Global Warming Linked to Shift in Sea Turtle Gender Ratio in the Mediterranean

Turkish scientists have discovered a connection between climate change and the gender balance of sea turtles in the Mediterranean. Due to global warming, the temperature of nests on beaches is rising, resulting in an increased proportion of female turtles.

This conclusion was drawn by a member of the board at the Turkish Center for Research on Sea Turtles, Rescue, and Rehabilitation (DEKAMER), and a professor at the Faculty of Veterinary Medicine at Pamukkale University, Doğan Sözbilen.

According to the scientist, the gender of sea turtles in the Mediterranean depends on temperature, with rising temperatures adversely affecting their well-being.

“When they lay eggs in the sand, the gender of the offspring is not determined by genetics but by the environment. When the nest temperature on the beach reaches 29 degrees Celsius, half of the offspring in the nest are females, and the other half are males. If temperatures exceed this value, the number of females increases, while temperatures below this threshold result in more males. Moreover, when temperatures reach 33-34 degrees Celsius, embryo mortality begins,” explained the expert.

Therefore, due to rising temperatures, sea turtles are seeking cooler habitats for reproduction and breeding during cooler periods.

Along the Mediterranean coast of Turkey, species such as caretta caretta (loggerhead sea turtle) and chelonia mydas (green sea turtle) nest.

The researcher noted that these turtles reach adulthood 20–25 years after birth, and females return to the beach where they were born to lay eggs.

“The countries with the highest number of caretta caretta nests in the Mediterranean are Turkey and Greece. Nearly 80% of green sea turtle nesting occurs in Turkey, where there are more than 5,000 such nests. Green sea turtles have more than 2,000 nests,” added the specialist.

According to experts' estimates, over the past 10 years, the number of nests has increased by 50%. Currently, there are approximately 7,000 to 8,000 adult female caretta caretta turtles and about 2,000 adult female green sea turtles throughout the Mediterranean.

Due to the increase in their population in the Mediterranean, sea turtles were removed from the “endangered species” list on the International Union for Conservation of Nature (IUCN) Red List in 2015.

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