Leatherback sea turtles, a lineage over 100 million years old, are the largest living turtles, reaching up to 2.7 meters (8.9 feet) and weighing over 500 kilograms (1,100 pounds). Unlike other sea turtles, leatherbacks have a flexible, leathery shell instead of a hard carapace, allowing dives over 1,000 feet. They inhabit a global range from tropical to subpolar waters, but many subpopulations are critically endangered.
Temperature-Dependent Sex Determination
Leatherback sea turtle hatchling sex is determined by sand temperature during incubation, known as Temperature-Dependent Sex Determination (TSD). This occurs during the middle third of incubation, the “temperature-sensitive period” (TSP). During this window, temperature cues influence sex hormone production, guiding ovary or testes development.
Cooler incubation temperatures produce male hatchlings, while warmer temperatures yield females. A “pivotal temperature” produces an equal male-to-female ratio. For many sea turtle species, including leatherbacks, this is around 29°C (84.2°F), though it varies. Below 27.7°C (81.86°F) produces males, while above 31°C (87.8°F) yields all females.
Warming Nesting Beaches
Rising global temperatures affect nesting beaches where leatherback sea turtles lay eggs. As temperatures increase, sand becomes warmer, pushing incubation environments above the pivotal temperature. This warming results in more nests producing disproportionately female hatchlings. Some nesting sites have seen extreme female-biased ratios, with certain green sea turtle populations showing nearly 99% female hatchlings.
Even a half-degree Celsius shift can significantly skew a nest’s sex ratio. Too-high temperatures can also increase embryo mortality, reducing hatching success and reproductive output. Urban development near nesting beaches exacerbates this, as buildings and roads absorb and reflect heat, further raising sand temperatures.
Consequences of Imbalanced Sex Ratios
A highly skewed, predominantly female sex ratio concerns leatherback sea turtle populations. While a slight female bias might seem beneficial, an extreme imbalance can lead to a male shortage. This can result in mate-finding difficulties, as there may not be enough to fertilize all available females. This scenario can reduce reproductive success and lead to a decline in genetic diversity.
For long-lived species like leatherbacks, skewed hatchling sex ratio effects may not be apparent for decades, as turtles take 25 to 40 years to reach sexual maturity. If female-biased hatchlings continue unchecked, it could create a reproductive bottleneck, threatening population survival.
Protecting Future Generations
Addressing temperature-dependent sex determination challenges in a warming world requires conservation approaches. One strategy is relocating nests to cooler beach sections or specialized hatcheries. Relocation must occur within 12 hours of laying to minimize harm to developing embryos. Another method is shading nests with natural materials like palm fronds or artificial structures to reduce sand temperatures. Studies show shading can reduce incubation temperatures, increasing male hatchling production and improving hatchling performance.
Researchers explore other techniques, such as irrigating nests to cool sand. Beyond direct intervention, understanding TSD genetics and how sea turtles might adapt naturally, like shifting nesting times to cooler periods, is ongoing research. These steps are essential for safeguarding leatherback populations against changing sex ratios and ensuring their long-term survival.