Green Sea Turtle

Reptiles of Ecuador | Testudines | Cheloniidae | Chelonia mydas

English common names: Green Sea Turtle, Pacific Green Turtle, Black Turtle.

Spanish common name: Tortuga verde, tortuga prieta, tortuga negra.

Recognition: ♂♂ 104.1 cmThis is a measurement of the straight length of the carapace. ♀♀ 153 cmThis is a measurement of the straight length of the carapace.. The Green Sea Turtle (Chelonia mydas) may be distinguished from other sea turtles by having four pairs of costal shields, one pair of prefrontal scales, and non-overlapping carapace shields. Males are distinguished from females by having longer, thicker tails. In the Galápagos Archipelago, two genetically distinct morphs of Chelonia mydas coexist: the black morph and the yellow morph. Black Turtles are dark olive green in coloration and are larger than Yellow Turtles, which are light orangish brown in coloration.

Natural history: Extremely common. Chelonia mydas is the most common sea turtle in Galápagos1 and the second most common along the coast of mainland Ecuador.2 In Galápagos, turtles of the black morph are generally more abundant than those of the yellow morph. After hatching on tropical beaches, hatchlings of the Green Sea Turtle frantically swim for 1–3 days in an offshore direction until they reach open ocean "nursery" habitats where they spend 3–10 years3 actively swimming and drifting day and night along with surface currents.4 During this early stage, they are mainly carnivorous,5 feeding on comb jellies, pelagic tunicates, worms, molluscs, crustaceans, and insects, but also on seagrasses and algae.6,7

Green Sea Turtle hatchlings worldwide are preyed upon by a variety of mammals (including pigs, foxes, cats, mongooses, coatis, and rats), birds (such as sea birds, vultures, and crows), snakes, sharks, fish, and crabs.1,8 When they reach 20–35 cm in length, they establish their home ranges in shallower waters near the coast,5 where they become largely herbivorous,5 spending most of the day around areas of good pasturage, grazing on a variety of seagrass and algae species7 as well as on leaves, tree bark, saltgrass, and animal matter such as tube worms, crustaceans, bryozoans, fish and their eggs, tunicates, jellyfish, echinoderms, molluscs, and sea sponges.8–11

Green Sea Turtles spend most of the day conducting shallow (less than 20 m deep) dives12 and resting on the water surface,13 but they can dive down to 138 m in depth14 and for up to 70 minutes.15 Occasionally, adults bask on shore16 during the daytime if sea surface temperatures fall below 23 °C.17 At night, they rest near the surface,13 or on the sea bottom, or among rocks or coral crags18 at a depth of 18–20 m.12 Some adults of Chelonia mydas are permanent residents of coastal waters (usually within 15 km from the nesting beaches), while others are migratory,18 traveling up to 90 km per day,19 and up to a total of 8,283 km to distant foraging grounds.20 Using geomagnetic cues,21 females routinely travel thousands of kilometers to return to nest at or near the same beaches season after season, which may also be the same beaches on which they themselves hatched.22

In the Galápagos Archipelago, some Pacific Green Turtles, also known as Black Turtles, reside permanently around the islands, but others migrate, either into oceanic waters, or into shallow foraging waters near mainland Central and South America.23,24 Most Green Sea Turtles on the coast of mainland Ecuador breed and feed locally,25,26 but some also travel to Galápagos and presumably elsewhere along the eastern Pacific.27,28 Turtles of the yellow morph do not nest in Galápagos; they do so in nesting grounds in the Indo-Pacific.

Green Sea Turtles become sexually mature around 17–19 years old. From this age onwards, they gather in polygamous29 breeding rookeries within ~1 km from the nesting beaches,30 where pairs may copulate for up to 6–24 hours.1 Hybridization between Chelonia mydas and other sea turtle species such as Caretta caretta,31 Eretmochelys imbricata,32 and Lepidochelys olivacea,32 occurs. Females of the Green Sea Turtle are capable of storing sperm throughout the breeding season,29 and the resulting clutches may be sired by multiple males.29 They nest every 2–4 years19 on roughly (0.4–1.2 km apart)8 the same beaches.

In Ecuador, Black Turtles nest throughout the year,1 but most nest from November to May with a peak from February to March.30,33 During a single season, females may lay 1–9 clutches19,34 at intervals of 5–25 days.35 They produce 18–226 eggs8 per clutch and lay them on sandy beaches in 56–77 cm deep nests,18,36 usually at night.18 Nesting emergences last 2–3 hours.8 During these events, female Green Sea Turtles are very shy, and can easily be scared back into the sea.8 Nesting may be solitary (as it is in Ecuador) or in huge aggregations, with up to 11,755 females nesting in the same area during a single night.37 The incubation period is 40–99 days,7 and 1–89.9% of the eggs laid on Ecuadorian beaches hatch.1,30 Temperature determines the sex of the offspring,38 and the proportion of female hatchlings increases with the incubation temperature.39 Nest temperatures >30.3ºC produce females and temperatures <28.5ºC generate males.40

Eggs of Pacific Green Turtles in Galápagos are mostly preyed upon by pigs and beetles.1,41 On mainland Ecuador, they are eaten by dogs and raccoons.42 Worldwide, they are preyed upon by a variety of mammals (including peccaries, pigs, dogs, foxes, jackals, opossums, raccoons, coatis, and rats), birds (including birds of prey, vultures, ibises, and crows) monitor lizards, crabs, beetles, and ants.8,35,43 They are also occasionally lost to flooding44 and disturbance by other nesting turtles, in addition to being widely used for human consumption.45 The eggs of Chelonia mydas hatch synchronously46 and usually at night.1,18 During emergence, the presence of artificial lighting affects the orientation of hatchlings,47 which may result in mortality caused by traffic. It is estimated that only 1–3% of hatchlings survive into adulthood.8

In addition to predation by sharks,48 crocodiles,7 and jaguars,49 causes of mortality for adult Green Sea Turtles include ingestion of plastic,50 collision with boats,51–53 interactions with fishing gear,54,55 direct harvesting for meat consumption (although their meat may cause food poisoning),2,45 oil spills,55 red tides,56 and cyclones.7 Individuals of Chelonia mydas are parasitized by a variety of worms and leeches, and colonized by remoras, barnacles, crabs, amphipods, mussels, isopods, sea snails, hydrozoans, bryozoans, and algae.7,8 The lifespan of individuals of C. mydas in the wild is about 80 years, but, based on growth rates,57 we estimate a maximum lifespan of 118 years.

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Conservation: Endangered.58 Chelonia mydas is listed in this category because its populations have declined 48–67% over the past three generations as a result of the direct harvesting of eggs and adults, incidental mortality due to interactions with artisanal and industrial fisheries, and the degradation of marine and nesting habitats.58 Another threat faced by C. mydas is climate change. Since temperature during incubation determines the sex of the offspring,38 the increase of the average global temperature may result in the complete feminization of some populations.39 Under some scenarios of global sea level rise, up to 60% of clutches on some nesting beaches may be lost to flooding by 2100.59

Distribution: Green Sea Turtles occur throughout the entire tropical Atlantic, Indian, and Pacific oceans. The morph known as Black Turtle is restricted to the Pacific Ocean.

Distribution of Chelonia mydas along mainland Ecuador Distribution of Chelonia mydas in Galápagos

Etymology: The generic name Chelonia comes from the Greek word chelone (meaning “turtle”).60 The specific epithet mydas is a reference to the Greek king Midas, who had the ability to turn everything he touched into gold.60

See it in the wild: Individuals of Chelonia mydas can be seen year-round with ~80–100% certainty in shallow waters throughout Galápagos. Swimming Green Sea Turtles can be easily observed from the coast, while snorkeling or diving, or from boats going to and from tourism sites. Along the coast of mainland Ecuador, the Green Sea Turtle is harder to see. Although the species nests roughly on the same beaches during the same months, witnessing such events is rare. However, swimming Chelonia mydas can be seen with ~60–80% certainty in shallow waters off Machalilla National Park, especially in Isla de la Plata.

FAQ

Do sharks eat Green Sea Turtles? Yes.48 Sharks are among the few predators of adult Green Sea Turtles.

Do Green Sea Turtles bite? Yes. Although Green Sea Turtles do not feed on humans, there have been cases of turtles biting swimmers.61 These bites may be painful, but are not life-threatening.

How big do Green Sea Turtles get? Green Sea Turtles can grow up to 1.53 m in straight carapace length.

How fast do Green Sea Turtles swim? Green Sea Turtles can swim at a speed of 3.6 km/h over short distances62 and they can maintain a long-distance cruising speed of up to 65 km/d.63 Michael Phelps' top swimming speed is 9.7 km/h.

How long do Green Sea Turtles live? The average lifespan of Green Sea Turtles in the wild is about 80 years, but, based on growth rates,57 they may live up to 118 years.

What does a Green Sea Turtle eat? Green Sea Turtles are mainly herbivores, feeding mostly on seagrass and algae species, but also on leaves, tree bark, saltgrass, and animal matter.8–11

When and where do Green Sea Turtles sleep? Green Turtles usually sleep at night. They do so near the surface,13 on the sea bottom, or among rocks or coral crags18 at a depth of 18–20 m.12

Where do Green Sea Turtles come from? Green Sea Turtles occur throughout the entire tropical Atlantic, Indian, and Pacific oceans. The morph known as Black Turtle is restricted to the Pacific Ocean. The morph known as Black Turtle is restricted to the Pacific Ocean, whereas the morph known as Yellow Turtle comes from nesting grounds in the Indo-Pacific.

Why are Green Sea Turtles Endangered? Green Sea Turtles are classified as Endangered because their populations have declined 48–67% as a result of the direct harvesting of eggs and adults, incidental mortality due to interactions with artisanal and industrial fisheries, and the degradation of marine and nesting habitats.58

Why are Green Sea Turtles green? The skin and carapace of Green Sea Turtles is not really green, but reddish brown or dark olive. The green color comes from algae living on the turtles. However, Green Sea Turtles are named after their greenish-colored fat, which is believed to be a result of their herbivorous diet.


Special thanks to Jack W. Sites, Jr. for symbolically adopting the Green Sea Turtle and helping bring the Reptiles of Ecuador book project to life.

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Authors: Alejandro ArteagaaAffiliation: Khamai Foundation, Quito, Ecuador. and Juan M GuayasaminbAffiliation: Laboratorio de Biología Evolutiva, Universidad San Francisco de Quito (USFQ), Quito, Ecuador.,cAffiliation: Galapagos Science Center, Galápagos, Ecuador.,dAffiliation: Centro de Investigación de la Biodiversidad y Cambio Climático, Universidad Tecnológica Indoamérica, Quito, Ecuador.

Academic reviewers: Graeme Hays and Juan José Alava.

Photographers: Jose VieiraaAffiliation: Tropical Herping (TH), Quito, Ecuador.,eAffiliation: ExSitu, Quito, Ecuador. and Alejandro ArteagaaAffiliation: Tropical Herping (TH), Quito, Ecuador.

How to cite? Arteaga A (2020) Chelonia mydas. In: Arteaga A, Bustamante L, Vieira J (Eds) Reptiles of Ecuador: Life in the middle of the world. Available from: www.reptilesofecuador.com

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