Sea Turtles Of The World

The Seven Species of Sea Turtles of the World

Seven species of sea turtles grace all the world’s oceans, except for the Arctic: the flatback, green, hawksbill, leatherback, loggerhead and olive ridley.  Many species of sea turtle are highly migratory, travelling hundreds or even thousands of miles between foraging and nesting grounds.

Sea Turtles – Ancient Reptiles

Green sea turtle resting on a colourful reef in the Maldives.

Sea turtles have existed on Earth since the days of the dinosaurs. There are currently seven species (or types) of sea turtles, also called marine turtles, but there were once many more. Although each modern sea turtle species is different, having uniquely adapted to different environments and available food, they share many characteristics and all arose from a common ancestor about 110 million years ago.

Turtles belong to the reptile group of animals that also includes snakes, lizards, and crocodiles, all of which share the following characteristics:

  • Scaly skin: this helps reptiles conserve moisture as most of them live in dry, sunny and/or salty environments;
  • Cold-blooded: their body temperature depends on the temperature of their surroundings;
  • Air breathers: all reptiles are born with lungs and use them to get oxygen from the air;
  • Oviparous: they lay eggs (although some snakes, chameleons and lizards give birth to live young).

Turtle, Tortoise, Terrapin – What is the Difference?

Watch the video to learn why all tortoises are turtles but not all turtles are tortoises.

All reptiles with a shell consisting of a top half, the carapace, and a bottom half, the plastron, are called turtles. The shell consists of bone as well as a keratinous layer on top. Depending on the species, bone and keratinous layer can be developed quite differently, as can be seen in e.g. soft- and hard-shelled turtles. There are over 310 species of turtles in the world and they can be divided into three major groups: tortoises, freshwater turtles, or terrapins, and marine turtles.

The term tortoise usually refers to any strictly land-dwelling

turtle, while the word terrapin means “small turtle” and it usually refers to turtles living in fresh and brackish areas, spending their time both on land and in water. The word “turtle” usually refers to those species spending most of their lives in water (either fresh or salty).

Marine turtles can be defined as reptiles with a shell that have adapted to life in the ocean. Some of these adaptations can also be found in terrapins and freshwater turtles, while others are specific to marine animals only.

Sea Turtle Biology

A hawksbill turtle resting on a reef, looking fed up. Image.
A hawksbill turtle resting on a reef, looking fed up.

Sea turtles have a soft or bony shell, flipper-like limbs, and spend 99% of their lives in the ocean. Only adult females temporarily leave the water to lay eggs on land to incubate and hatch successfully. This is the only time in their life when they leave the marine environment. There are some exceptions, however, such as the Hawaiian green turtle population, where both males and females come out of the water to bask along the shore.

All sea turtle species share the general life cycle of turtles, with some small differences. Common for all sea turtles is that their life cycle is quite complex; they depend on the ocean to feed and grow but need sandy beaches to reproduce.

Adaptations For A Life In Water

Front flipper of a sea turtle. Graphic.
A sea turtle front flipper in perfectly shaped for swimming.

The sea turtle body has adapted to life in the sea with a streamlined shell and flippers that allow them to swim quickly. The top shell is called a carapace and the bottom shell is called a plastron. The shell’s surface is smooth and the shape is flat, as opposed to the domed shell of a tortoise.

Their flippers are perfectly shaped to help sea turtles glide through the water. They use their front flippers for propulsion, whereas the back flippers are used more for steering. Females will also use their back flippers to dig holes in the sand when laying eggs.

Furthermore, they can hold their breath for long periods of time, and they hydrate by drinking salt water and expelling the salt from glands behind their eyes.

The Senses of Sea Turtles

Sight

Hawksbill turtle, Laamu Atoll, Maldives. Image.
Hawksbill turtles have excellent underwater vision.

Though near-sighted on land, sea turtles have excellent vision underwater. Their vision includes light within the ultraviolet range and they can see colours, shapes and patterns. On land, marine turtles use visual cues to orientate.

Hearing

Green sea turtle in profile, Maldives. Image.
Green sea turtle in profile showing that they have no outer ears.

Even though sea turtles do not have outer ears, their inner ears can hear low frequencies and sense vibrations. The ecological role of hearing in turtles is not clear. Experiments conducted both underwater and on land revealed that marine turtles respond to sounds in their hearing range with behavioural or physiological changes. Though they do not use hearing to navigate under water, their ears help detect water pressure changes and vibrations that might indicate that a predator is nearby.

Taste & Smell

Green turtle "throat-pumping". Image.
Green turtle seen “throat-pumping”.

Sea turtles have been observed underwater with their nostrils open while slowly opening and closing their mouths. This behaviour is described as “throat-pumping” and is used by turtles to move water towards the nose. Through what is called “chemoreception”, sea turtles analyze the chemicals in the water to find food or to navigate. Chemoreception includes both the senses of taste and smell.

Touch

Green turtle shell, image
The turtle shell is full of nerve endings that are sensitive to pressure.

Very little is known about the sense of touch in sea turtles, but we do know that they are particularly sensitive to touch on the soft parts of their bodies, like their flippers and neck. Sea turtle shells consist of bones, which are covered by a layer of so-called scutes (plates). These scutes are made of keratin, the same material that human fingernails are made of. There are nerve endings enervating even the bones of the shell. These nerve endings are sensitive to pressure, for example from a touch on the back.

Sea Turtles’ Amazing Ability To Navigate

Leatherback hatchling scrambling to the water. ©Joana Hancock. Image.
Leatherback hatchling scrambling to the water. © Joana Hancock.

Maybe the most fascinating trait of sea turtles is their incredible ability to precisely navigate their way back to the area where they were born every few years. Both males and females have this navigational ability.

When turtle hatchlings make their way from their nest to the water, they imprint a type of magnetic signature of that beach into their minds. This signature stays with them for the rest of their lives. Similar to birds, turtles can sense the magnetic field of the earth, which creates a sort of map in their brains.

Arribada. Image.
Arribada © Enrique Perez

The two species of ridley turtles showing synchronized nesting activity, with many thousands of females coming to the beach to nest at the same time, could indicate that turtles also have a precise sense of time. But as many aspects of a sea turtle’s life, this still remains a mystery to science.

Sea Turtles – A Keystone Species

Green turtle on the reef, facing camera, Kenya. Image.
Green turtle on the reef in Kenya.

Sea turtles play an important role in the oceans’ ecosystems, not only in the Indian Ocean, but globally. Their feeding and migratory behaviour influences the abundance of other organisms and thus alters the habitat they live in.

By protecting sea turtles from often man-made threats such as ocean pollution, climate change, coastal development or poaching activities, we can also protect their habitats and the many other marine species sea turtles share them with. And, by extension, we are therefore maintaining the health of the world’s oceans and protecting our selves.

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Sea Turtle FAQ – The Answers to All Your Sea Turtle Questions

Male hawksbill popping head above surface for air, Maldives. Image.
Marvin, male hawksbill, coming up for a breathe, Maldives.

Sea turtles can hold their breath for several hours, depending on their level of activity.

If they are sleeping, they can remain underwater for several hours. In cold water during winter, when they are effectively hibernating, they can hold their breath for up to 7 hours. This involves very little movement.

Although turtles can hold their breath for 45 minutes to one hour during routine activity, they normally dive for 4-5 minutes and surfaces to breathe for a few seconds in between dives.

However, a stressed turtle, entangled in a ghost net for instance, quickly uses up oxygen stored within its body and may drown within minutes if it cannot reach the surface.

Learn More About Sea Turtles – Free Online Courses

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Sea Turtle Science & Conservation

Deep dive into sea turtle science and conservation. Suitable for budding conservationists and those with an interest in the science surrounding turtles, their biology and conservation.

References:

  • Hays GC, Akesson S, Broderick AC, Glen F, Godley BJ, Luschi P, Martin C, Metcalfe JD & Papi F 2001. The diving behaviour of green turtles undertaking oceanic migration to and from Ascension Island: dive durations, dive profiles and depth distribution. Journal of Experimental Biology 204: 4093-4098.
  • Hays GC, Hochscheid S, Broderick AC, Godley BJ & Metcalfe JD 2000. Diving behaviour of green turtles: dive depth, dive duration and activity levels. Marine Ecology Progress Series 208: 297-298.
  • Hochscheid S, Bentivegna F & Hays GC 2005. First records of dive durations for a hibernating sea turtle. Biology Letters 1: 82-86.
  • Lutz PL and Musik JA (eds.) 1996. The Biology of Sea Turtles Volume I. CRC Press.

The actual documentation of a sea turtle’s age in the wild is difficult or nearly impossible. Individual turtles can be tracked for a shorter time of six month to three years with the help of satellite transmitters. Longterm studies rely on capture-recapture principle, just like our turtle photo id project. Each photo of a turtle represents a recapture event documenting that the individual is still alive.

A study of nesting green turtles in Hawaii observed female turtles returning to nest for up to 38 years after they were first identified. Assuming the average age at first nesting activity of 24 years, this would show that green turtles can live to up to at least 62 years.

Similar estimates have been made for loggerhead turtles.

An adult green turtle resting on a reef in Maldives, image
An adult green turtle
Hawksbill turtle resting on the reef, Maldives
An adult hawksbill turtle

References:

  • Dodd C 1988. Synopsis of the biological data on the loggerhead sea turtle. Ecology 88.
  • Humburg IH and Balazs GH 2014. Forty Years of Research: Recovery Records of Green Turtles Observed or Originally Tagged at French Frigate Shoals in Northwestern Hawaiian Islands, 1973-2013. NOAA Technical Memorandum NMFS-PIFSC-40.

When sea turtles are juveniles, it is very difficult to tell their sex by eye as they do not differ externally. However, after reaching sexual maturity male sea turtles develop a long tail, which houses the reproductive organ. The tail may extend past the hind flippers.

Female turtles have a short tail, which generally doesn’t extend more than 10 cm (4 inches) past the edge of the carapace. Male sea turtles (except leatherbacks) have elongated, curved claws on their front flippers to help them grasp the female when mating.

The sex of a sea turtle embryo is determined by the temperature of the sand: warm temperatures result in more females while cooler temperatures result in more males.

Male green turtle tail
Male green turtle tail
Female green turtle tail
Female green turtle tail

The olive and Kemp’s ridley sea turtles are the smallest species, growing only to about 70 cm (just over 2 feet) in shell length and weighing up to 45 kg (100 lbs). Leatherbacks are the largest sea turtles. On average leatherbacks measure 1.5 – 2m (4-6 ft) long and weigh 300 – 500 kg (660 to 1,100 lbs). The largest leatherback ever recorded was 2,56 m (8.4 ft) long and weighed 916 kg (2,019 lbs) !

Kemp’s Ridley

Nesting female kemp's ridley turtle, nicknamed
Nesting female kemp’s ridley turtle, nicknamed “Mij”, laying 116 eggs on Galveston’s East Beach. ©Ron Wooten, Wildscreen Exchange.

55.6-66.0 cm carapace length, weight range of 25-54 kg for nesting females.

References:

  • Marquez-M R 1994. Synopsis of Biological Data on the Kemp’s Ridley Turtle, Lepidochelys kempi (Garman, 1880). NOAA Technical Memorandum NMFS-SEFSC-343.

Olive Ridley

Female Oliver ridley turtle nesting on the beach during arribada
Nesting female olive ridley turtle ©Susie Gibson.

Curved carapace length 52.5-80.0 cm, weight less than 50 kg (average 35.7 kg) for nesting females.

References:

  • Qureshi M 2006. Sea turtles in Pakistan. In: Shanker K and Choudhury BC (Eds.). Marine Turtles of the Indian Sub- continent. Heydarabad: India Universities Press, pp. 217–224.Reichart HA 1993.
  • Reichart HA 1993. Synopsis of biological data on the olive ridley sea turtle Lepidochelys olivacea (Eschscholtz 1829) in the western Atlantic. NOAA Technical Memorandum NMFS-SEFSC-336.

Hawksbills

Adult male hawksbill turtle swimming in the blue, Maldives. Image
Adult male hawksbill, Maldives.

Nesting females reported between 53.3 and 95.5 cm carapace length, with weight between 27.2 and 86.2 kg.

References:

  • Witzell WN 1983. Synopsis of biological data on the hawksbill turtle, Eretmochelys imbricata (Linnaeus, 1766). No. 137. Food & Agriculture Org.

Green turtles

Adult green turtles mating, Malsdives. Image.
Adult green turtles mating, Maldives.

Nesting green females reported curved carapace length 75-134 cm, weight (after egg deposition) 45-250 kg (!).

References:

  • Hirth HF 1997. Synopsis of the Biological Data on the Green Turtle Chelonia mydas (Linnaeus, 1758). Vol. 2. Fish and Wildlife Service, US Department of the Interior.

Flatbacks

Nesting flatback sea turtle ©Lyndie Malan / CC BY-SA.

Ones study (Ref. 1) found nesting females have a mean curved carapace length 86.3 cm, and mean weight of 67.4 kg. Another study (Ref. 2) found flatbacks to be between 87.5-96.5 cm.

References:

  • Schäuble C, Kennett R and Winderlich S 2006. Flatback Turtle (Natator depressus) nesting at Field Island, Kakadu National Park, Northern Territory, Australia, 1990-2001. Chelonian Conservation and Biology 5: 188-194.
  • Limpus CJ 1971. The Flatback Turtle, Chelonia depressa Garman in Southeast Queensland, Australia. Herpetologica 27: 431-446.

Loggerheads

Adult female loggerhead, Oman.

Adult loggerhead turtles measure between 65 and 115 cm in curved carapace length and typically weigh between 40 and 180 kg. The largest recorded loggerhead weighed 545 kg and measured 213 cm in presumed total body length. On average, nesting, and therefore adult, female loggerheads have a curved carapace length of 65.1-114.9 cm and weigh between 40.0 and 180.7 kg. Males fall into the same size range (79.0-104.0 cm curved carapace length).

References:

  • Brongersma LD 1972. European Atlantic turtles. Zoologische Verhandlingen 121, Leiden.
  • Dodd C 1988. Synopsis of the biological data on the loggerhead sea turtle. Ecology 88: 1-119.
  • Ernst CH and Lovich JE 2009. Turtles of the United States and Canada, 2nd edition. John Hopkins University Press.

Leatherbacks

Leatherback Turtle, Claudia Lombard, USFWS
Adult leatherback turtle ©Claudia Lombard, USFWS.

143.8-169.5 cm curved carapace length, weight 259-506 kg recorded for nesting females all around the world. Largest ever recorded specimen was found dead on a beach on the coast of Wales. The adult male turtle weighed 916 kg and its shell was 256.5 cm long. An autopsy revealed that it had drowned.

References:

  • Eckert KL and Luginbuhl C 1988. Death of a Giant. Marine Turtle Newsletter 43: 2-3.
  • Eckert KL, Wallace BP, Frazier JG, Eckert SA and Pritchard PCH 2012. Synopsis of the Biological Data on the Leatherback Sea Turtle (Dermochelys coriacea). Biological Technical Publication BTP-R4015-2012, US Fish & Wildlife Service.

Each sea turtle species feeds on a specific diet and all lack teeth:

  • Flatbacks are mainly carnivorous turtle feeding in shallow waters on soft bottoms.
  • Green turtles are vegetarian and prefer sea grasses, sea weeds and algae as adults, however, green turtle hatchlings are omnivorous, eating jellyfish, snails, crabs, and shrimp.
  • Hawksbills have a bird-like beak that is used to cut through soft coral, anemones and sea sponges.
  • Kemp’s ridleys are omnivores at the beginning of their lives, feeding on seaweed and small creatures like crabs and snails. As adults, Kemp’s ridleys look for food on the seabed, feeding on crustaceans, fish, molluscs, squids and jellyfish.
  • Leatherbacks feed mostly on jellyfish.
  • Loggerheads feed mainly on hard-shelled organisms such as lobsters, crustaceans, and fish.
  • Olive ridleys are omnivorous, mostly eating jellyfish, snails, crabs, and shrimp but they will occasionally eat algae and seaweed as well.

Learn More About Sea Turtles – Free Online Courses

Free

e-Turtle School – All About Sea Turtles

Everything you have ever wanted to know about sea turtles, from evolution to conservation. Suitable for all sea turtles lovers and those who want to learn more about these fascinating creatures.
Free

Sea Turtle Science & Conservation

Deep dive into sea turtle science and conservation. Suitable for budding conservationists and those with an interest in the science surrounding turtles, their biology and conservation.

Enroll Today And Learn More About Sea Turtles:
Free Online Courses

Free

e-Turtle School – All About Sea Turtles

Everything you have ever wanted to know about sea turtles, from evolution to conservation. Suitable for all sea turtles lovers and those who want to learn more about these fascinating creatures.
Free

Sea Turtle Science & Conservation

Deep dive into sea turtle science and conservation. Suitable for budding conservationists and those with an interest in the science surrounding turtles, their biology and conservation.

References:

  • Bickham JW, Iverson JB, Parham JF, Philippen HD, Rhodin AGJ, Shaffer HB, Spinks PQ and van Dijk PP 2007. An Annotated List of Modern Turtle Terminal Taxa with Comments on Areas of Taxonomic Instability and Recent Change. Chelonian Research Monographs 173: 173-199
  • Dodd C 1988. Synopsis of the biological data on the loggerhead sea turtle. Ecology 88: 1-119.
  • Eckert KL, Wallace BP, Frazer JG, Eckert SA and Pritchard PCH 2012. Synopsis of the Biological Data on the Leatherback Sea Turtle (Dermochelys coriacea). Biological Technical Publication BPT-R4015-2012, US Fish & Wildlife Service.
  • Guillette LJ 1993. The Evolution of Viviparity in Lizards. BioScience 43: 742-751.
  • Harry JL and Briscoe DA 1988. Multiple paternity in the loggerhead turtle (Caretta caretta). The Journal of Heredity 79: 96-99.
  • Hirth HF 1997. Synopsis of the Biological Data on the Green Turtle Chelonia mydas (Linnaeus, 1758). Vol 2. Fish and Wildlife Service, US Department of the Interior.
  • Hudgins J, Mancini A and Ali K 2017. Marine Turtles of the Maldives: A field identification and conduct guide. An IUCN Publication funded by USAID.
  • Lee PLM and Hays GC 2004. Polyandry in a marine turtle: Females make the best out of a bad job. PNAS 101: 6530-6535.
  • Lohmann KJ, Lohmann CMF, Ehrhart LM, Bagley DA and Swimg T 2004. Geomagnetic map used in sea-turtle navigation. Nature 428: 909-910.
  • Piniak WED, Mann DA, Harms CA, Jones TT and Eckert SA 2016. Hearing in the Juvenile Green Sea Turtle (Chelonia mydas): A Comparison of Underwater and Aerial Hearing Using Auditory Evoked Potentials. PLoS One: DOI:10.1371/journal.pone.0159711 1-14.
  • Reichart HA 1993. Synopsis of biological data on the olive ridley sea turtle Lepidochelys olivacea (Eschscholtz 1829) in the western Atlantic. NOAA Technical Memorandum NMFS-SEFSC-336.
  • Schäuble C, Kennett R and Winderlich S 2006. Flatback Turtle (Natator depressus) Nesting at Field Island, Kakadu National Park, Northern Territory, Australia, 1990-2001. Chelonian Conservation and Biology 5: 188-194.
  • Spotila JR 2004. Sea Turtles: A Complete Guide to Their Biology, Behaviour and Conservation. The John Hopkins University Press, Baltimore, USA. Whittow G and Balasz G 1982. Basking Behaviour of the Hawaiian Green Turtle (Chelonia mydas). Pacific Science 36: 129-139.
  • Witzell WN 1983. Synopsis of biological data on the hawksbill turtle, Eretmochelys imbricata (Linnaeus, 1766). No. 137. Food & Agriculture Org.
  • Wyneken J 2001. The Anatomy of Sea Turtles. NOAA Technical Memorandum NMFS-SEFSC-470.

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