Sea turtles are ancient marine reptiles that have navigated the world’s oceans for approximately 110 million years. Adapted to life in the sea, they possess streamlined bodies and powerful flippers for extensive migrations. While mostly underwater, they periodically surface to breathe.
From Egg to Hatchling
A sea turtle’s life cycle begins on sandy beaches when a female returns to her natal nesting grounds, typically at night. She uses her front flippers to excavate a body pit, then her hind flippers to dig a vase-shaped egg chamber, often two feet deep. Into this chamber, she deposits a clutch of 50 to 200 spherical, soft-shelled eggs, resembling Ping-Pong balls. A female can lay multiple clutches (four to seven) within one nesting season, with about two weeks between each event.
Eggs incubate in warm sand for 45 to 70 days, influenced by species and local conditions. Temperature-Dependent Sex Determination (TSD) dictates hatchling sex. Warmer sand temperatures, generally above 31°C, produce predominantly female turtles, while cooler temperatures below 27.7°C result in more males. Temperatures fluctuating between these extremes yield a mixed-sex clutch.
Upon hatching, tiny turtles, equipped with a temporary egg tooth (“caruncle”), collectively break free from their shells. They then work together to dig to the sand’s surface, often emerging in a synchronized “turtle boil.” This emergence usually occurs at night, and the hatchlings instinctively scramble towards the brightest horizon, typically the reflection of the moon or stars on the ocean surface. This journey to the sea, known as the “frenzy period,” exposes them to predators like birds, crabs, and land mammals.
The Ocean’s Apprenticeship: Juvenile Stages
After entering the ocean, hatchlings embark on a phase often called the “lost years.” During this period, which can last from several months to a decade depending on the species, young sea turtles are largely unobserved by humans. Major ocean currents, like the Gulf Stream, carry them to offshore foraging grounds such as the Sargasso Sea, which provide shelter and food.
Early assumptions suggested passive drift, but recent research using satellite tags indicates juvenile sea turtles actively swim and move between open ocean and shallower continental shelf waters. Their diet typically consists of plankton, jellyfish, and other small marine organisms. Juvenile green turtles, while omnivorous, gradually shift towards a more herbivorous diet as they grow.
The “lost years” are a time of growth and development. Turtles rapidly increase in size, providing better protection against predators. This growth prepares them for eventual return to coastal waters, where they mature.
Reaching Adulthood and Reproduction
After years in the open ocean, juvenile sea turtles transition into adulthood and begin reproduction. Sexual maturity varies among species, from 7 to 50 years. For example, leatherback sea turtles can mature as early as 7-13 years, while green sea turtles may take 26-40 years. This maturation often coincides with their return to coastal habitats.
Adult turtles undertake extensive migrations, often thousands of miles, to reach breeding sites. Mating occurs in the water near these nesting areas, typically several weeks before the nesting season begins. Male sea turtles use specialized claws on their front flippers to grasp the female’s shell during copulation. Females may mate with multiple males, a behavior that contributes to the genetic diversity of their offspring.
Following mating, female turtles exhibit fidelity to their natal beach to lay eggs. Most species nest at night, with the female digging her nest, depositing her clutch, and covering and camouflaging the site before returning to the sea. Females typically engage in multi-clutch nesting, laying several nests within a season, and generally nest every two to four years.
Lifelong Journey: Adult Life and Migration
Adult sea turtles are known for their longevity, with many species living for several decades. While the exact lifespan is difficult to determine in the wild, scientists estimate they can live 60 years or more, with some potentially reaching a century. These long-lived creatures undertake extensive migratory journeys between their feeding grounds and nesting beaches.
Their ability to navigate these vast oceanic distances relies on a combination of environmental cues. Sea turtles utilize the Earth’s magnetic field as a form of internal compass and map (geomagnetic imprinting) to guide their long migrations and return to specific locations. They also use wave direction, and potentially solar and olfactory cues, to orient themselves.
The diet of adult sea turtles varies by species. Green sea turtles are primarily herbivores, grazing on seagrass and algae, while loggerheads are carnivores that feed on crustaceans like crabs and conchs. Leatherback turtles specialize in a diet of jellyfish, and hawksbills predominantly consume sponges. These diverse feeding habits play a role in maintaining the health and balance of marine ecosystems. Green turtles help keep seagrass beds healthy, and hawksbills control sponge populations on coral reefs. After nesting, females return to feeding grounds to replenish energy reserves.