Green sea turtle

Sea turtles: Frequently asked questions (FAQ)

What species of sea turtles are known?

The seven species of sea turtles living today are divided into two major groups, the leathery-shelled sea turtles (Dermochelidae) and the hard-shelled sea turtles (Cheloniidae). Of the first group, only one species has survived into modern times, the leatherback sea turtle (Dermochelys coriacea). The six species of hard-shelled sea turtles are the loggerhead sea turtle (Caretta caretta), the olive ridley sea turtle (Lepidochelys olivacea), the Atlantic ridley sea turtle (Lepidochelys kempii), the hawksbill sea turtle (Eretmochelys imbricata), the flatback sea turtle (Natator depressus), and the green sea turtle (Chelonia mydas).

Sometimes you can hear about an eighth species of sea turtle, the black sea turtle of the Eastern Pacific. However, this is now considered only a subspecies of the green sea turtle.

In the remote past (but not so remote in terms of geological time scales) there was a third major group of sea turtles, the Protostegidae, which were closely related to the leatherback turtles. These became extinct in the middle of the tertiary about 35 million years ago. They included the largest known sea turtle, Archelon ischyros, with a total length of up to 5 meters.

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How long have sea turtles been on earth?

Frequently, the high geological age of the sea turtles is pointed out and they are often called “dinosaurs of the seas”. Indeed, it is clear that the sea turtles represent a conservative group of animals that have changed relatively slowly in the course of the earth’s history. However, often quite different data about the exact geological age of the sea turtles can be found. To make it short, the group forming the living sea turtles probably is about 120 to 150 million years old.

The last known common ancestor of the  leatherback turtles and the Protostegidae, which is known by fossil finds, lived about 120 million years ago (early Cretaceous). Since the hard-shelled turtles forked from this lineage somewhat before, it can thus be concluded that the group forming leatherback and hard-shelled sea turtles together (the “modern sea turtles” or Panchelonioidea) is older than 120 million years, but not much older than about 150–160 million years (late Jurassic), when the last common ancestor of all modern land and water dwelling turtles and tortoises (Testudines) lived. However, the ancestry of all turtles and tortoises, from which, interestingly, aquatic species that are now long extinct have evolved several times independently throughout Earth’s history, goes back deep into the Triassic period more than 220 million years ago, along with the dawn of the dinosaurs.

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Where do sea turtles occur?

Sea turtles are found in all tropical and subtropical seas. Leatherback turtles occur even in colder waters and are observed quite frequently, e.g., off the coasts of Scotland. Most sea turtles have a global distribution within their preferred latitudes, with only the occurrences of the Kemp’s ridley turtle and the flatback turtle locally restricted to the Gulf of Mexico (Kemp’s ridley) and the northern coastal waters of Australia and southern New Guinea (flatback). Leatherback turtles and populations of loggerhead turtles are adapted to life in the high seas; most other species, however, tend to live nearshore or on the shelf, crossing the high seas only on migrations.

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How big do sea turtles grow?

The largest species of sea turtle is the leatherback turtle, with a length of up to two meters and a possible maximal weight of almost one metric ton. The span of the pectoral fins can be up to 2.7 meters. The largest hard-shelled sea turtle is the green sea turtle with a length of up to 1.2 m and a maximum weight of 225 kg.

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How old do sea turtles get?

No sea turtle has ever been tracked in the wild from birth to natural death. Therefore, their actual natural life expectancy is largely unknown. However, based on the information we have, it is believed that sea turtles can live to be 60 or more years – depending on the species. Recent research in South Carolina found that a grandmother turtle was breeding at the same time as her granddaughter turtle. Considering that loggerhead sea turtles take about 30 years to become reproductively mature, these results show that females can still live and nest at over 90 years of age.

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When does a sea turtle reach sexual maturity?

The estimated sexual maturity of sea turtles varies not only between species, but also between different populations of the same species.

Sexual maturity can range from 7 to 13 years for leatherback sea turtles, 11 to 16 years for both species of ridley turtles, 20 to 25 years for hawksbill sea turtles, 25 to 35 years for loggerhead sea turtles, and 26 to 40 years for green sea turtles. Because green sea turtles feed primarily on sea grasses and algae, they usually reach sexual maturity later than the other, more carnivorous sea turtles.

Sexual maturity is often related to carapace size. Studies have shown that hawksbill sea turtles reach sexual maturity at a carapace size of 69 to 78 cm. Loggerhead turtles reach sexual maturity at a carapace size of about 50 to 87 cm. Leatherback turtles reach sexual maturity at 145 to 160 cm. Turtles usually continue to grow after reaching sexual maturity, but at a noticeably slower rate.

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What do sea turtles eat?

  • Each species of sea turtle has a typical food spectrum:
    Australian flatback sea turtles are primarily carnivorous, feeding in shallow waters on soft bottoms.
  • Green sea turtles have a vegetarian diet and as adults prefer sea grass and algae. Green sea turtle hatchlings, however, are omnivorous and eat jellyfish, snails, crabs and shrimp.
    Hawksbill sea turtles have a bird-like beak that allows them to eat soft corals, anemones, and sea sponges.
  • Early in life, the Kemp’s ridley sea turtle is omnivorous, feeding on algae and small creatures such as crabs and snails. As adults, Atlantic bastard turtles forage on the ocean floor and feed on crustaceans, fish, mollusks, squid, and jellyfish.
  • Leatherback turtles feed primarily on jellyfish.
  • Loggerhead turtles feed primarily on hard-shelled organisms such as lobsters, crustaceans, and fish.
  • Olive ridley sea turtles are omnivorous, feeding mainly on jellyfish, snails, crabs and shrimp, but also on algae and kelp.

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How can I tell the difference between males and females in sea turtles?

The males have a much longer and stronger tail than the females. Furthermore, claws on the front fins are elongated in males, which helps them to cling to the dorsal carapace of females during mating.

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How is the sex of sea turtles determined?

In sea turtles, sex is not determined by chromosomes from conception as it is with us, but is determined during embryonic development by the average hatching temperature during a particular phase of development. There is a temperature at which about 50:50 females and males are produced, the so-called pivotal temperature. It is about 29.5 °C and can vary somewhat depending on the species and population. Higher temperatures produce more females, lower temperatures produce more males.

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How many eggs do sea turtles lay?

During the nesting season, sea turtles usually lay between four and ten clutches. Some green sea turtles have even laid 12 clutches in one season! Depending on the species and size of the turtle, a clutch generally contains between 70 and 180 eggs. The largest sea turtle – the leatherback – lays about 110 eggs per clutch. Hawksbill turtles produce the largest clutches, with up to 140–160 eggs in one nest!

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How do sea turtles manage to return to the beach of their birth to nest?

The ability to return to the beach of their birth to reproduce after decades of growing up is one of the most fascinating features of sea turtles. The exact mechanisms of this ability are still being researched, but apparently, location-dependent strength and direction of the earth’s magnetic field and a corresponding sense to perceive and also remember them play a significant role in orientation.

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How long does it take for the little sea turtles to hatch from the eggs?

The time from egg laying to hatching is on average about 60 days. Depending on the species and population, but also on the average breeding temperature, there are variations in the absolute and average duration of a couple of days.

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How do the turtle parents take care of the offspring?

The turtle mothers take care of the best possible starting chances for their offspring by suitable choice of the nesting site and by careful building, but also hiding of the nesting burrow. After that, however, the clutches and the young turtles are on their own.

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How many of the young turtles survive after hatching?

By population biological calculations it is estimated that on average of 1,000 hatched turtles only one at a time reaches adulthood and returns to the beach of its birth to reproduce. However, this low chance of survival in the juvenile stage is compensated by nature through a high number of offspring.

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Why do you almost never see very little sea turtles at sea?

On the coasts and the corresponding feeding grounds juvenile turtles can be seen down to the size of a dinner plate, but no smaller animals. For decades, the developmental stage from hatching to dinner plate size remained hidden from scientists (“lost years”). Only recently has it become known that the smaller stages develop on the high seas, where they accompany naturally formed rafts of drift material and passively follow the ocean currents. After several years growing to dinner plate size, the young turtles leave their pelagic environment generally for coastal feeding grounds.

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What are the natural predators of sea turtles?

Sea turtle eggs, hatchlings, and juveniles are subject to numerous natural threats both on land and in the sea. Common predators of sea turtles include fire ants, crabs, monitor lizards and other large lizards, birds, dogs, raccoons, feral hogs, coyotes, dolphins, sharks, and many species of carnivorous fish such as snappers, groupers, and barracuda.

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How do humans doing threaten the survival of sea turtles?

Humans have already significantly reduced the numbers of sea turtles through numerous direct and indirect impacts, certain individual species and populations to the brink of extinction. Not long ago, hunting of the animals and collection of eggs were the most important factors in the decline. In the meantime, however, indirect threats continue to increase, such as by-catch in fisheries, habitat destruction, pollution of the oceans and coasts, and increasingly, the consequences of climate change.

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How can I help protect sea turtles?

Everyone can contribute to reducing man-made pressure on marine ecosystems through sustainable lifestyles. As a tourist visiting the habitats of sea turtles, especially the nesting beaches, it is important to behave in a manner that does not disturb the turtles. Do not buy products made from sea turtles, especially turtle shell products can still be offered locally and on the Internet. Direct help can be provided by conservation organizations such as the Turtle Foundation through a classic donation, a symbolic sponsorship, a purchase of merchandising products (online store of the Turtle Foundation) or by volunteering with us on Boa Vista, Cape Verde).

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