Sea Turtles: Ambassadors of the Sea

Sea turtles are found in all of the world’s oceans with the exception of the Arctic Ocean, and many migrate thousands of kilometers as part of their life cycle. Sea turtles are potentially a Keystone species (Website 1) and “play an important role in coastal and marine habitats by contributing to the health and maintenance of coral reefs, seagrass meadows, estuaries, and sandy beaches” (Eckert et al., eds., 1999). Despite their critical role, due to increased commercialization of turtle products, habitat loss, and other anthropogenic causes, almost all species of sea turtles today are listed as “Critically Endangered,” “Endangered,” or “Vulnerable” (Eckert et al., eds., 1999).

Green turtle in Hawaii

Photo source: Wikimedia Commons

A World in Jeopardy—the importance of a plan for conservation

"Soon a millennium will end. With it will pass four billion years of evolutionary exuberance. Yes, some species will survive, particularly the smaller, tenacious ones living in places far too dry and cold for us to farm or graze. Yet we must face the fact that the Cenozoic, the Age of Mammals which has been in retreat since the catastrophic extinctions of the late Pleistocene is over, and that the Anthropozoic or Catastrophozoic has begun." --Michael Soulè (1996)

Defining Conservation Biology—what is it and how does it work

Conservation biology is an interdisciplinary science, integrating the biological and physical sciences, environmental law and policy, economics, environmental ethics, ecology, climatology, social sciences, and geography (textbook).

Sea Turtle Family Tree—evolution of turtles and sea turtles

Over the last 310 million years, 16 Orders of reptiles evolved, only four of which are alive today. Turtles, terrapins, and sea turtles make up one of these orders, Testudinata (also called Chelonia), which is comprised of two sub-orders, Cryptodira and Pleurodira. The Pleurodira are also known as side-necked turtles, for the way in which their heads retract into their shells in a side-ways manner. The suborder Pleurodires, also the straight-necked turtles, is composed of 220 species of extant turtles, only seven of which are marine. These seven species belong to two distinct families, Dermochelyidae and Cheloniidae. The family Dermochelyidae consists of one species, the soft-shelled, leatherback sea turtle, Dermochelys coriacea. Six species of hard-shelled sea turtles make up the family Cheloniidae, including: Chelonia mydas, the green sea turtle; Natator depressus, the flat-backed sea turtle; Eretmochelys imbricata, the hawksbill sea turtle; Lepidochelys kempii, Kemp’s Ridley sea turtle; Lepidochelys olivacea, Olive Ridley sea turtle; and Carreta carreta, the loggerhead sea turtle.

Sea Turtle Anatomy 

In all turtles, the upper shell is called the carapace, and the lower shell is the plastron. The carapace is generally thicker and less flexible than the plastron. They are connected on the sides by bony structures called bridges. The inner shell is made up of bones, some which are portions of ribs or backbone. Because of this, a turtle cannot crawl out of its shell, and to try to remove one from its shell would mean death for the turtle. Thick, horny scales, called scutes, cover the outer layer of the shell. The scutes, made of the protein keratin, add strength to the shell. The leatherback turtle, unlike the hard-shelled sea turtles, has a soft, leathery shell consisting of oil-saturated connective tissue, which overlays interlocking dermal bones. In all turtles, where the skin not covered by shell, it is composed of smaller scales such as those found in snakes and lizards. Turtles do shed their skin, but not all at once like snakes. Instead, their skin sheds continuously in small increments. Scutes do not shed; they accumulate overtime and become thicker.

The shape of a turtle’s shell can often be used to define their lifestyle. Land tortoises have deeply-domed shells that help protect them from predators. Sea turtles, on the other hand, have flattened, streamlined shells that make them highly efficient in the marine environment. Their feet have evolved into flippers. Front flippers are used for creating thrust by a series of up and down motions. The back flippers act as rudders, steering the turtle through the water. Due to swimming ability, large size, and tough shells, most adult sea turtles have few predators other than larger sharks and humans. On land however, they are slow and defenseless.

An Introduction to Sea Turtles

Flat-backed sea turtle (Natator depressus)

The flat-backed sea turtle is named for its flattened carapace, which is usually olive-gray in color, with upturned edges. The plastron is generally pale yellow. There is a single pair of prefrontal scales in front of the eyes. Average carapace length is approximately 99cm, and average weight is 90kg. 1. There are four lateral scutes on the carapace., and flippers have one claw. Shells are thin and easily damaged. 2. Flat-backs eat a diet high in protein, feeding on squid, sea cucumbers, soft corals, and mollusks.

Flat-backs are indigenous to the coastal waters of Western, Northern, and Eastern Australia, and also the Gulf of Papua, New Guinea. Unlike most other species of sea turtle, flat-backs often live in turbid waters near-shore. 1. Nesting takes place in November and December along the Northern coast of Australia 1., and the female may nest up to four times per season, with an average clutch size of 50 eggs.2. The eggs incubate for approximately 55 days 2., and when the hatchlings emerge, they are relatively larger than hatchling of other sea turtle species. 1. Predators to baby sea turtles are rats, monitors, herons, sea eagles, dingos, and foxes. Salt water crocodiles are also dangerous to all flat-backs. 1.

In 1994, the flat-backed sea turtle was listed as Vulnerable on the IUCN red List. Like all other sea turtles, they are protected under Appendix I and II by CITES. *

Hawksbill sea turtle (Eretmochelys imbricata)

The hawksbill is a small to medium-sized sea turtle named for its elongated head, which narrows into a pointed mouth resembling a parrot’s beak. This beak shape allows the hawksbill access to sponges, its favorite food, which it finds in crevices and holes of coral reefs.3.Typical weight for this species is between 45 and 68 km, and carapace length averages 63 to 90 cm.3. Carapace color can range from dark to golden brown, with tortoiseshell designs in orange, red, and black. The plastron is generally yellow. The rear-edge of the carapace is serrated with over-lapping scutes, although older adults may not exhibit the serration. 3. There are two pairs of prefrontal scales on top of the head, and flippers usually have two claws.

The hawksbill can be found in the Atlantic, Pacific, and Indian Ocean, and is widely distributed in the Caribbean Sea and the West Atlantic. They are regularly sighted in Southern Florida, the Gulf of Mexico, and along the coast of Central America, South to Brazil. They are very common in Puerto Rico, and the Virgin Islands, but are not found in the Mediterranean. The sightings of hawksbills around Texas and Florida are usually juveniles, which most likely have migrated from nesting beaches in Mexico. 3. Females usually travel to nesting beaches every two years, where they may nest between three and five times per season. Average clutch size is approximately 130 eggs.

Hawksbills are highly associated with coral reefs, and some are known to return to the same resting spot—usually ledges and caves of coral reefs—every night. Aside from coral reefs, they may also inhabit mangrove forests in marine bays. 3.

Kemp’s Ridley sea turtle (Lepidochelys kempii)

Averaging 68-82 cm, and weighing between 33-45 kg, the Kemp’s Ridley is the smallest sea turtle and the most endangered sea turtle in the world. 4. Adults have a heart-shaped body, and are olive to gray-green, with creamy-white skin. The plastron is cream to tan, and the darkly-spotted head and flippers stand out against the paler underside. These sea turtles eat crabs, and the occasional shrimp and fish. 5.

Unlike other species of sea turtles who nest primarily at night, Kemp’s Ridley regularly nest in the daytime, with females building between two and three nests per season. 5. Nesting season usually begins in early April, and ends by the end of July, or early August. Large aggregations of nesting females are called arribazones in Spanish, but the numbers of nesting females have drastically decreased in recent years. 4. Incubation lasts between 48-62 days, at which point thousands of hatchlings will make their way from the nesting beaches into the ocean. For almost every 125,000 hatchlings, only about 1% will survive to sexual maturity, which is generally reached at 10-15 years of age. The age of sexual maturity in males is unknown. 4.

Olive Ridley sea turtle (Lepidochelys olivacea)

This small sea turtle, generally weighing less than 45 kg, is Endangered in Mexico, and listed as Threatened elsewhere. 6. They are perhaps the most abundant sea turtle in the world.6. Their overall color is olive-green, explaining both their common and Latin names. They have two-pairs of prefrontal scales, and the upper shell has 5-9 costal scutes, and 7 vertebral scutes. The latter charachteristics can be used to distinguish this species from Kemp’s Ridgley, which has 5 costal and 5 vertebral scutes.  6. Their primary foods are shrimp, rock-lobsters, tunicates, mollusks, crabs, and jellyfish. 7. They have also been known to eat algae in some parts of the world. 7.

The age at which this species reaches sexual maturity is unknown, but could be similar to Kemp’s Ridley, where females reach sexual maturity between 10-15 years. Like the Kemp’s Ridgley, large aggregations of nesting females are called arribazones, and they may converge after climatic events, or during certain phases of the moon and tide.7. This species is known to nest between 1-3 times per season, lying an average clutch size of 110 eggs. After between 52-58 days of incubation, the baby turtles hatch.

Olive Ridley sea turtles are found in tropical and subtropical coastal bays and estuaries.6. They are found in all oceans, with the exception of the Arctic; from the Atlantic coast of West Africa, west to South America. In the Pacific, they can be found from Southern California to Northern Chile. Arribazones occur on the Pacific Coast of Costa Rica, and Pacific Mexico at La Escobilla, Oaxaca. 6.

Loggerhead sea turtle (Caretta caretta)

Loggerheads are named for their large heads, which have powerful jaws—great for eating their favorite foods of conchs and whelks. 8. The average carapace length is around 92 cm, and average weight is 113 kg. The carapace is slightly heart-shaped, and reddish-brown in adults and sub-adults. The plastron is generally pale yellow. The neck and flippers are brown or reddish on the surface, and pale yellow on the sides and bottom. 8.

Loggerheads reach sexual maturity at around 35 years of age. Mating takes place from late March through early June in the southeastern United States, and females begin nesting late April through early September. From three to five nests are laid per season, with eggs hatching after about two months of incubation. Hatchlings are light to dark brown and gray dorsally, with yellowish to tan plastrons.

These turtles are found throughout temperate and tropical regions of the Atlantic, Pacific, and Indian Oceans, and they are considered the most abundant species found in U.S. coastal waters.

Green Sea Turtles (Chelonia mydas)

Some scientist seperate Chelonia mydas into two different species--Chelonia mydas mydas, the green sea turtle, and Chelonia mydas agassizzii, the black sea turtle. More often, these turtles are classified as subspecies of two different populations. Chelonia mydas mydas is found in the Atlantic and Caribbean, and Chelonia mydas agassizzii is found in the Eastern Pacific. For the purposes of this article, they will be considered one species, and referred to as the green sea turtle.

In general, green sea turtles are the largest of the hard-shelled sea turtles, with adults ranging from 1.3-1.5 meters, and weighing approximately 113-204 kg. The turtles found in the Eastern Pacific are smaller, with adult carapace length averageing approximately 100 cm, and weighing around 100 kg. Carapace color can be green, black, or brown, or any combination of these colors. The plastron is yellowish or white. The green sea turtle is not named for the color of its shell, but for the color of its fat, which is green due to its adult diet of algae. Hatchlings and juveniles may eat crabs, crayfish, comb jellies, and jellyfish, but adults feed primarily on algae. This herbaceous diet does not require the strong beak of the hawksbill, and the heads of green sea turtles are round in shape.

Green sea turtles can be found in all the world's oceans where temperatures do not fall below 20 degrees Celsius. They are considered Threatened or Endangered throughout their range, although green sea turtles found in the Mediterranean are critically endangered. An important nesting site for the Atlantic population is in Tortuguero, Costa Rica. For the Indo-Pacific subpopulation, a few well-known nesting grounds occur in Mexico, the Hawaiian Islands, the South Pacific, and the Northern Coast of Australia. For the Mediterranean population, Cyprus and Southeastern Turkey are the primary nesting sites.

Leatherback sea turtle (Dermochelys coriacea)

 This species is the largest turtle, and the largest reptile in the world. Adults can be up to 2 meters in carapace length, and weigh up to 900 kg. This is the only species in the Family Dermochelyidae, all other sea turtles belonging to the Family Cheloniidae. As its name states, this species lacks a hard shell, rather it has a leathery shell approximately 4 mm thick. Its carapace tapers to a blunt point at the back. The turtle's skin has a pink-mottled appearance, and pale white and pink spotting on top of the head. The front flippers lack claws and scales, and the back flippers are paddle-shaped. The leatherback is the most migratory, and wide-ranging of all sea turtles, and it is able to tolerate colder waters than other species. It is mainly found in pelagic environments, but may also be seen foraging in coastal waters. Its food of choice is soft-bodied prey such as jellyfish or salps, and its mouth and throat are adapted to retain this gelatinous prey having backwards-pointing spines.

Leatherbacks have nesting-grounds world-wide, but some of the largest are found on the coasts of South America and West Africa. There are also smaller colonies in the United States Caribbean, and Southeast Florida.The female may nest several times per season, and clutches of approximately 100 eggs are normal. Hatchlings emerge after 60-65 days, and have a dark body with white-striping running along the ridges on the back, and on the flippers.

 Because of their ability to tolerate colder waters, leatherbacks have been sighted as far north as the Gulf of Maine, and off Newfoundland where water temperatures are as cold as 0-15 degrees Celsius. However, juveniles smaller than 100 cm are usually only sighted in waters warmer than 26 degrees Celsius or warmer.

Sea Turtle Life History—reproduction, diet

Threats to Sea Turtles

There are many reasons for the decline of the world’s sea turtles, but most reasons are the result of  “adverse consequences of human activities” (Tisdell and Wilson, 2002). For as long as human have inhabited coastal ranges, they have been linked to sea turtles, and have greatly impacted populations through activities such as hunting turtles for meat and ornamentation, collecting eggs for consumption, using turtles for oil and aphrodisiacs, and habitat degradation. C. mydas in particular, is known for its use as an ingredient in turtle soup. Modern fishing techniques claim the lives of tens of thousands of sea turtles annually (IUCN) through the use of fishing trawls, long-line fishing, drift nets, and coastal gill nets. At one time, more than 55,000 sea turtles drowned in shrimp-nets in the southeastern United States alone (Website 4). Glow sticks used to attract billfish and tuna in long-line fishing might be what is attracting sea turtles to their deaths. Turtles may mistake the glow sticks for jellyfish, or the attraction could be an “instinctive reaction to the unnatural continuous light” (Website 14).

Construction of roads and buildings close to nesting beaches not only removes habitat, but creates artificial lighting, which causes confusion for hatchlings and nesting mothers. Recreational use of beaches compacts sand in nesting areas, and destroys eggs that have already been laid. Coastal armoring--bulkheads and riprap--and beach nourishment, which act to prevent erosion, have also been shown to significantly alter nesting habitat (Website 11). Invasive species, introduced by human such as cats, rats, and hogs, dig up turtle nests to eat the eggs.

Pollution, chemical, physical, and thermal, create a plethora of problems for sea turtles. Plastic debris can be mistaken  for food items, and while C. mydas have a primarily herbivorous diet, plastic bags and other wastes cause intestinal blockages, often resulting in death. In one study, 9 out of 12 C. mydas necropsied after death were found to have died due to plastic-related causes, and the plastic ingested consisted of not only plastic bags, but disposable razors, soda bottle tops, children’s hair barrettes, among other items (personal observation). Aside from causing internal blockages, plastic can also release toxins into the internal organs over a period of time (Website 15).  Plastic six-pack soda rings and discarded fishing line have been found to restrict growth movement in turtles and other sea-life, and eventually result in strangulation or limb amputation (Website 4).

The effects of chemical pollutants on sea turtles are just now being realized and studied. In a study by Saeki et al.(2000), high levels of arsenic were found in the liver, kidneys, and muscle of three species of sea turtle, including C. mydas. The algae the green turtles rely on for sustenance contained arsenic levels at 1,000-50,000 times the level of ambient sea water (Saeki et al., 2000). In a separate study in 2006, four species of sea turtles from the Baja, California peninsula of Mexico were found to contain Cadmium concentrations at levels higher than had ever been reported (Gardner et al., 2006). Sea turtles have been found with balls of oil and tar in their stomachs (Website 15) and it has been found that short-term exposure to crude oil may produce the death of epidermal epithelium in C. mydas (Lutcavage et al., 1995). Sonic pollution creates another problem. Seismic tests during oil exploration, the testing of weapons, and low-range frequency communications by  submarines has been shown to pose a threat to marine turtles (Frazier et al., 2007).

A particularly distressing problem, that has become a major concern within the last 30 years, is the rapid increase in the number of sea turtles found with fibropapillomatosis (FP), a disease which is characterized by “epizooitic tumors of the skin, flippers, periocular tissues, carapace, and plastron” (Aguirre and Lutz, 2004). The tumors themselves appear to be benign, but as they grow they can severely restrict swimming efficiency, affect motor skills, and diminish eyesight. The tumors may also spread into internal organs where they may become malignant. Tumors inside the mouth may inhibit the intake of food (Aguirre and Lutz, 2004). This disease was first reported in C. mydas caught in  Florida in the 1930’s (Aguirre and Lutz, 2004), but has now been found in all sea turtle species on a global scale. One survey conducted in Kaneohoe Bay, on the island of Oahu, Hawaii in 1991, indicated that as many as 92% of C. mydas were infected with the disease (Balazs and Pooley, 1991). The cause of FP is unknown, but a variety of hypotheses are being examined, and two groups of viruses have been found to be associated with the disease, the herpesvirus, and retrovirus, with herpesvirus being found in 95% of all tumors in one Florida study (Aguirre and Lutz, 2004). Predisposing factors suggested for the disease are environmental pollutants, biotoxins, changing water temperatures, infectious agents, and immunosuppression (Aguirre and Lutz, 2004).

Global warming may also impact sea turtle populations, as extreme weather changes may increase disease outbreaks, including FP, result in loss of nesting beaches, destroy coral reefs, and alter other critical habitat (Website 17). Another consequence of changing weather patterns might be an impact on sex-ratios of hatchlings, which could prove disastrous for sea turtle populations (Godfrey, 1997), due to TSD.

Sea Turtle Conservation

Out of the seven species of sea turtles, all but one are considered Endangered by the World Conservation Union (IUCN). C. mydas was listed on the IUCN Red List of Threatened Species in 2000 as Endangered. Over the last 10 years, the population has experienced a reduction of at least 80 % (Website 18) based on direct observation. In 1973, The Endangered Species Act (ESA) in the USA listed all populations of C. mydas in U.S. waters as Threatened, with the exception of breeding populations in Florida, and off the coast of Mexico, which are Endangered.

In the United States, protection of Threatened and Endangered sea turtles is a shared responsibility between the National Oceanic and Atmospheric Administration (NOAA), and the United States Fish and Wildlife Service (USFWS), with NOAA having jurisdiction over the conservation and recovery of sea turtles within the marine environment, and USFWS protecting nesting beaches. On a global scale, by 1981, the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), gave all sea turtle species an Appendix 1 status, completely banning the commercial trade of all species listed.

In the United States, the ESA has established requirements for the fishing industry to reduce the number of incidental capture of sea turtles. The use of Turtle Exclusion Devices (TEDs), trawl nets that include an escape opening for turtles, are now mandatory for most shrimp trawlers operating in the South-Eastern United States. To meet standards set by the National Marine Fisheries Service, TEDs must be proven to be at least 97% effective in reducing the number of turtles captured (Website 4). Circle hooks are also being incorporated to reduce the amount of by-catch from longline fishing. Research is on-going to establish whether these hooks prove economically viable to the fishing industry, reduce bycatch in all fishing areas, and if all circle hooks reduce bycatch numbers to the same degree (Read, 2007). Researchers are also working with fishing industries to reduce bycatch from the glow sticks used in logline fishing. One possible strategy, "is shading the light sticks to direct the light downward. Sea turtles use the top portion of the water column, while most target fish are caught as they move upward from deeper water” (Website 14).

Even with legal protection at global and local levels, sea turtles are still at risk. There are currently 172 countries participating in CITES, nevertheless Countries such as Italy persist in importing oil derived from the fat of C. mydas from the Cayman Island Turtle Farm although this importation is in violation with CITES and the European Economic Community (EEC) (Website 2). There is also limited participation in many tropical countries, and Japan receives an extensive amount of turtle shell from the Solomon Islands, Fiji, the Comoros, and the Maldives (Website 2). In Mexico, sea turtles have been protected since 1990, although turtle habitat is still in danger. It is estimated that up to 90% of nesting habitat has been destroyed to develop seaside condominiums and hotels, many which cater primarily to North Americans (Laduke, 2006).

Because of the growing concern over sea turtles, a large number of non-governmental organizations (NGOs), and grassroots groups have come together to help protect sea turtles all over the world. Popular organizations such as Defenders of Wildlife and World Wildlife Fund, have established sea turtle conservation programs. For example, Defenders of Wildlife has created their Defenders Mexico Program, which sets up conservation workshops with Mexican fisherman, officials, and outside experts to demonstrate sea-turtle-friendly fishing practices, and to demonstrate actions to take if sea turtles are accidentally captured (Website 19). Other non-profit organizations such as the Caribbean Conservation Corporation, were established with the sole purpose of sea turtle conservation. Founded in Florida in 1959, the CCC chose sea turtles as its focus “in part because these ancient creatures are among the most important indicators of the health of the world's marine and coastal ecosystems’ (Website 4). The CCC promotes public involvement in sea turtle research, recruiting volunteers to participate in research programs. In this, the CCC is not alone. Hands-on opportunities in sea turtle research and conservation are becoming more and more popular with groups such as Earthwatch, Watamu Turtle Watch, ANAI Sea Turtle Conservation Program, Proyecto Karumbe, and the Grupo Ecologico de la Costa Verde, which all offer volunteer positions or internships. These groups, among many others, also accept donations and many allow people to “adopt” a sea turtle. These funds go towards research in sea turtle conservation, provide community outreach programs, and promote sea turtle awareness.

In a more recent turn of events, ecotourism based on sea turtles is becoming more popular, especially with programs such as Brazil’s Projecto TAMAR yielding positive results (Godfrey and Drif, 2001). In the past, sea turtle conservation aimed at keeping the public off of nesting beaches, but by creating awareness and funds through the use of visitor centers, turtle-watch programs, and shops, community participation and involvement are expected to aid conservation practices (Godfrey and Drif, 2001). However, ecotourism should not be regarded as a “quick-fix” (Eckert, et al., eds., 1999).  They state, “Nesting beaches are being destroyed at unprecedented rates to accommodate the fastest growing industry in the world: tourism. Economic exploitation from the outside, where only a small part of the profits effectively reach the communities, should be avoided.” There is also growing evidence that many ecotourist programs are in fact, failing to achieve their goals, and could potentially be damaging sea turtle populations (Godfrey and Drif, 2001).

Indigenous groups, like the Seri peoples in Sonora, Mexico, have began organizations to help restore the sea turtle. (Laduke, 2006). According to Gabriel Hoffer, a Seri, “ It’s important that our traditional knowledge can help restore the turtles. They’re a very sacred animal to us” (Laduke, 2006). Taking a very different approach, Argentinian model Dorismar began a campaign to eliminate the harvest of sea turtles for use as aphrodisiacs. In ads, the scantily-clad Dorismar states in Spanish, “My man doesn’t need turtle eggs!” (Laduke, 2006). Even the beer industry has found its own way to help sea turtles. In 2004, the Portland Brewing Company launched Honu (the Hawaiian name for green sea turtles) Beer into the marketplace. For every bottle of Honu beer sold, the World Turtle Trust was chosen to receive a donation to aid in sea turtle conservation (Website 20).

To help prevent pollution, some cities such as San Francisco, in the United States have banned plastic bags. Even Tanzania’s archipelago Zanzibar has banned the use of plastic bags to help protect their fragile ecosystem. Unfortunately, these laws are hard to enforce in many countries, and in Zanzibar, whose implementation regarding environmental laws has been lax (website 21), plastic bags are still heavily used (personal observation). To help limit the use of light pollution near nesting beaches, embedded road lamps are being examined to determine whether or not the use of such lighting will reduce hatchling mortality (Bertolotti and Salmon, 2005). In their study, they concluded that the embedded lights did in fact give off less illumination than streetlights, and also confined the light to road surfaces.

Links to Sea Turtle Conservation Organizations

o        Sea Turtle Conservation Bonaire

o        Wider Caribbean Sea Turtle Conservation Network WIDECAST

o        Sea Turtle Preservation Society STPS

o        Archie Carr Center for Sea Turtle Research ACCSTR

o        Turtle Watch

o        World Turtle Trust

Sustainable Use Versus Conservation

How We Can Help

Activities for Children

References