There's something quite mesmerising about sea turtles, their fascinating lives and the perils they face, from poaching to predators.
Learn all about the seven different types of sea turtle, five of which have been recorded in British waters, including leatherback, loggerhead, kemp’s ridley, green, and hawksbill.
Sea turtle types
Green turtle
Chelonia mydas
Global population: Estimated vary widely, possibly around 200,000; decreasing.
Conservation status: Endangered
Size: 1.5m length
Weight: up to 190 kg
Maturation and longevity: May take 20 or more years to reach reproductive age, possibly up top 80 years in some populations.
Description: Several different ‘types’ of Green turtles inhabit different regions of the world, ranging from the large, dark form often referred to as ‘black turtle’ frequenting Hawaii, Central America and Galapagos, to the pale yellow morph found in the central Pacific, and amber-coloured varieties in the Caribbean and Indian Ocean.
Diet: Hatchlings and juveniles are primarily carnivorous, eating pelagic invertebrates and fish eggs near the surface in open ocean and among rafts of floating sargassum and other seaweed. Adults become almost exclusively vegetarian, grazing many types of tender seaweed and seagrass meadows, also mangrove shoots.
Range: All tropical and subtropical seas of the world, nesting in tropical climates.
Life history: Nest mainly on islands, but also on continental beaches, with eggs buried in sandy where they incubate under the sun for 50-70 days. Clutch size varies between populations, 85-200 eggs per clutch, with several nests laid in a season. Young spend 3-5 years at sea before taking up residence in the shallows to graze, but may swim thousands of kilometres to return to nest on the same beach where they hatched.
Loggerhead sea turtle
Caretta caretta
Conservation status: Vulnerable
Global population: World’s most common sea turtle species. Estimates vary widely between 200,000 and 2,000,000; decreasing.
Size: 1.6m length
Weight: up to 200 kg
Maturation and longevity: Maturity may not be reached until 30 years or so, with life expectancy estimated 50-60 years.
Description: The leatherback turtle is a chunky turtle with yellowish-orange and dark rusty red tints, relatively short flippers, and exceptionally muscular jaw for crushing hard prey. Neck skin and underside mostly pale.
Diet: Sizeable benthic invertebrates of all types, such as conchs, sea cucumbers, sea urchins, starfish, crabs and many others, as well as jellyfish in open waters.
Range: Cosmopolitan seas, but mostly in northern hemisphere, with distinct preference for coastal, sub-tropical waters, migrating to temperate regions in summer. It is capable of partial hibernation in cold temperatures by resting on the bottom and rising to breathe only a few times a day.
Life history: Nests on tropical beaches but mostly in cooler regions than other turtles, with clutch size averaging well over 100 eggs; several nests per season laid at roughly two-weekly intervals. Incubation around 80 days.
Hawksbill
Eretmochelys imbricata
Conservation status: Critically endangered
Global population: Estimated around 50,000 to 80,000; decreasing.
Size: 1m
Weight: 80kg average
Maturation and longevity: Adulthood is reached between 10-25 years in the Caribbean, but longer in the Pacific. Longevity is unknown, but estimated between 50-60 years.
Description: Exceptionally thick, overlapping plates cover the entire shell, producing a serrated edge to its margins. Front flippers narrow and agile, as well as long, mobile neck and pointed beak-like jaws allow it to seek food in coral reef recesses. The reddish and amber-streaked shell plates have been traded for centuries, used for jewellery, eyeglass rims and many other trinkets known generically as ‘tortoiseshell’.
Diet: Mainly feed on sponges despite these being packed with sharp silica spicules which implant the turtle’s gut lining, as well as other highly toxic invertebrates. Jellyfish and sea anemones are also taken despite their powerful stinging cells.
Range: Frequents all tropical coral reefs of the world, but may cross vast stretches of ocean to reach natal nesting grounds.
Life history: Shy, biannual nester frequenting small beaches on many dispersed islands, usually digging its nest, which is shallower than other species, under cover of coastal vegetation. Clutch size 120-160 eggs, with up to six nests per season; incubation about 60 days.
Olive Ridley
Lepidochelys olivacea
Conservation status: Vulnerable
Global population: Unknown; decreasing.
Size: 0.6-0.8m length
Weight: 30-50 kg
Longevity: Unknown, but estimated 30-50 years.
Description: Rather graceful shape, flattish with slightly convex slopes to its back, especially in males, enables it to plane weightlessly in midwater, with sharp cutting beak to grasp pelagic invertebrates. Greenish-tan colour gives rise to its name, but plastron is pale yellow, slightly concave in males.
Diet: Salps, jellyfish, oceanic crustaceans & molluscs, fish eggs and many other mid-water invertebrates.
Range: Nearshore tropical and subtropical waters of the world, yet does not approach land except to nest.
Life history: Most notable trait is massive, coordinated nesting, known as ‘arribada’ (Spanish for arrival), when several hundred thousand females nest simultaneous over 2-3 days on a short stretch of beach. Usually taking place around the new moon, this behaviour helps to drown out predator pressure, since it’s main nesting beaches are continental.
However, large numbers of eggs are destroyed by females digging out each other’s nests. Clutch size varies, but averages slightly over 100 eggs per nest, laying between one and three times per season. Incubation is short, around 45-50 days, yet not short enough to avoid damage from the next arribada, timed by the moon cycle.
Kemp’s Ridley turtle
Lepidochelys kempi
Conservation status: Critically endangered
Global population: Estimated 25,000; possibly increasing.
Size: 0.6-0.8m length
Weight: 30-45 kg
Maturation and longevity: Early maturity at 10-12 years, but lifespan not known.
Description: Oddly pale, with predominantly whitish underpart, neck and head, but darker gray carapace; regarded as the smallest of all sea turtles, yet only marginally so compared to its close cousin, the Olive Ridley. Oval carapace is almost as wide as it is long.
Diet: Molluscs, crustaceans, fish, jellyfish.
Range: Very restricted range, Gulf of Mexico, straying up eastern North American seaboard.
Life history: Nearly driven to extinction half a century ago; protective legislation has miraculously brought back the historic arribadas at Rancho Nuevo, Mexico. Translocation of nests to Texas has further boosted prospects for this range-limited species. Clutch size about 100 eggs, renesting up to four times at 10-20 days interval. Young live in floating sargassum for several years before dispersing.
Flatback turtle
Natator depressus
Conservation status: Data deficient
Global population: Estimated 69,000; trend unknown.
Size: 1 m length
Weight: 70-90 kg
Maturation and longevity: Unknow, but lifespan possibly up to 50 years.
Description: Pale olive-green, remarkably round shell, unusually thin and brittle, with distinctly upturned edges. Rounded, stubby head. Unlike other sea turtles, females are larger and have longer tail than males.
Diet: Mainly carnivorous, eating shallow water invertebrates like sea cucumbers, molluscs, shrimp and other marine invertebrates.
Range: Shallow waters on continental shelf, mainly northern coast of Australia as far as New Guinea and southern Indonesia.
Life history: Lays on average 50 eggs, up to four times per season, about two weeks apart. Eggs and hatchlings larger than other turtles at 5.5cm and 6cm respectively, staying close to shore in early life unlike other species. Adults spend much time in turbid water feeding along muddy seafloor.
Leatherback turtle
Dermochelys coriacea
Conservation status: Vulnerable, but Critically endangered in Pacific Ocean.
Global population: Estimated 30,000 to 40,000; decreasing sharply.
Size: 2 m
Weight: 500-700 kg
Maturation and longevity: Lifespan unknown, estimated 50-100 years.
Description: The leatherback turtle is the only species in family Dermochelyidae, almost unchanged for 110 million years, a real dinosaur amongst us. Cylindrical body with five sharp longitudinal ridges on back. Leathery skin instead of shell, embedded with minuscule bony plates called osteoderms. Dark grey or bluish-black with variable pale dots and smudges; pinkish throat and blotch on top of skull, regarded as light-sensitive ‘parietal eye’.
Diet: Primarily pelagic jellyfish, especially giant forms such as lion’s mane jelly found in cold water regions. Mouth, throat and oesophagus lined with sharp inward-facing spikes (papillae) to facilitate swallowing slippery prey.
Range: Most widespread of all turtles (and all reptiles). Pelagic in all oceans of the world, reaching subarctic waters in summer. Returns to tropical shores to nest, often crossing entire ocean basins, up to 20,000 km round-trip.
Life history: Teardrop body shape and powerful front flippers enable cruising speed over 8 kph and diving to 1,200m depth. The only reptile to produce metabolic heat (endothermy), plus countercurrent heat-exchange circulatory system allows body temperatures up to 18°C higher than surrounding water. Lays every 2-5 years, with repeat nesting at 10 days interval. Nest 75 cam deep in wet sand; clutch size around 65-115 eggs measuring 5.3 cm in diameter. Incubation 60-70 days, hatchlings just over 6cm long.
Tui De Roy is a renowned wildlife photographer and author raised in the Galápagos Islands. Her next title on all sea turtles of the world is due in 2024. See tuideroy.com.