Nature and Environment Education - SEA TURTLE
Rarely seen around Bonaire:
Leatherback - Driekiel
- very large
- keeled carapace
- black and white body
- open water only
Occasionally seen around Bonaire:
Loggerhead turtle - Kawama
- massive head
- reddish-brown color
- only adult are usually seen around Bonaire
Olive ridley - Warana
- smallest sea turtle,
max length 70 cm
- over 6 lateral scutes
- light gray color
Most often seen on Bonaire reefs:
Hawksbill turtle - Karet
- beak-like face
- overlapping scutes
- serrated edge of carapace
- yellow underside
Green turtle- Turtuga blanku
- round face
- tightly joined scutes
- smooth edge of carapace
- white underside
Why Protect Sea Turtles?
Sea turtles evolved millions of years ago, but today they are threatened with extinction. Populations are declining worldwide due to persistent sea turtle fishing, increased coastal tourism and marine pollution. Nearly all Caribbean populations are severely depleted. Their survival depends on us.
Bonaire's Sea Turtles
Sea turtle species found in Bonaire include the hawksbill, loggerhead and green turtle. Juvenile hawksbills and green turtles can be seen feeding in coral reefs and on sea grass beds. Adult hawksbills and loggerheads lay their eggs on the island's beaches each year and occasionally, a giant leatherback turtle is encountered in Bonaire waters. The capture of sea turtles is prohibited on Bonaire, as is the buying and selling of sea turtle products like shells, meat, eggs and jewelry. Convicted violators can be fined up to Nafl. 5000,-.
Green turtle (Chelonia mydas; local name: turtuga blanku). Olive brown shell often streaked. Underside pale, carapace smooth, rounded jaw. Adults 95-125 cm shell length, feeds on sea grasses.
I Scientific classification
II Habitat and distribution
III Physical characteristics
V Adaptations for an aquatic environment
VII Diet and eating habits
IX Hatching and hatchlings
X Longevity and causes of death
I Scientific Classification
A. Class Reptilia.
1. Reptilia are a class of ectothermic (cold-blooded) vertebrates that includes snakes, lizards, crocodiles, and turtles.
2. Reptiles have scaly skin, breathe air with lungs, and have a three-chambered heart.
3. Most reptiles lay eggs, although some produce eggs that hatch internally.
B. Order Testudines.
This order includes all turtles and tortoises. It is divided into three suborders: Pleurodira (side-necked turtles), Cryptodira (all other living species), and Amphichelydia (extinct species).
C. Suborder Cryptodira.
This suborder includes freshwater turtles, snapping turtles, tortoises, soft-shelled turtles, and sea turtles.
Most scientists recognize two families of sea turtles:
1. Family Cheloniidae are sea turtles with shells covered with scutes (horny plates).
2. Family Dermochelyidae are scuteless turtles with only one modern species, the leatherback turtle. Leatherbacks are covered with leathery skin. They are the only marine turtle whose backbone is not attached to the inside of the shell.
E. Genus, species.
Most scientists recognize eight species of sea turtles:
1. Green Chelonia mydas
2. Black (also know as Eastern Pacific green turtle) Chelonia agassizii
3. Loggerhead Caretta caretta
4. Kemp's ridley Lepidochelys kempii
5. Olive ridley Lepidochelys olivacea
6. Hawksbill Eretmochelys imbricata
7. Flat back Natator depressus
8. Leatherback Dermochelys coriacea
F. Fossil record.
1. The first turtles appeared during the Triassic period, 245 to 208 million years ago.
2. The earliest known sea turtles appear in the fossil record in the Late Jurassic period, 208 to 144 million years ago. Scientists believe that modern sea turtles are derived from marsh-inhabiting ancestors that lived during the Late Triassic period.
3. Fossil records show that the now-extinct sea turtle Archelon ischyros, from the Late Cretaceous period, 144 to 65 million years ago, was one of the largest turtles that ever lived and reached a length of 3 to 4 m (9.8 - 13 ft.).
4. Together with saltwater crocodiles, marine snakes, and marine iguanas, sea turtles are the only surviving seawater-adapted reptiles.
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II Habitat and Distribution
Sea turtles are found in warm and temperate seas throughout the world.
Adults of most species are found in shallow, coastal waters, bays, lagoons, and estuaries. Some also venture into the open sea. Juveniles of some species may be found in bays and estuaries, as well as at sea.
1. Migration habits differ not only among species but also among different populations of the same species. Some sea turtle populations nest and feed in the same general areas; others migrate great distances.
a. Green sea turtle populations migrate primarily along the coasts from nesting to feeding grounds. However, some populations will travel 2,094 km (1,300 miles) across the Atlantic Ocean from the Ascension Island nesting grounds to the Brazilian coast feeding grounds.
b. Black sea turtles migrate along the coast from breeding areas to feeding grounds between the northern and southern extremes of their distribution range.
c. Loggerheads leave foraging areas and travel on breeding migrations that range from a few to thousands of kilometers (1 kilometer = 0.62 miles).
d. Kemp's ridley turtles follow two major routes in the Gulf of Mexico: one northward to the Mississippi area, the other southward to the Campeche Bank, near the Yucatan Peninsula.
e. Populations of olive ridleys have been observed in large flotillas traveling between feeding and nesting grounds in the Eastern Pacific and Indian Oceans.
f. Hawksbill migration studies have been limited. Evidence suggests that some hawksbill populations show cyclic nesting migrations. Other researchers have documented nonmigratory and short-distance migratory populations.
g. Flat backs move from their nesting grounds on the northern coast of Australia and islands to feeding grounds in shallow waters of northeastern Australia. Distance covered ranges from 215 to 1,300 km (134 - 807 miles).
h. Leatherbacks have the longest migration of all sea turtles. They have been found more than 4,831 km (3,000 miles) from their nesting beaches. Migration habits differ among sea turtle species. Migrations may range from a few to thousands of kilometers.
2. The most common method used to track free-ranging sea turtles is flipper tagging. Although this method yields information on migration destinations, it does not reveal travel routes.
3. Recently radio, sonic, and satellite tracking have been successful in monitoring sea turtle movements.
4. Hobbs-Sea World Research Institute has developed a radio transmitter harness for leatherback turtles. Its design allows secure attachment of a transmitter without affecting turtle mobility. The harness was designed to release within several months.
1. Total population figures are often unknown because juvenile and male sea turtles do not come ashore and are difficult to count.
2. Population data are usually based on the numbers of adult females that come ashore to nest. Even then, the numbers are ambiguous - some females nest every two to three years, some may nest more than once on the same beach in a season, and some females will visit more than one nesting beach in a season.
3. Researchers rely more upon the changing numbers of nesting females from year to year to determine population trends of increasing or decreasing numbers. Because broad year-to-year fluctuations in numbers of nesting females make short-term data misleading, surveys of a decade or less may be insufficient to determine a population trend.
a. The Kemp's ridley is the most endangered sea turtle. In 1947, 92,000 nests were estimated. The numbers have been declining dramatically since then. Surveys conducted between 1978 and 1988 indicated an average of about 800 nests per year. Since 1978, the trend shows the number of nests have been declining at about 14 nests per year. The total number of nesting females may be as low as 350 on beaches where tens of thousands of Kemp's ridley used to nest.
b. Nesting populations of green and black sea turtles have not been surveyed long enough for determination of trends. However, qualitative observations during visits over several years suggest a heavy decline.
c. The major loggerhead nesting grounds are located in the southeastern U.S. Population trends of logger heads show a decline in nesting areas of Georgia and South Carolina, but no decline or a possible increase in southern Florida Atlantic areas. More years of nesting data and population biology studies are needed to assess the Florida trends.
d. There are probably several hundred thousand adult female olive ridleys. The olive ridley is the most abundant sea turtle in the world. In 1991, an estimated 610,000 turtles nested in a single week on a beach in India.
e. Very little data are available on hawksbill populations. Estimation of population sizes of nesting females is difficult by aerial assessment: tracks in the sand do not last long and are difficult to see, and nests are often obscured by beach vegetation.
f. Current population numbers for flatback turtles are not known; however, because of its restricted distribution, the flatback is the most vulnerable of all sea turtles to any habitat change or over-exploitation.
g. There are probably less than 115,000 adult female leatherbacks worldwide. There are too few records to predict trends; however, the numbers do not appear to be declining.
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III Physical Characteristics.
Adult males and females are equal in size.
1. Green sea turtles reach about 78 to 112 cm (31-44 in.) and 68 to 186 kg (150-410 lb.). The largest individual collected was 1.5 m (5 ft.) and 395 kg (871 lb.).
2. Black sea turtles reach about 59 to 117 cm (23-46 in.) and 42 to 126 kg (93-278 lb.).
3. The Kemp's ridley and olive ridley are the smallest species, and reach about 55 to 65 cm (22-30 in.) and 30 to 50 kg (66-110 lb.).
The leatherback turtle is the largest sea turtle species; the Kemp's ridley is one of the smallest. Compare their sizes to the size of a human.
4. Loggerheads reach about 82 to 105 cm (32-41 in.) and 66 to 101 kg (146-223 lb.).
5. Hawksbills reach about 53 to 114 cm (21-45 in.) and 27 to 86 kg (60-190 lb.).
6. Flatbacks reach about 81 to 97 cm (32-38 in.) and 60 to 84 kg (132-185 lb.).
7. The leatherback is the largest of all living sea turtles. Mature leatherbacks reach about 1.2 to 1.9 m (4-6 ft.) and 200 to 506 kg (441-1,116 lb.). The largest leatherback recorded was 916 kg (2,019 lb.).
B. Body shape.
Sea turtles are characterized by a large, streamlined shell and nonretractile head and limbs.
1. Depending on the species, sea turtles range in color. They may be olive-green, yellow, greenish-brown, or black.
2. The green sea turtle gets its name from the color of its body fat.
1. A sea turtle cannot retract its limbs under its shell as a land turtle can.
2. Flippers are adapted for swimming. Sea turtles are awkward and vulnerable on land.
3. Fore flippers are long and paddle like.
a. Long digits are fused throughout the flipper.
b. Only one or two claws are present on each fore flipper.
c. A sea turtle swims with powerful wing like beats of its fore flippers.
4. Hind flippers serve as rudders, stabilizing and directing the animal as it swims. The hind flippers of some species are quite dexterous in digging nests in the sand.
1. A sea turtle cannot retract its head under its shell as a land turtle can.
2. Sea turtles have large upper eyelids that provide protection for their eyes.
3. Sea turtles do not have an external ear opening.
4. Like other turtles, sea turtles lack teeth. Jaw shape varies among species. Each species has a jaw shape adapted for its diet.
1. The large, bony shell provides protection from predation and abrasion.
2. In all species except the leatherback, the shell is covered with a layer of horny plates called scutes.
a. Scutes are firm but flexible, not brittle.
b. Scientists can identify sea turtle species by the number and pattern of scutes.
c. The leatherback turtle has a thick and oil-suffused skin, which is an excellent insulator allowing this species to venture into colder waters.
3. The dorsal (top) side of the shell is called the carapace.
a. Depending on species, the adult carapace ranges in shape from oval to heart-shaped.
b. In all species except the leatherback, the bony shell is composed of broadened, fused ribs, and the backbone is attached to the carapace.
c. The leatherback's carapace is composed largely of cartilage raised into prominent longitudinal ridges. A layer of thousands of small dermal bones lies just below the leathery skin.
4. The ventral (bottom) side of the shell is called the plastron.
G. Sexual dimorphism.
1. Male and female sea turtles do not differ externally until they approach maturity.
2. Adult males have longer, thicker tails, because the male reproductive organ is housed in the base of the tail. In males, the tail may extend beyond the hind flippers.
3. On some species, the claws on the fore flippers of males are elongated and curved, which may help in grasping the females' shells during mating.
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Like other reptiles, the sea turtle ear has a single bone in the middle ear that conducts vibrations to the inner ear. Researchers have found that sea turtles respond to low frequency sounds and vibrations.
1. Sea turtles can see well under water but are shortsighted in the air.
2. Under experimental conditions, loggerhead and green sea turtle hatchlings exhibited a preference for near-ultraviolet, violet, and blue-green light.
A sea turtle is sensitive to touch on the soft parts of its flippers and on its shell.
Little is known about a sea turtle's sense of taste.
1. Most researchers believe that sea turtles have an acute sense of smell in the water. Experiments show that hatchlings react to the scent of shrimp. This adaptation allows sea turtles to locate food in murky water.
2. Sea turtles open their mouths slightly and draw in water through the nose, then immediately empty it out again through the mouth. Pulsating movements of the throat are thought to be associated with smelling.
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V Adaptations for an Aquatic Environment
1. Sea turtles are strong swimmers. The cruising speed for green sea turtles is about 1.5 to 2.3 kph (0.9-1.4 mph). Leatherbacks have been recorded at speeds of 1.5 to 9.3 kph (0.9-5.8 mph).
2. Forelimbs are modified into long, paddle-like flippers for swimming.
3. Neck and limbs are no retractile. The shell adaptations necessary for retractile extremities would impede rapid swimming. A sea turtle swims with powerful wing likes beats of its fore flippers.
1. Sea turtles are excellent divers. Leatherbacks routinely dive more than 305 m (1,000 ft.), and they may reach depths of more than 1,190 m (3,900 ft.) seeking jellyfish.
2. Since they are ectodermic, sea turtles have a slow metabolic rate. This slowed metabolism allows them to stay submerged for long periods of time.
a. Hawksbill turtles have been known to remain submerged for 35 to 45 minutes.
b. Green sea turtles can stay under water for as long as five hours. Their heart rate slows to conserve oxygen: nine minutes may elapse between heartbeats.
c. In the north-central Gulf of California, black sea turtles return each year to specific areas. They bury themselves under water in sand or mud and may remain dormant from November to March.
3. During long dives, blood is shunted away from tissues tolerant of low oxygen levels toward the heart, brain, and central nervous system.
4. Leatherbacks have high concentrations of red blood cells; therefore, they can retain more oxygen. The muscle of leatherbacks has a high content of the oxygen-binding protein myoglobin. Myoglobin transports and stores oxygen in muscle tissue.
In studies conducted on green sea turtles, lung capacity exchange in one breath exceeded 50%.
D. Salt secretion.
1. Sea turtles can live in seawater with no need for a freshwater source. They obtain sufficient water from their diet and from metabolizing seawater.
2. Like other marine reptiles and seabirds, sea turtles have a salt gland to rid their bodies of excess salt. This gland empties in the sea turtles' eyes. The secretion of salt and fluid makes them look as if they are "crying" when they come ashore. These "tears" help keep the eyes free of sand while females dig their nests.
E. Sea turtles on land.
1. For the most part, the only time sea turtles need to leave the sea is when females haul out to lay eggs; however, on uninhabited or sparsely-inhabited beaches, turtles have been observed basking on land.
2. Many adaptations that make sea turtles successful in the sea make them slow and vulnerable on land.
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A. Social behavior.
1. Sea turtles are not generally considered social animals; however, some species do congregate offshore.
2. Sea turtles do gather together to mate. Members of some species travel together to nesting grounds.
3. After hatchlings reach the water they generally remain solitary until they mate.
B. Individual behavior.
Little is known about the individual behavior of sea turtle species.
1. Green sea turtles are considered solitary, but occasionally from feeding aggregations in shallow waters abundant in sea grass or algae.
2. In the ocean, flat back turtles may spend hours at the surface floating, apparently asleep or basking in the sun. Frequently, seabirds perch on the backs of the flat backs.
3. Hawksbill turtles spend some time resting or sleeping wedged into coral or rock ledges.
4. Olive ridleys have been observed basking on beaches, and it is not unusual to see thousands of olive ridleys floating in front of their nesting beaches.
5. Leatherback turtles tend to dive in a cycle that follows the daily rising and sinking of the dense layer of plankton and jellyfish. The turtles probably feed in the upper layers of water at night. As dawn approaches, their dives become deeper as the plankton and jellyfish retreat to deeper water, away form the light of day. The turtles bask at the surface at midday when the layer sinks beyond their typical diving range. As dusk approaches, the turtles' dives become shallower as the layer rises.
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VII Diet and Eating Habits
A. Food preferences and resources.
Diet varies with species. Sea turtles may be carnivorous (meat eating), herbivorous (plant eating), or omnivorous (eating both meat and plants). The jaw structure of many species indicates their diet.
1. Green and black sea turtles have finely serrated jaws adapted for a vegetarian diet of sea grasses and algae. In adulthood, they are the only herbivorous sea turtles, but in an aquarium environment all sea turtle species can be maintained on a carnivorous diet.
2. Loggerheads' and ridleys' jaws are adapted for crushing and grinding. Their diet consists primarily of crabs, mollusks, shrimps, jellyfish, and vegetation.
3. A hawksbill has a narrow head with jaws meeting at an acute angle, adapted for getting food from crevices in coral reefs. They eat sponges, tunicates, shrimps, and squids.
4. Leatherbacks have delicate scissor like jaws that would be damaged by anything other than their normal diet of jellyfish, tunicates, and other soft-bodied animals. The mouth cavity and throat are lined with papillae (spine like projections) pointed backward to help them swallow soft foods.
5. Researchers continue to study the feeding habits of flat backs. There is evidence that they are opportunistic feeders that eat seaweeds, cuttlefish, and sea cucumbers.
B. Eating habits.
Some species change eating habits as they age. For instance, green sea turtles are mainly carnivorous from hatchling until juvenile size; they then progressively shift to an herbivorous diet.
A loggerhead's jaws are adapted for crushing and grinding (left). A leatherback's delicate jaws would be damaged by anything other than soft-bodied animals (right).
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A. Sexual maturity.
Researchers are still studying sexual maturity in sea turtles.
1. Estimates of sexual maturity in sea turtles vary not only among species, but also among different populations of the same species. Maturity may range from as early as three years in hawksbills; 12 to 30 years in loggerheads; to 20 to 50 years in green sea turtles.
2. Sexual maturity often is related to carapace size. Studies have shown that hawksbills reached sexual maturity at a carapace size of 60 to 95 cm (24-37 in.); loggerheads reached maturity at a carapace size of 79 cm (31 in.); and green sea turtles reached maturity at 69 to 79 cm (27-31 in.).
3. Evidence suggests that some turtles continue to grow after reaching sexual maturity, while some stop growing after reaching maturity.
B. Mating activity.
1. For most species, courtship activity usually occurs several weeks before the nesting season.
2. Two or more males may court a single female.
3. Males have enlarged claws on their front flippers. These aid males in grasping the shells of the females during mating.
4. Fertilization is internal. Copulation takes place in the water, just offshore.
C. Nesting behavior.
1. Like other turtles, sea turtles lay eggs. They must come ashore to do so.
2. Females nest a few weeks after mating.
3. Depending on the species, sea turtle nesting follows a set pattern.
a. Females usually nest during the warmest months of the year. The exception is the leatherback turtle, which nests in fall and winter.
b. Most females return to the same nesting beach each year. Recent studies suggest that some females of some species will visit more than one nesting beach in a season.
c. Females of most species usually come ashore at night, alone, most often during high tide. A female sea turtle crawls above the high tide line and, using her front flippers, digs out a "body pit." Then using her hind flippers, she digs an egg cavity. The depth of the cavity is determined by the length of the stretched hind flipper.
d. Depending on the species, the female deposits 50 to 200 Ping Pong ball-shaped eggs into the egg cavity. The eggs are soft-shelled, and are papery to leathery in texture. They do not break when they fall into the egg cavity. The eggs are surrounded by thick, clear mucus.
e. The female covers the nest with sand using her hind flippers. Burying the eggs serves three purposes: it helps protect the eggs from surface predators; it helps keep the soft, porous shells moist, thus protecting them from drying out; and it helps the eggs maintain proper temperature. Experts can identify the species of turtle by the type of mound left by the nesting female and by her flipper tracks in the sand.
f. Females may spend two or more hours out of the water during the entire nesting process.
g. Females usually lay between one and nine clutches (groups) of eggs per season.
h. It is possible that through the storage of sperm from one or several males in the oviducts of the females, all clutches of the current nesting season may be fertilized without repeated mating.
i. Females may nest every two to three years.
4. The Kemp's ridley and olive ridley form masses called arribadas (Spanish for "arrival"). Arribadas contain thousands of egg-bearing females that come ashore at the same time to lay eggs.
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IX Hatching and Hatchlings
1. Incubation time varies with species, clutch size, and temperature and humidity in the nest.
2. The incubation time for most species is 45 to 70 days.
3. Research indicates that the sex of an embryo is determined sometime after fertilization, as the embryo develops, and may be temperature dependent. Lower nest temperatures produce more males; higher temperatures produce more females.
1. Sea turtles hatch throughout the year but mostly in summer.
2. Hatchlings use a car uncle (temporary egg tooth) to help break open the shell.
3. After hatching, the young turtles may take three to seven days to dig their way to the surface.
4. Hatchlings usually wait until night to emerge from the nest. Emerging at night reduces exposure to daytime predators. They leave the nest and head to the water in groups. Studies have shown that some nests will produce hatchlings on more than one night.
C. Reaching the ocean.
1. There are several theories as to how hatchlings find the sea.
a. Hatchlings may discriminate light intensities and head for the greater light intensity of the open horizon.
b. During the crawl to the sea, the hatchling may set an internal magnetic compass, which it uses for navigation away from the beach.
2. When a hatchling reaches the surf, it dives into a wave and rides the undertow out to sea.
a. A "swim frenzy" of continuous swimming takes place for about 24 to 48 hours after the hatchling enters the water.
b. This frantic activity gets the young turtle into deeper water, where it is less vulnerable to predators.
c. There have been reports of swimming hatchlings diving straight down when birds and even airplanes appear overhead. This diving behavior may be a behavioral adaptation for avoiding predation by birds.
D. The first year.
1. During the first year, many species of sea turtles are rarely seen. This first year is known as the "lost year."
2. Researchers generally agree that most hatchlings spend their first few years living an oceanic existence before appearing in coastal areas. Although the migratory patterns of the young turtles during the first year has long been a puzzle, most researchers believe that they ride prevailing surface currents, situating themselves in floating seaweed where they are camouflaged and where they can find food.
3. Research suggests that flat back hatchlings do not go through an oceanic phase. Evidence shows that they young turtles remain inshore following the initial swim frenzy. Most remain within 15 km (9.3 miles) of land.
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X Longevity and Causes of Death
Scientists are still researching sea turtle longevity. Once sea turtles reach sexual maturity, they may have an estimated reproductive life of about 30 years. Given that some species reach maturity at 50 years, an 80-year lifespan is feasible.
Currently there is not an adequate method of aging sea turtles. The most accepted method, aside from observing a turtle from the time it hatches, is to study growth rings of the scales on the carapace and plastron. Scientists count the rings and use a mathematical formula to estimate a turtle's age.
C. Natural predators.
1. Adult sea turtles have few predators, mostly large sharks. Tiger sharks, in particular, are known for eating sea turtles. Killer whales have been known to prey on leatherback turtles.
2. Fishes, dogs, seabirds, raccoons, ghost crabs, and other predators prey on eggs and hatchlings. Most than 90% of hatchlings are eaten by these predators.
3. Flat back turtle nests are susceptible to predation by monitor lizards, dingoes, and introduced foxes.
Green sea turtles are black sea turtles may develop lobed tumor like growths (fiborpapillomas) on the skin. These growths can result in reduced vision, obstruction of normal swimming and feeding, and increased susceptibility to secondary parasitism and infection.
E. Human impact.
1. Nesting areas are becoming scarce due to beach development and disturbances. Kemp's ridleys only nest on one beach in the entire world: on a remote beach in Mexico near the village of Rancho Nuevo (about 161 km, or 100 miles, south of the Texas border). In 1947, scientists witnessed an arribada of more than 40,000 Kemp's ridley turtles in one day. In the 1960s, numbers were reduced to less than 5,000 turtles. In 1973, the largest arribada contained only 200 individuals.
2. Although the population of olive ridley sea turtles is the most abundant in the world, their major nesting beach at Gahirmatha in Orissa, India is in jeopardy. The Government of India is planning to develop a major fishing port and processing plant 10 km (6.2 miles) from the critical nesting beach. More sea turtles nest on this beach than on any other beach in the world.
3. Nesting females and hatchlings are disturbed by the presence of trash on nesting beaches. If trash impedes its crawl up the beach, a female returns to the sea instead of nesting.
4. The noise and activity of people on the beach also may cause females to return to the sea instead of nesting.
5. Some sea turtles die when they ingest trash. Leatherbacks are especially susceptible to ingesting plastic, mistaking it for jellyfish.
6. Thousands of sea turtles drown in shrimp nets each year. Sea turtles forage in waters where commercial shrimpers trawl. In 1947, 5,000 U.S. shrimping trawlers worked in the Gulf of Mexico. That number increased to 15,000 full-time and 40,000 part-time trawlers by 1989.
7. Artificial lighting on beaches may misrepresent the time of day to turtles attempting to nest. Most turtles are noctural nesters, and to a turtle that has not yet come ashore to nest, a brightly lighted beach may signify daylight and inhibit nesting.
8. Hatchlings can become disoriented by city and street lights when trying to find the surf. Many young turtles actually head away from the ocean and toward parking lots. These animals may be eaten by predators or crushed by cars. Some die from exposure.
9. Some people illegally collect turtle eggs for food and for their alleged aphrodisiac effect.
10. Sea turtles are hunted (illegally in this country and in some cases legally elsewhere) for their meat and shells, which are used to make combs, eyeglass frames, aphrodisiacs, and curious. The fat of green sea turtles, boiled with cartilage called 'calipee', made a popular soup, which led to the decline in green sea turtle population numbers.
11. Deforestation may indirectly threaten sea turtle nests. Costa Rica has one of the highest deforestation rates in the world. Some researchers fear that without the forest to draw up ground water, the water table will rise beneath the beaches and drown nests.
12. Propeller and collision injuries from boats are not uncommon. These types of injuries are more frequent in areas with a high level of recreational boating, such as South Florida, the Florida Keys, and the United States Virgin Islands.
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A. Legal protection for sea turtles.
1. All eight species of sea turtles are listed as threatened or endangered on the U.S. Endangered and Threatened Wildlife and Plants List. It is illegal to harm, or in any way interfere with, a sea turtle or its eggs.
2. The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) is an international treaty developed in 1973 to regulate trade in certain wildlife species. CITES protects all species of sea turtles. The U.S. and 115 other countries have banned the import or export of sea turtle products.
B. Turtle Excluder Device.
1. At a cost of millions of dollars, the National Marine Fisheries Service developed the Turtle Excluder Device (TED).
2. The TED is a small, metal grid trapdoor inside a trawling net that allows shrimp to pass to the back while the turtles escape to safety before becoming entrapped or entangled.
3. Since 1989, federal law requires that this device be installed on the nets of all U.S. fishing trawlers working in areas populated by sea turtles.
C. Protecting nests.
1. Nests can be protected from predators by placing screens over them. Eggs lay too close to the water or in erosion zones can be relocated to safer areas.
2. In a bold conservation program, the townspeople of a small Costa Rican village are allowed to gather eggs lay during the first two nights of each olive ridley arribada. Scientists have calculated that a controlled harvest would leave enough protected eggs to rejuvenate the population (in one nesting season, 20 to 30 million olive ridley eggs may be laid in this beach village) while allowing villagers to maintain a livelihood. The program has the potential to stop poachers of other eggs on other beaches by keeping the prices of the "legal" eggs too low for poachers to compete.
Although eliminating beach lighting would be the most effective way to reduce disorientation of hatchlings, studies have shown that low pressure sodium vapor lights have a lesser effect on loggerhead and green sea turtle hatchlings. Many beach communities have encouraged the use of these lights.
E. Wildlife refuges.
1. Legislation is underway to allocate government funding for the Archie Carr National Wildlife Refuge on the east coast of Florida, between Melbourne Beach and Vero Beach. Full protection of the refuge would cost a total of $90 million dollars, of which $50 million would come from state and local sources. As of 1994, federal funding has reached $7 million.
a. This 33-km (20.5 mile) section of beach is the most important nesting site for loggerheads in the Western Hemisphere.
b. The refuge is the most important nesting beach in the United States for the green sea turtle.
c. The refuge also is considered prime real estate for commercial development, making government funding essential to its preservation.
2. The governments of Nicaragua and Costa Rica have established, and are striving to expand, national parks and biological reserves where sea turtles forage and nest. Tortuguero, Costa Rica maintains the largest green sea turtle rookery in the Caribbean. Local economics is no longer based on turtle harvests, but on tourism. More than 15,000 visitors are expected each year.
F. Managing sex ratios.
Most conservationists believe that abundant nesting females are desirable to rejuvenate sea turtle populations. Researchers with Reproductive Sciences, Inc. and Reptile Conservation International have developed, and are patenting, a technique of applying an estrogen solution onto eggs to produce a higher number of females under normal incubation.
G. In zoological environments.
1. Having sea turtles at marine zoological parks provides an opportunity for the public to learn, up-close, about these animals and how human activities may impact their survival.
2. In the protected environment of a marine zoological park, scientists can examine aspects of sea turtle biology that are difficult or impossible to study in the wild.
3. Sea World of Florida treats numerous green and loggerhead sea turtles each year.
a. Sea turtles often are brought in after a cold weather snap. Low water temperatures cause a sea turtle's metabolism to slow - the hypothermic turtles become sluggish and are unable to feed. Marine patrol officers may find the turtles floating at the surface of the water in a semi-dormant state.
b. In December 1989, 95 hypothermic green sea turtles were rescued from Florida's Merritt Island. These turtles were housed in recovery pools at Sea World of Florida for about 10 weeks. Once the weather warmed up, the turtles were released in the same area that they were rescued.
c. Sea World has rescued other sea turtles with injuries resulting from entanglement, motorboat collisions, ocean dredging, or ingestion of non-food items.
4. Data gathered through the Sea World Animal Rescue and Rehabilitation Program and similar programs can help scientists more accurately assess and recommend sea turtle population management programs in the wild.
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