughout their U.S. ranges, as is the green turtle, except the Florida nesting population which is listed as endangered.

SPECIES AND STATUS

The Pacific species are loggerhead, green, leatherback, hawksbill, and olive ridley turtles. All are also found in the Atlantic Ocean, but the olive ridley does not commonly enter U.S. waters. In Hawaiian waters, the green and hawksbill are most abundant. Off the U.S. west coast, the loggerhead, leatherback, and olive ridley turtles are most commonly reported.

Historical data on sea turtle numbers are limited. In addition, the length of time that data have been collected has been short when compared with the long life and low reproductive rate of all turtle species. It is difficult to assess the long-term status of sea turtles due to the limited data.

The estimated number of female loggerheads nesting annually in the southeastern United States is about 20,000-28,000. Most nest along Florida's east coast where nest numbers have been stable for 5 years. Only about 700-800 female Kemp's ridley turtles nest annually along a limited portion of Mexico's Gulf coast. In 1947, on a single day, 40,000 females were seen nesting on one beach alone. The documented decline in the Kemp's ridley is probably indicative of similar population trends for other sea turtles, though the periods of their various declines may have differed.

Historically, the green sea turtle has supported large fisheries along the Florida and Texas coasts, although its nesting on U.S. beaches has probably always been limited. Currently, perhaps 400-500 green turtles nest annually along the Florida coast. There are no historical estimates for the numbers of hawksbill or leatherback turtles nesting on U.S. Caribbean beaches. The hawksbill has been heavily exploited, and continued trade of products from this species suggests that further declines are possible. The trend over time of the leatherback turtle in U.S. waters is unknown.

Since 1973, Hawaiian surveys of green turtles indicate that the estimated number of turtles nesting annually is about 450-475, and that it is gradually increasing. No accurate historical record of this green turtle population exists. The Hawaiian hawksbill turtle population is very small; only 12-15 nests are recorded each year. In Hawaii, little is known of the species' reproductive biology or population trends.

ISSUES

Bycatch and Multispecies Interactions

In the North Pacific there were concerns about sea turtle deaths in the recently concluded high-seas driftnet fisheries. Turtle bycatch rates were monitored on driftnet vessels by U.S., Canadian, Japanese, Korean, and Taiwanese scientific observers. The effect of these driftnet fisheries on U.S. sea turtle populations is unknown, but a moratorium on high-seas driftnet fisheries is now in place under a United Nations resolution.

Turtles are also killed incidentally in various commercial fisheries. Turtles are caught and killed in pelagic longline fisheries targeting tunas and billfishes. Conservatively, as many as 11,000 sea turtles may have been killed annually in offshore shrimp trawls. Turtle mortality from inshore shrimp trawling was not estimated. Fortunately, turtle excluder devices (TED's) have been developed for shrimp and fish trawls. TED's enable turtles to escape the trawl net and prevent them from drowning. These devices reduce the turtle kill by shrimp trawls by 97% and studies indicate that the use of TED's minimally reduces shrimp catches. TED use is presently mandated for most of the Atlantic and Gulf of Mexico shrimp and summer flounder trawl fisheries.

Habitat Concerns

Coastal development is reducing nesting, egg incubation, and foraging habitats. Floating tar balls and plastics, if eaten, can harm or kill sea turtles. The magnitude of these problems is not fully known, but they occur worldwide, and international cooperation for marine turtle protection and recovery is required.

Progress

Pacific: The recovery of endangered and threatened marine turtle populations in the North Pacific will be enhanced by the United Nations-sponsored moratorium on large-scale driftnet fishing that went into effect on 1 January 1993. During 1990 and 1991, when the high-seas driftnet fisheries were carefully monitored by NMFS and cooperating foreign fishery agencies, data were collected that have led to a better understanding of the pelagic distribution and ecology of sea turtles in the North Pacific.

In the Hawaii pelagic longline fishery for tuna and swordfish, the incidental catch of turtles is being closely monitored through a compulsory logbook program. A scientific observer program is being considered as a means to collect the more detailed data required to verify logbook reports and assess turtle impacts. During late 1993, a workshop was held to formulate research techniques to determine hooking and entanglement mortality of turtles incidentally caught by longline.

Significant progress is being made in the monitoring of Hawaiian green turtles. In 1992, a 5-year series of saturation surveys was completed at East Island, French Frigate Shoals, the principal location of Hawaiian green turtle nesting, by NMFS and the U.S. Fish and Wildlife Service. Based on these surveys, rigorous quantitative methods have been developed for annual nesting surveys at East Island. Progress is also being made in monitoring juvenile and subadult Hawaiian green turtles in their nearshore habitat. A vigorous research program is underway to study the origins and effects of fibropapilloma tumor disease in the Hawaiian green turtle population; progress has been made in developing information relevant to potential etiologies involving cardiovascular parasites, viruses, and environmental pollutants. A similar disease situation exists among green turtles in Florida and the Caribbean. Atlantic: The joint NMFS/USFWS Atlantic Sea Turtle Recovery Plans have been developed, finalized, and approved. These plans prioritize turtle research requirements and delineate reasonable actions which are believed to be required to recover and/or protect the species.

A major factor affecting the recovery of turtle populations is the mitigation of commercial fishing/sea turtle interactions. The incidental capture of sea turtles in various commercial fisheries has been studied and summarized and was the focal point of a meeting at the recent 13th Annual Sea Turtle Symposium. Recent legislation has allowed NMFS to use observers in selected fisheries to document the occurrence of incidental turtle captures. Also, several new TED models have been recently tested and approved for commercial use, and research continues on the development of a new TED design which would accommodate small inshore turtles.

Considerable progress has been made concerning inshore juvenile developmental habitat research and remote sensing. NMFS research projects have been started on juvenile ridleys and greens in the Cedar Keys and Biscayne Bay, Florida, and in the northwestern Gulf of Mexico. Additionally, a comprehensive research project concerning the incidence, etiology, and epidemiology of fibropapilloma tumor disease in Atlantic green turtles has been started. Concern is growing that this disease may seriously affect the recovery of world-wide green turtle populations.