Conservationists worldwide are celebrating apparent recoveries in sea turtle populations, with some regions showing dramatic increases in nesting activity. For example, Cape Verde has seen a 100-fold rise in loggerhead turtle nests since 2008. However, new research suggests this growth may be masking a critical, and potentially irreversible, decline: a severe imbalance in sex ratios due to climate change.
Scientists at Queen Mary University of London warn that rising global temperatures are skewing hatchling sex ratios towards overwhelmingly female populations. Sea turtles, like many reptiles, determine sex via incubation temperature; warmer sand produces females, while cooler conditions yield males. This isn’t just about future breeding potential; it’s about the sustainability of entire populations. The study, currently posted on bioRxiv.org pending peer review, used 15 years of nesting data and drone surveys to reveal a concerning trend.
The researchers discovered breeding populations with ratios as extreme as 9 females to every 1 male. Using drone imagery to identify males by their thicker, longer tails, they hypothesize that inflated nest counts give a false sense of health. Without sufficient males, even a seemingly thriving population faces inevitable collapse. “We think that there’s a bit of a mirage,” says researcher Christophe Eizaguirre.
Why This Matters: The imbalance isn’t just a theoretical concern. Turtle populations have evolutionary mechanisms to cope with some female bias (such as sperm storage and multiple mating), but extreme skews are unsustainable. Regions like the northern Great Barrier Reef are already showing near-total female hatchling seasons, signaling an immediate threat. Conservation efforts, while helpful, may be ineffective if the underlying temperature issue isn’t addressed.
Some scientists raise concerns about the accuracy of drone-based sex identification, particularly with subadult turtles. However, the core message remains clear: conservation successes must be reevaluated in light of climate-driven sex ratio distortions. Relocating eggs to hatcheries, while intended to boost survival, carries risks if the fundamental problem of imbalanced sex ratios is ignored.
The researchers emphasize that conservation efforts cannot slow down. The goal isn’t just to protect nests, but to buy time for populations to adapt. Without ongoing, adaptive measures, the hard-won gains of recent years may vanish, leaving sea turtle species facing a silent, yet catastrophic, decline.
