The biggest sea turtle in the world is the Leatherback Sea Turtle (Dermochelys coriacea). This colossal ocean wanderer is the largest of all turtle species and the heaviest non-crocodilian reptile alive today. The Leatherback is the sole surviving member of its taxonomic family, setting it apart from its hard-shelled relatives.
Defining the Largest Sea Turtle
The Leatherback Sea Turtle earns its name as the largest by sheer scale, both in length and mass. Adults commonly measure between 1.2 and 1.8 meters (4 to 6 feet) in curved carapace length, typically weighing 295 to 907 kilograms (650 to 2,000 pounds). These averages already eclipse the maximum size of most other sea turtle species. The largest confirmed specimen was a male found in Wales, weighing 961.1 kilograms (2,120 pounds) and measuring 2.91 meters (9 feet, 6 inches) in total length. This extreme size is a testament to the Leatherback’s rapid growth rate, which aids in survival across diverse environments.
Unique Anatomy and Adaptations
The biological structures that permit the Leatherback to attain massive dimensions are unique among sea turtles. Its most distinguishing feature is its carapace, which lacks the bony plates, or scutes, found on all other species. Instead, the shell is composed of a mosaic of thousands of small, interlocking bony plates called osteoderms. These osteoderms are embedded within a thick layer of rubbery, oil-saturated connective tissue and skin.
This unique, flexible carapace structure is an adaptation that allows the Leatherback to withstand the crushing pressure of deep-sea environments. These turtles are among the deepest-diving marine animals, regularly descending to depths greater than 1,000 meters (3,281 feet) in search of prey. The pliable shell permits compression without fracturing, a capability hard-shelled species lack.
The Leatherback also possesses an unusual thermoregulatory adaptation known as gigantothermy, a heat retention strategy aided by its large body size. By having a low surface area-to-volume ratio, a thick layer of insulating fat, and a specialized counter-current heat exchange system, the turtle maintains a core body temperature warmer than the surrounding water. This ability allows them to migrate and forage in cold, temperate waters, including areas as far north as Alaska and as far south as the Arctic Circle.
Comparing Size to Other Species
The size of the Leatherback is apparent when compared to other sea turtles. The largest hard-shelled species is the Loggerhead Sea Turtle (Caretta caretta), which can reach a maximum weight of about 545 kilograms (1,202 pounds). However, the average adult Loggerhead usually weighs between 82 and 200 kilograms (180 to 440 pounds). The Green Sea Turtle (Chelonia mydas) is the third-largest species, with the largest individuals weighing up to 500 kilograms (1,102 pounds). The largest Leatherbacks can weigh three to four times more than the largest Green turtles, highlighting their solitary position at the top of the size hierarchy.
Conservation Status
Despite its impressive size and wide distribution, the Leatherback Sea Turtle faces significant threats to its survival. Globally, the species is classified as Vulnerable by the International Union for Conservation of Nature (IUCN). However, this global status masks the dire situation of several distinct populations, such as those in the Pacific and Southwest Atlantic, which are listed as Critically Endangered. A major threat is accidental capture in commercial fishing gear (bycatch), which accounts for significant mortality due to the Leatherback’s extensive migratory routes. Their diet of soft-bodied invertebrates like jellyfish also puts them at risk of plastic ingestion, as discarded plastic bags are often mistaken for food.