The endangered green sea turtle (Chelonia mydas) continues to be harvested for its meat by illegal poachers or by harvesters in countries where the practice is legal. The “green” in green turtle refers to the coloration of its body fat. Photo (cropped to fit): R.P. van Dam, NOAA Fisheries.
The fossil record shows that turtles appeared before dinosaurs, during the Triassic period (approximately 251-199 million years ago).1 They survived in the heyday of the dinosaur—the Jurassic period—with the first sea turtles appearing late in this period (199-145 million years ago). These sea turtles likely evolved from terrestrial or marsh-living Triassic turtle species.1 They had adapted to aquatic life by developing streamlined shells and longer, paddle-like, or webbed limbs so they could propel themselves through water. They survived the largest mass extinction, known as the K-T extinction, which killed off all ruling reptiles, except the crocodile, in the late Cretaceous period. Two families of sea turtle—both established during the Cretaceous period (145-65 million years ago)—survive today: Cheloniidae and Dermochelyidae.
Sea turtle species
Modern sea turtles are very long-lived animals. Due to their highly migratory nature, these animals are distributed globally throughout tropical to temperate marine zones—including estuarine waters. Sea turtles live in geographically diverse habitats during their various life stages; habitats vary by species, age, and even season.
Family Cheloniidae includes all species of modern sea turtle with plates, or “scutes,” covering bony shells:
- Green sea turtles (Chelonia mydas; globally distributed), including the black turtle (Chelonia mydas agassizii; found mostly in the eastern Pacific), which is not recognized as a separate species;
- Loggerheads (Caretta caretta; globally distributed);
- Hawksbills (Eretmochelys imbricata; globally distributed);
- Kemp’s ridley (Lepidochelys kempii; found in the Atlantic Ocean and Gulf of Mexico);
- Olive ridley (Lepidochelys olivacea; found mainly in the Pacific Ocean with rare sightings in the Atlantic Ocean); and
- Flatback (Natator depressus; mostly confined to Australian waters).
Family Dermochelyidae consists of only one species: Leatherback sea turtles (Dermochelys coriacea), which are found globally. Leatherbacks are known for their “leathery” skin, large body, and small bones making up the carapace (shell), and an ability to regulate their body temperature, which helps them survive in cooler waters better than the Cheloniidae species.
Life cycle and habitats
All sea turtles share the same basic life cycle that is dependent on both land and sea. Female turtles lay their eggs on nesting beaches. Hatchlings leave their nests (approximately 45-70 days after the eggs are laid) and enter the water where they will remain for the vast majority of their life. Scientists have developed a generalized model to describe sea turtle life stages based on habitat2:
The loggerhead (Caretta caretta) is found in the oceans throughout the world. Juveniles swim with their forelimbs pressed to their side and kick with their hind limbs. By the time they are one year old, they swim by alternating their front and back limbs. Photo: Smithsonian National Zoological Park, D.C.
Early oceanic juvenile nursery habitat: This encompasses the time span from when hatchlings leave their natal beaches up to more than a decade after their birth. Scientists know the least about these turtles—their oceanic lifestyles make it difficult for scientists to access and study them at this stage. The little we know comes from regional in-water observations, genetic marker data, and laboratory data. The studies suggest that some species, like Atlantic loggerheads, spend two or more years in the open ocean post-hatching, swept up by large oceanographic current systems like the mid-Atlantic Gyre or undertake long, transoceanic migrations.3,4,5,6
Later juvenile neritic developmental habitat: Anywhere from two years later to over a decade after hatching, many larger juveniles return to coastal neritic regions (roughly from the shoreline out to the edge of the continental shelf), where they feed on benthic, or bottom-dwelling organisms.7,2 They live in this habitat until adulthood. Recent data suggest that some of the larger juveniles may return to an oceanic lifestyle for extended periods.8,9
Adult foraging habitat: Depending on the species, it may take upwards of 20-30 years for a turtle to reach maturity.10 Once mature, sea turtles move into adult foraging habitats. Some adults migrate seasonally between temperate summer and winter habitats, while others may remain in one region year-round.11,12
Adult internesting and/or breeding habitat: Turtles migrate to nesting beaches approximately every one to three-plus years, where they mate offshore. Females emerge on beaches when it is time to lay their eggs. One female may lay eggs in several nests during a reproductive season, traveling to nearby internesting habitats between laying. Once the last nest of the season is laid, females leave and return to their adult foraging habitats.11,13,14 Very little is known about the movements and habitat use of adult male sea turtles since they do not leave the ocean during the nesting process.
Humans contribute to population crisis
Humans have long exploited sea turtles. In the Atlantic Ocean, sea turtles showed up on the menu in European records during the mid 1400s. It is likely that humans ate them well before that since prior to refrigeration, there were few exportable fresh meats. Sea turtles could be kept alive on deck for long periods; therefore, turtles—particularly green turtles—were used as a meat source by early European explorers in the mid to late 1400s.15
In the early 1600s, Bermuda became one of the first commercial sea turtle fisheries in the Atlantic.15,16 By 1620, however, the Bermuda Assembly passed legislation for sea turtle protection due to heavy fishing of the delicacy.17 Within 150 years, green turtles were locally exterminated.16 Over the next 400 years, turtle fisheries in the Bahamas, Ascension Island, Florida, the Cayman Islands, Cuba, and elsewhere in the Caribbean and Central America followed similar patterns of localized over-harvest.15,16
Aside from meat, turtles have also been used for:
- oil: used to worm-proof boat bottoms and soften leather (loggerhead);
- eggs: used in cooking and as aphrodisiacs;
- arts and crafts: hawksbill shells were prized for jewelry and decorative objects.
This long history of sea turtle exploitation laid the foundation for declines among many populations. All species of sea turtles found within the United States and its territories are federally protected by the Endangered Species Act (ESA) of 1973:18
- Green turtles (excluding the endangered Florida green population), olive ridleys (excluding the endangered Mexican Pacific population), and loggerhead sea turtles are considered threatened.
- The remaining leatherback, Kemp’s ridley, and hawksbill species found in U.S. waters are listed as endangered by the ESA.
- The North Pacific and Northwest Atlantic segments of the U.S. loggerhead population are currently being examined to determine if they should be reclassified as endangered.19
The ESA states that no part or product of a sea turtle may be taken, imported, exported, transported, sold, or possessed within the United States, its territories, and seas. Sea turtle nesting beaches and foraging grounds are also protected. The International Union for the Conservation of Nature’s (IUCN) Red List documents all species of sea turtle to be globally endangered or critically endangered.20
Top five global hazards
The IUCN’s Marine Turtle Specialist Group identified the top five global hazards to sea turtles:21
1. Fisheries impacts In waters where sea turtle laws and regulations prevent the direct harvest of sea turtles—by either commercial or recreational fishing—they are still captured accidentally, or incidentally in commercial fishing gear. While a particular fishery may not directly target sea turtle species, sea turtles may come across fishing gear, resulting in entanglement, prolonged submersion, and/or death by drowning or severe injury. In the high seas, it is difficult to monitor offshore fisheries (e.g., offshore or pelagic longline fisheries), or to enforce the laws and regulations protecting sea turtles. High levels of annual sea turtle mortality occur throughout the globe; commercial fishing is considered among the primary sources of sea turtle mortality.22,23 Sometimes, the turtle’s natural behavior and habitat preference may contribute to this problem.24
2. Direct takes/harvests While less common now than in past decades or centuries, some countries still allow the direct take (or harvest) of sea turtles from territorial waters and beaches. Turtles are harvested on the nesting beach and from foraging and breeding grounds for meat (particularly the green turtle) or for their shells (hawksbill); eggs are taken from nests for consumption. Traditional methods of in-water turtle capture include gill netting, harpooning, and seine nets. The Convention on International Trade of Endangered Species prohibits the international trade of threatened or endangered species.25 While this treaty helps reduce the trade of turtle meat, eggs, and shells, it requires only voluntary participation by signatory countries.
The leatherback (Dermochelys coriacea) is the largest sea turtle and the only living species in the genus Dermochelys. It can be identified easily by its lack of a bony shell, which is why females choose beaches with soft sand for nesting. The hatchlings are confused by artificial lighting and may not head for the ocean. Photo: marinebio.org.
3. Coastal development Sea turtles are known to have strong attachments to nesting and foraging sites.9,13,26,27 Female sea turtles are thought to return to beaches where they were born to nest as adults and will often return to the same beach to nest both within a nesting season and interannually.28,29,30 This repeated fidelity to specific locations may put these turtles at risk if their foraging or nesting grounds are threatened or altered. Examples include:
- fishing activities
- channel or shipping lane dredging/maintenance
- beachfront development
- coastal armoring
- invasive plant species
- beach nourishment
- beach erosion (resulting in nest exposure, tidal or storm over-wash of nests); and
- general public use of beaches (e.g., beach driving).
Beachfront lighting, an artifact of coastal development, and considered light pollution, is another source of potential mortality for sea turtles. When hatchlings emerge from their nests, one cue that helps them orient seaward is light reflecting off the sea’s surface; bright lights associated with developed beachfronts may disorient hatchlings and cause them to crawl towards land instead of the ocean.31,32,33,34
4. Pollution and pathogens
The presence of discarded plastics, tar, and other trash in coastal and offshore habitats impacts sea turtles at all stages of their lives. Turtles may mistakenly ingest plastics (e.g., balloons or plastic bags) or petroleum byproducts (tar) that can cause illness and/or susceptibility to pathogens, injury, and even death. Early nursery habitats—such as floating Sargassum algae mats for young oceanic loggerhead juveniles—are affected by a variety of pollutants. Studies have found a large percentage of these young Florida loggerheads had digested tar.35 Additional pollutant impacts include:
- bio-accumulated chemicals (e.g., PCB’s)
- bio-accumulated mercury
- styrofoam ingestion; and
- habitat alteration from agricultural run-off or sewage.
5. Global warming
An emerging, long-term threat to sea turtles is global warming. One of the primary effects of global warming on sea turtle populations includes habitat loss (nesting and foraging). Coral reef systems provide developmental, foraging, and an internesting habitat for many species of sea turtles. With rising sea temperatures and ocean acidity, these habitats are now at risk. Sea turtle nests, eggs, and embryonic development are very susceptible to fresh- and saltwater inundation and beach erosion resulting from excessive rainfall or storm effects.36 With the possibility of sea level rise, nesting beach habitats may slowly disappear or experience increased impacts from storm damage. During embryonic development, the sex of a turtle is determined by the temperature at which the embryo incubates. Global changes in temperatures may influence changes in sea turtle sex ratios.37,38,39 Changes in sea temperatures may also result in a redistribution of sea turtle prey, and a potential pole-wards redistribution of sea turtles into warming waters that, in recent history, have been too cold to support sea turtles.39
Management and conservation
Sea turtle conservation and management is a global issue. Turtles do not acknowledge human boundaries. They have complex life histories that span many decades, habitats, and kilometers. All sea turtle species and age classes travel very long distances annually, often entering many different international territories. Slow growth rates, combined with late maturity, require that these animals must survive from one to three decades before they are able to reproduce and contribute to their population.
To put this into perspective, some species take almost twice as long as humans to reach reproductive maturity. Due to their geographically diverse life stages, there may be a time lag between when a population hit occurs, and when a decline is observed. If a mortality event occurs during the early pelagic of oceanic juvenile life stages, for example, decades may go by before the effects are observed (e.g., fewer new females emerging on nesting beaches). Sea turtles, therefore, are extremely vulnerable to the global hazards listed above. Sea turtle populations may take decades, or generations, to recover from such impacts.
Due to sea turtles’ migratory behavior and oceanic life stages, we have significant gaps in our understanding of these animals. We have only a snapshot of their overall life histories, and to manage these animals effectively, the status and condition of each stock must be understood at each life history stage.40 Existing population models rely on data collected on nesting beaches, which skews the findings towards nesting females and the earliest of life stages — hatchlings. Gaps in data make it difficult to assess conservation and management efforts. Legal initiatives are highly dependent on advancements in scientific knowledge and require the use of “best available information,” and this information is very limited, which often results in a patchwork-quilt approach to sea turtle management, where only specific habitats or stages are or can be protected.
While recent conservation efforts have resulted in increasing some populations (e.g., Kemp’s ridley, Atlantic green, and leatherback), recent stock assessments for some populations are not as optimistic—particularly for Pacific leatherbacks and Atlantic loggerheads.19,41 It is possible to help protect sea turtle species through legislation and regulation; nonetheless, in order to be effective, laws and regulatory policies depend on sound science and knowledge of the species. Management needs to occur at local, state, federal, and international levels. The gaps in our understanding of these animals need to be filled, which requires political will and long-term research and funding commitments over multiple sea turtle generations.
What can citizens do to help conservation efforts?
The public can do many things to help mitigate the hazards faced by sea turtles during all stages of their life histories. It does not matter where you live—on a coast or hundreds of miles inland—there are small steps everyone can take to contribute to the future survival of these species.
- If you accidentally capture a sea turtle while recreationally fishing (hook or entanglement), or encounter a turtle in the wild that is tangled in commercial fishing gear (netting, monofilament fishing line, or fishing hooks), the turtle may need veterinary care—especially if the turtle has ingested the line or hook and/or has other visible injuries. If possible, report the incident to your local sea turtle stranding network for further instructions.
- Be informed—when you buy seafood at the store or order it at a restaurant, find out where it comes from. Ask questions about where and how it was harvested.
Refrain from buying jewelry and other crafts made of hawksbill shells. Photo: Caroline Rogers, USGS.
- Do not purchase products made from sea turtle parts when traveling or living in countries that still allow sea turtle harvest.
- In countries where sea turtle harvest is prohibited, inform local authorities of any illegal activities (egg poaching and harvesting of turtles).
- Reduce beachfront light pollution—encourage beachfront property owners to install “turtle-friendly” lighting or to turn off their lights in areas where sea turtles nest.
- Avoid driving vehicles on nesting beaches during the nesting and hatching seasons.
- If you encounter a sea turtle in the wild, do not touch or disturb it. If you are on a beach at night, do not shine lights on or near the turtle (this includes camera flashes).
Pollution and plastics
- Bring your own reusable bags when shopping and avoid using plastic bags.
- Do not release balloons—they travel long distances and are known to be ingested by sea turtles.
- Participate in or organize regular coastal clean-ups—even in areas where sea turtles are not known to occur. Trash will travel!
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