The leatherback sea turtle, Dermochelys coriacea, is the largest sea turtle species and the sole surviving member of its taxonomic family. Unlike other sea turtles, it lacks a hard, bony shell. Instead, its carapace is covered by thick, pliable, leathery skin stretched over a mosaic of small, interlocking bones called osteoderms. This unique, flexible structure allows the turtle, which can weigh over 1,500 pounds, to withstand extreme hydrostatic pressures at great depths. The leatherback regularly dives past 1,000 meters in search of prey, defining a life cycle that spans entire ocean basins.
Nesting Locations and Hatching
The life cycle begins when the female returns to a tropical or subtropical beach to nest, often exhibiting natal homing behavior to the region where she was born. Key nesting sites are distributed globally, including beaches in Trinidad, Costa Rica, French Guiana, and Indonesia. A female typically nests multiple times within a single season, laying between four and seven clutches, with a two- to four-year interval between nesting seasons.
Each nest contains 50 to 90 yolked eggs, along with a layer of smaller, yolkless eggs laid on top. The temperature of the sand during the middle third of the incubation period determines the sex of the hatchlings, known as Temperature-Dependent Sex Determination. Warmer temperatures, generally above 29.5 degrees Celsius, tend to produce females, while cooler temperatures produce males.
The incubation period lasts approximately 60 days. Hatchlings emerge at night and make a mass exodus toward the ocean. This initial journey is perilous, and only a fraction successfully reaches the water. The overall hatching success rate is relatively low compared to other sea turtles, sometimes averaging 30 to 60 percent.
The Journey to Adulthood
Once hatchlings enter the ocean, they begin the “Lost Years,” a pelagic stage where data on their movements and distribution is limited. Researchers are developing micro-satellite tags small enough for juveniles, which are beginning to reveal details about this phase.
Young leatherbacks must grow extremely quickly to survive the high mortality risks of the open ocean; less than one in a thousand hatchlings is estimated to survive to adulthood. Juveniles can reach a curved carapace length of 75 centimeters in roughly three years. During this time, they remain in warmer, tropical, and subtropical waters, often carried by major ocean currents.
The juveniles are primarily oceanic, spending their time in the open water column as they mature. This rapid growth rate is thought to be an adaptation allowing them to quickly outgrow the size range of most oceanic predators. The juvenile phase concludes when the turtle reaches sexual maturity, a time frame still under scientific investigation.
Oceanic Feeding and Physiology
The adult leatherback is a specialized marine predator whose diet consists almost exclusively of soft-bodied invertebrates, such as jellyfish, salps, and siphonophores. To facilitate this diet, the turtle possesses a unique throat structure lined with backward-pointing keratinous spines, called papillae. These spines prevent slippery prey from escaping and help expel excess seawater.
The leatherback has adaptations allowing it to forage in frigid waters, distinguishing it from other reptiles. This includes gigantothermy, where the turtle’s large body mass, thick subcutaneous fat, and specialized circulatory systems retain metabolically generated heat. A countercurrent heat exchange system in the flippers and core body helps maintain a core temperature up to 18 degrees Celsius warmer than the surrounding water.
This internal temperature regulation is coupled with the turtle’s deep-diving capacity. Leatherbacks routinely dive to depths exceeding 1,000 meters to follow their prey, with recorded dives reaching over 1,344 meters. Physiological mechanisms like collapsible lungs allow them to manage immense pressure changes and avoid decompression sickness during these dives.
Long-Distance Travel Routes
The adult life of the leatherback is characterized by long-distance movements between tropical nesting grounds and cold, rich foraging areas. This bipolar migration pattern involves covering distances often exceeding 10,000 miles annually. Atlantic populations, for example, migrate from Caribbean nesting beaches north toward feeding grounds off the coast of Canada.
Eastern Pacific leatherbacks undertake one of the longest migrations, traveling from nesting sites in Costa Rica southwest into the South Pacific Gyre. Although ocean currents play a role in dispersal, the turtles actively compensate for current drift, demonstrating sophisticated navigation skills.
Leatherbacks are believed to use the Earth’s magnetic field as a form of global map, relying on geomagnetic navigation to orient themselves across the open ocean. This ability, combined with cues from ocean currents and water chemistry, allows them to return with precision to the same nesting regions every few years.
The Importance of Conservation Efforts
Leatherbacks face threats throughout their life cycle, leading to population declines in many regions.
Threats on Nesting Beaches
Coastal development and rising sea levels reduce available habitat. Climate change-driven increases in sand temperature skew hatchling sex ratios, potentially leading to a lack of males. Poaching of eggs for consumption also occurs in some areas.
Threats in the Marine Environment
The primary threat is incidental capture, or bycatch, in commercial fishing gear, such as longlines and driftnets, where the turtles drown. Plastic pollution is also a hazard, as turtles frequently mistake floating plastic bags for jellyfish, leading to fatal digestive blockages.
Conservation requires international collaboration due to the species’ highly migratory nature, crossing many national jurisdictions. Efforts focus on:
- Protecting nesting beaches through patrols and nest relocation.
- Implementing turtle-safe fishing gear and time-area closures for fisheries.
- Reducing plastic waste in the ocean.
These actions are necessary to ensure the species’ survival.