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Climate change could have a drastic effect on sea turtles - threatening their long-term survival - in a way that would surprise most people.
The raised temperature of the sand where the turtle eggs are laid could see turtle populations become solely female.
Sea turtles are unusual in that the sex of hatchlings is determined, not by sex chromosomes (as is the case with humans and other mammals), but, rather, by the incubation temperature - a phenomenon known as temperature-dependent sex determination.
Above a pivotal incubation temperature, typically near 29°C, the majority of sea turtle eggs produce female hatchlings and vice versa. So, warming temperatures, occurring as part of global climate change, may cause the feminisation of sea turtle populations.
While this threat of feminisation has been known for many years, there have been few attempts to predict how the sex ratio of populations may change in the future and the resulting extinction risk.
Now, in a study just published in Nature Climate Change, estimates of past, present and future sex ratios have been made for one of the world’s largest sea turtle rookeries, the Cape Verde Islands in the Atlantic, where large numbers of loggerhead turtles breed.
An international team from Deakin’s School of Life and Environmental Sciences and Centre for Integrative Ecology, Swansea University (UK) and the NGO SOS Tartarugas (Cape Verde Islands), has recorded sand temperatures on nesting beaches over several years using small data-loggers. These sand records were then combined with past measurements of environmental conditions on the islands since 1850, and compared with climate predictions for the next 100 years made by the Intergovernmental Panel on Climate Change (IPCC).
Deakin’s Chair in Marine Science, Professor Graeme Hays, explained that this process allowed researchers to derive a robust 250-year time-series of incubation temperatures, hatchling sex ratios, and adult breeding sex ratios.
“This study made a conceptual advance by predicting the impact of climate warming across male-female breeding ratios and nesting numbers,” Professor Hays said. “It provides us with a holistic approach to assessing and addressing the conservation of sea turtles.”
“In one way, the outcomes of this work are good news,” he added. “Despite predicted warming and increasingly female skewed sex ratios, entire feminisation of the population is not imminent in the next few decades. In fact, warm incubation temperatures may have the unexpected conservation benefit of increasing the number of breeding females and, hence, the total size of the population.”
“However, while the turtle population size should be secure for the next 150 years, researchers will need to monitor populations and determine the minimum number of males needed for the species to survive.”
“This monitoring will be central to the conservation of the various sea turtle species, and will indicate when intervention may be required, such as moving nests to cooler beaches or planting trees to shade nest areas.”
Read the full article, "Effects of rising temperature on the viability of an important sea turtle rookery" from Nature Climate Change.