Sea turtles are ancient, fascinating marine reptiles that have navigated the world’s oceans for over 100 million years. These remarkable creatures inhabit tropical and subtropical waters across the globe, undertaking vast migrations between feeding grounds and nesting beaches. Although they spend most of their lives in the ocean, adult females return to land to lay their eggs.
Identifying the Seven Species
The Loggerhead sea turtle (Caretta caretta) is identifiable by its large head and powerful jaws, suited for crushing prey like crabs and conchs. Its carapace typically exhibits a reddish-brown coloration, and it can weigh around 135 kilograms, with some individuals exceeding 450 kilograms. Loggerheads are found globally in temperate and tropical waters, often migrating thousands of miles across ocean basins. Their diet is omnivorous.
The Green sea turtle (Chelonia mydas) is named not for the color of its shell, which ranges from olive to black, but for the greenish hue of its body fat. As adults, they primarily consume seagrass and algae, possessing a serrated jaw adapted for this vegetation, though juveniles are omnivorous. These turtles are widespread in tropical and subtropical seas, frequently inhabiting shallow coastal waters rich in seagrass beds. They are the only species within their genus.
The Leatherback sea turtle (Dermochelys coriacea) is the largest of all sea turtle species, distinguished by its unique, leathery carapace instead of a hard, bony shell. This flexible, rubbery skin is supported by thousands of tiny bone plates. Leatherbacks are highly migratory, traversing vast expanses of the Atlantic and Pacific Oceans, and are known for their deep dives in search of jellyfish. They possess the widest global distribution among sea turtles, found in nearly all oceans.
The Hawksbill sea turtle (Eretmochelys imbricata) is characterized by its pointed, hawk-like beak and its beautifully patterned shell, which has historically been prized in the “tortoiseshell” trade. This species plays a significant role in coral reef ecosystems, as its primary diet consists of sponges. Hawksbills are found in tropical and subtropical waters, often inhabiting coral reefs, where they utilize their narrow beaks to extract food from crevices. They often nest within beach vegetation on secluded beaches.
The Kemp’s Ridley sea turtle (Lepidochelys kempii) is the smallest sea turtle species, typically weighing around 45 kilograms and possessing a round to oval-shaped shell. Its primary habitat is the Gulf of Mexico, with juveniles often found along the eastern coast of the United States. This species is known for its preference for feeding on crabs and other crustaceans found in shallow, coastal waters.
The Olive Ridley sea turtle (Lepidochelys olivacea) is the second smallest sea turtle and is named for its olive-green, heart-shaped carapace. This species is globally abundant and is renowned for its synchronized mass nesting events, known as “arribadas,” where thousands of females come ashore simultaneously to lay eggs. They inhabit warm and tropical waters across the Pacific, Indian, and Atlantic Oceans, frequently found in coastal bays and estuaries.
The Flatback sea turtle (Natator depressus) has a flattened, smooth shell with upturned edges. Unlike other sea turtles, it does not undertake extensive oceanic migrations, remaining primarily in the coastal waters and continental shelf areas of northern Australia, Papua New Guinea, and Indonesia. Its diet is omnivorous, encompassing sea cucumbers, jellies, soft corals, shrimp, and seaweed. Flatback hatchlings are notably larger than those of other species.
Global Conservation Status
The International Union for Conservation of Nature (IUCN) assesses the conservation status of species. The IUCN classifies species based on their extinction risk, using categories like Critically Endangered, Endangered, Vulnerable, and Data Deficient.
The Hawksbill and Kemp’s Ridley sea turtles are both classified as Critically Endangered. Green sea turtles are listed as Endangered. The Loggerhead, Leatherback, and Olive Ridley sea turtles are designated as Vulnerable globally, though many subpopulations within these species are more severely threatened. The Flatback sea turtle is currently listed as Data Deficient by the IUCN, signifying insufficient information to assess its risk, although it is considered Vulnerable under Australian national legislation.
Major Threats to Sea Turtles
Sea turtles confront numerous human-induced threats. Habitat loss represents a major challenge, as coastal development, beach erosion, and artificial lighting disrupt critical nesting sites and foraging grounds. Lights from coastal areas can disorient nesting females and hatchlings, leading them away from the ocean.
Accidental capture in fishing gear is another pervasive threat. Turtles become entangled in nets, longlines, and trawls, leading to injury or drowning. Fishing practices also degrade their food sources and habitats.
Pollution from plastics poses a severe risk to sea turtles. Turtles often mistake plastic bags for jellyfish or ingest plastic, causing internal blockages, starvation, or exposure to harmful chemicals. Entanglement in discarded fishing gear and other marine debris causes injuries, impedes movement, and can result in drowning.
Climate change significantly impacts sea turtles. Rising sand temperatures on nesting beaches can alter the sex ratio of hatchlings, producing more females. Sea-level rise and increased frequency of extreme weather events, such as hurricanes, erode nesting beaches and degrade foraging habitats like coral reefs.
Illegal trade and poaching devastate sea turtle populations. Turtles are still hunted for their meat, eggs, and shells in many regions. This unsustainable harvesting continues to drive population declines.