Sea Turtle Population Boom May Mask Looming Collapse, Study Warns

UK - Ekhbary News Agency

Sea Turtle Population Boom May Mask Looming Collapse, Study Warns

Around the globe, conservationists have often celebrated what appear to be significant increases in sea turtle populations. In Cape Verde, West Africa, for instance, loggerhead turtle nests have surged to 100 times the numbers recorded in 2008. However, scientists are now issuing a stark warning: this apparent success story might be masking an impending population collapse, driven by the insidious effects of climate change.

New research from Queen Mary University of London, utilizing drone surveys and 15 years of nesting data, suggests that booming nest counts could be profoundly misleading. The core issue lies in the impact of rising global temperatures on sea turtle reproduction. As ambient temperatures increase, a disproportionately higher number of sea turtle eggs are developing into females. This environmental shift, often referred to as temperature-dependent sex determination (TSD), poses a severe threat to the genetic diversity and reproductive capacity of these ancient marine reptiles.

The findings, which have been posted to the preprint server bioRxiv.org and are awaiting peer review, highlight a critical imbalance. "We think that there’s a bit of a mirage," stated Christophe Eizaguirre, a conservation geneticist at Queen Mary University. While acknowledging the vital role of conservation efforts such as marine protected areas, fishing regulations, and nest protection, Eizaguirre emphasized that these measures may not fully address the emergent threat of sex ratio distortion.

Similar to other reptiles like crocodiles, the sex of sea turtle hatchlings is determined by the incubation temperature of their eggs. Warmer sand temperatures predominantly produce females, while cooler conditions favor the development of males. Jeanette Wyneken, a biologist at Florida Atlantic University who was not involved in the study, colorfully described this phenomenon: "The way we describe it in my lab is ‘hot chicks and cool dudes’."

The research team employed drones to survey and photograph the breeding population, discovering a striking 9-to-1 ratio of females to males. Biologist Fitra Arya Dwi Nugraha, also from Queen Mary University, explained how the sex of adult turtles could be identified: "We can differentiate between females and males by the tails. Males have longer and thicker tails." This observed ratio is far from the roughly even split considered ideal, which is believed to occur at incubation temperatures around 29 degrees Celsius.

The study's authors hypothesize that the inflated number of female loggerheads (Caretta caretta) contributing to nesting inflates the nest count, creating a deceptive picture of population health. Without a sufficient number of males to ensure successful breeding, the population's growth could rapidly reverse, though predicting the precise tipping point remains challenging.

Dr. Wyneken, while recognizing the study's contribution, raised concerns regarding its methodology for determining the sex ratio. She pointed out that while adult males are identifiable by drone, distinguishing the sex of subadult individuals, which can be similar in size to females, is more difficult. "It’s possible that they are counting some immature males as females," she noted, suggesting that the 9-to-1 ratio might be even more skewed if such errors are present. Wyneken advocates for more invasive methods, such as laparoscopy surgery on hatchlings, for a more accurate sex determination.

Dr. Eizaguirre responded that hatchlings typically only return to their natal beaches, like those in Cape Verde, once they reach sexual maturity, implying that the drone surveys were capturing reproductively active individuals.

Sea turtles possess natural adaptive strategies to mitigate a female bias. Males can mate more frequently, females can store sperm to fertilize multiple clutches, and both sexes often engage in multiple partnerships. Additionally, conservation programs sometimes involve relocating eggs to protected hatcheries to safeguard them from predators, poachers, and adverse environmental conditions. However, as Wyneken cautioned, "If something goes wrong, ‘you’re putting all your eggs in one basket.’"

The consensus among scientists is that a significant global skew towards females is a serious concern. "You expect more females," Wyneken conceded, but she questioned the sustainability of "seasons where we get 100 percent female, again and again and again, or 98 percent female? That’s not sustainable." Such dramatically skewed sex ratios are already being observed in warmer regions, including beaches along the northern Great Barrier Reef.

The researchers hope their findings will serve as a crucial reminder against complacency in conservation efforts. "We really don’t want is the effort to stop," Eizaguirre stressed. He added that ongoing, adaptive conservation strategies are paramount to provide sea turtle populations with the time needed to adjust to their changing environment. The study underscores the need for continued vigilance and evolving conservation approaches to ensure the long-term survival of these vulnerable species.

Ekhbary News Agency