Five sea turtle species nest on these beaches with peak seasons varying by species. Climate change is shifting nesting dates, with potential mismatches to hatchling food availability.
A convergence of ancient mariners
The southern coast of Sri Lanka, particularly the 2-kilometer stretch of sand at Rekawa Beach near Tangalle, is an important nesting ground for five of the world's seven sea turtle species. This convergence makes the area unusually important for marine biodiversity. The most frequent visitor is the Green turtle (Chelonia mydas), joined by the Olive Ridley (Lepidochelys olivacea), Loggerhead (Caretta caretta), Hawksbill (Eretmochelys imbricata), and the massive, rare Leatherback (Dermochelys coriacea).
Each species follows its own ancient schedule. The peak nesting season for Green turtles runs from about February to April, while Olive Ridleys prefer November through March. Overall, nesting activity is highest between April and July, when 5 to 15 turtles might come ashore on a given night. Females of most species lay clutches of 100 to 140 eggs, which incubate in the sand for approximately 45 to 70 days. The largest species, the Leatherback, can weigh over 900 kilograms and undertakes migrations of more than 10,000 miles. Its diet consists almost exclusively of soft-bodied jellyfish and salps. By contrast, the much smaller Hawksbill turtle has a narrow, bird-like beak for extracting sponges from crevices in coral reefs.
A schedule under thermal threat
The timing of these natural cycles, known as phenology, is under pressure from climate change. Sea turtles exhibit temperature-dependent sex determination (TSD), meaning the temperature of the sand during a critical period of incubation determines the sex of the hatchlings. For many species, incubation temperatures above 31°C (87.8°F) produce almost all females, while temperatures below 27.7°C (81.8°F) result in mostly males. The important temperature, which yields a balanced sex ratio, is around 29°C (84.2°F).
Increasing global temperatures are warming the sands of Tangalle's beaches, which skews the hatchling sex ratio heavily towards females. Studies of green turtle populations in other warming regions have found that hatchlings from some beaches are already over 99% female. This "feminization" of the population presents a long-term threat to genetic diversity and reproductive viability. Warmer sand also accelerates embryo development, leading to shorter incubation periods and smaller hatchlings. A shift in the timing of hatching can also create a dangerous mismatch with the peak availability of plankton and other food sources in the ocean, reducing the already low survival rates for young turtles. Local conservation groups, like the Rekawa Turtle Watch, actively monitor the beaches, protecting nests from poaching and other threats, and providing an ethical way for visitors to witness this natural event.
💡Fun Facts
The Leatherback sea turtle is the world's largest turtle and can dive to depths of nearly 1,200 meters (4,000 feet), deeper than most marine mammals.
The temperature of the sand during the middle third of incubation determines the sex of sea turtle embryos.
The Green turtle is named for the color of its body fat, not its shell, which results from its herbivorous diet of seagrass and algae.
A Leatherback's throat is lined with backward-pointing spines to help it swallow slippery prey like jellyfish.
Guided night watches with conservation groups like Rekawa Turtle Watch typically run from 8:30 PM until late, as nesting is a nocturnal activity.
Admission
There is generally a fee for guided conservation walks, with proceeds supporting local nest protectors. Donations are encouraged.
Accessibility
The terrain is a natural, sandy beach, often with sloped sections. Movement occurs in darkness, requiring careful walking. It is not wheelchair accessible.