Sea turtles have navigated the Earth’s oceans for over 100 million years, even witnessing the rise and fall of dinosaurs. These marine reptiles, found in tropical and subtropical seas worldwide, embark on epic migrations across ocean basins in search of food. Though they spend almost their entire lives underwater, females periodically emerge onto the same sandy beaches where they were born to lay their eggs.
Yet, these ancient mariners face a myriad of threats in the modern world. Entanglement in fishing gear, habitat loss due to coastal development, and the persistent poaching of their eggs and meat continue to undermine global conservation efforts.
In this blog, we’ll uncover the seven biggest sea turtles that navigate our oceans and learn more about their unique characteristics and the challenges they face.
Kemp’s Ridley
Size: Out of all sea turtles, the Kemp’s Ridley is the smallest, only growing to be about 2 feet long and weighing 70 to 100 pounds.
Where are they found: Kemp’s Ridley sea turtles are primarily found in the Gulf of Mexico and occur less frequently throughout the Atlantic Ocean, as far north as Nova Scotia.
The world’s smallest sea turtle, and the most endangered, the Kemp’s Ridley (Lepidochelys kempii), is named for Richard M. Kemp, a fisherman from Florida who first submitted the species for identification over a century ago.
The Kemp’s ridley sea turtle has a distinctive triangular head and a slightly hooked beak. Its shell is generally grayish-green on top and pale yellow underneath, often being as wide as it is long. They are renowned for their daytime nesting behavior and mass nesting events called “arribadas,” where hundreds of females gather to lay their eggs simultaneously. These turtles spend their first years drifting with Sargassum algae before migrating to coastal areas where they primarily feast on crabs.
The Kemp’s Ridley sea turtle faces a multitude of threats, most notably bycatch, habitat loss, and predation. These are compounded by issues such as illegal egg collection, vessel strikes, pollution, and the impacts of climate change.
Olive Ridley
Size: Olive Ridley sea turtles are typically between 2 and 2.5 feet long and weigh up to 100 pounds.
Where are they found: Olive Ridley sea turtles have a global distribution favouring pelagic habitats in tropical to temperate waters.
Olive Ridleys (Lepidochelys olivacea) are small sea turtles with an olive to grayish-green body color and a distinctive heart-shaped carapace. Interestingly, the size and shape of these sea turtles can differ depending on their geographical location, with the biggest sea turtles found in the waters off West Africa.
They share a similar appearance with Kemp’s ridley turtles and are also known to nest in synchronous mass events called “arribadas“. Sadly, rising sea levels caused by climate change will likely harm Olive Ridley sea turtle populations by shrinking nesting beaches and making it harder for eggs to hatch successfully.
They are listed as Vulnerable on the IUCN Red List of Threatened Species and have a decreasing population trend. Threats to their survival include bycatch, direct harvest, habitat loss, predation, vessel strikes, and pollution.
Hawksbill
Size: Hawksbill sea turtles can reach up to 3.5 feet long and weigh up to 150 pounds.
Where are they found: Hawksbill sea turtles have a global distribution from temperate to tropical waters, preferring nearshore habitats, especially coral reefs.
Hawksbill sea turtles (Eretmochelys imbricata) are easily recognized by their beautifully mottled carapace, showcasing a variety of colors from amber to black. Their carapace also has a unique serrated edge with overlapping scutes. Adding to their distinctive look, their tapered heads and V-shaped jaws give them a hawk-like appearance, hence their name.
These sea turtles stand out for their specialized diet of sea sponges, which they access with their sharp beak, allowing them to reach into crevices in coral reefs. Hawksbill sea turtles migrate great distances between their feeding grounds and nesting beaches.
Hawksbill sea turtles are Critically Endangered and have a decreasing population trend. This species is threatened by a variety of human-induced and environmental factors. From accidental capture in fishing gear (bycatch), illegal hunting for their shells and eggs, and habitat degradation of their nesting and foraging grounds due to coastal development and climate change.
Australian Flatback
Size: The Australian Flatback sea turtle can grow to be up to 3 feet long and weighs 200 pounds.
Where are they found: Australian Flatback sea turtles are found in the tropical waters surrounding Australia and Papua New Guinea.
The Australian flatback (Natator depressa) has a flat body with a smooth, nearly elliptical carapace that has upturned edges in adults. Its head is medium-sized with a longer nose. Adults are dull olive-grey with a pale underside. Young turtles are brighter, with hatchlings having a patterned carapace with cream-colored bands on their bodies.
Global population estimates are unavailable, but genetic studies identify four distinct stocks in Australia. These stocks face varying levels of threat, with only some considered stable and others showing signs of decline. Unfortunately, Australian Flatback sea turtles face threats from various human activities and environmental factors.
These threats can be broadly categorized as fishing (incidental capture in nets, entanglement in ghost nets), coastal infrastructure and development (light pollution, habitat degradation, boat strikes), indigenous harvest, animal predation, and climate change-related impacts.
Loggerhead
Size: Loggerhead sea turtles can grow to be 3.5 feet long and weigh up to 350 pounds.
Where are they found: Loggerhead sea turtles have a global distribution with a preference for subtropical to temperate waters.
Loggerhead sea turtles (Caretta caretta) are known for their large heads and powerful jaws, which enable them to crush their prey. They are carnivorous feeding on invertebrates such as horseshoe crabs and mollusks. Their carapace is reddish-brown and slightly heart-shaped.
Loggerhead sea turtles embark on trans-Pacific migrations, traveling up to 8,000 miles between their feeding and nesting grounds. Hatchling sea turtles spend their early years in the open ocean before transitioning to coastal waters as they mature.
Like most other sea turtles, Loggerheads also suffer from habitat loss due to coastal development and climate change, vessel strikes in high-traffic areas, and the lingering issue of direct harvest in some regions. Additionally, ocean pollution like balloons and plastic bags poses risks of ingestion whilst marine debris pose risks of entanglement. In addition, climate change affects nesting success, food availability, and overall habitat suitability.
Green
Size: One of the biggest sea turtles, Green sea turtles reach up to 4 feet long and can weigh up to 400 pounds.
Where are they found: Green sea turtles are found worldwide, from tropical to temperate regions.
Green sea turtles (Chelonia mydas) are not only the biggest hard shell sea turtle in the world but also rank among the biggest sea turtles overall, second only to the Leatherback. They have a distinctive small head compared to their large bodies, with a serrated beak. Their shells are typically dark brown, grey, or olive on top with a lighter underside.
Green sea turtles stand out as the only herbivorous sea turtle species, feeding mostly on algae and seagrasses. Although their diet also includes sponges and invertebrates, it is their plant diet that gives their fat a unique greenish tint, earning the name “green turtle.”
Despite their increasing population trend, Green sea turtles remain Vulnerable to several human and environmental threats. These include accidental capture in fishing gear (bycatch), illegal hunting for their meat and eggs, and the destruction of nesting beaches due to coastal development and rising sea levels caused by climate change.
Sadly, Fibropapillomatosis is a disease causing debilitating tumors in green sea turtles. This disease can severely impact their survival by hindering swimming and feeding, and is often linked to environmental degradation.
Leatherback
Size: The Leatherback is the biggest sea turtle, reaching an impressive size of 5 to 6 feet in length and weighing between 750 and 1,000 pounds.
Where are they found: The Leatherback sea turtle has circumglobal distribution, nesting on tropical beaches and feeding in temperate to sub-polar waters.
Leatherback sea turtles (Dermochelys coriacea) are easily distinguished by their black, rubbery skin and the absence of scales, setting them apart from other sea turtles. They have a unique carapace composed of small, interlocking bones beneath their leathery skin, contributing to their streamlined shape.
Unlike other sea turtles, Leatherbacks are capable of diving to depths of up to 4,000 feet. Staying underwater for up to 85 minutes, they feed on soft-bodied prey like jellyfish, salps and siphonophores.
Leatherback sea turtles face a range of serious threats, including accidental capture in fishing gear, poaching of adults and eggs, loss of sand for nesting habitat due to coastal development and climate change, vessel strikes, ingestion and entanglement in marine debris, and the wider effects of climate change on their food supply and nesting areas.
Ocean Insights: Hear From Our Experts
By Dr. Rabiah Ryklief
Principal Scientist and Lecturer of Marine Science, with a PhD in Zoology
Sea turtles are facing a grave threat due to the multiple impacts of climate change. From rising sea levels inundating nesting beaches, to increased storm intensity causing habitat erosion and shifts in ocean temperatures affecting hatchling sex ratios and food availability. These changes threaten the survival of sea turtle populations globally, highlighting the urgent need to reduce the anthropogenic impacts on the climate. Addressing the root cause of these threats is critical, requiring mitigation efforts such as legislation to protect sea turtles and the expansion of marine protected areas to encompass their habitats under future climatic conditions.
FAQs
How do Leatherback sea turtles eat?
Leatherback sea turtles have unique adaptations that allow them to thrive on a diet of jellyfish and other soft-bodied creatures. Their sharp-edged jaws and pointed cusps are perfect for grabbing and slicing prey, while backward-pointing spines lining their mouth and throat help them hold onto slippery jellyfish. These spines in the throat also ensure that swallowed prey doesn’t escape back up.
How are Leatherback sea turtles adapted to cold water?
Leatherback sea turtles are uniquely adapted to thrive in cold water due to a combination of factors that help them maintain their body temperature. Their large size, modified swimming activity and blood flow, and a thick layer of insulating fat all contribute to their ability to generate and conserve heat, allowing them to stay comfortable even in frigid ocean environments.
How long can sea turtles live?
Sadly, few sea turtles survive into adulthood. Baby sea turtles face many threats once they’ve hatched, including disorientation while trying to make it into the ocean as well as predators like snakes and birds. But for those that do make it to adulthood, sea turtles live, on average, between 50 and 100 years. In addition to their lengthy lifespans, sea turtles are also among the oldest creatures on the earth — they’ve been around for more than 100 million years.
