‌Previous research has suggested that there are more female sea turtles at important colonies, known as rookeries, and this is linked to warmer incubation temperatures.  This has heightened concerns for the long-term conservation of sea turtles in a warming world and has led to researchers measuring temperatures at nesting beaches around the world to better understand the male-to-female ratio that these rookeries are producing.

A new study by Swansea University, Deakin University and University of Florida academics, published in the journal Scientific Reports, looked at the impact of warming temperature on two populations of sea turtles nesting in Diego Garcia in the Chagos Archipelago, British Indian Ocean Territory (BIOT).

The researchers recorded the sand temperature using small temperature loggers buried at turtle nesting depths on Diego Garcia between 2012 and 2014. Loggers were placed in the different nesting beach areas where hawksbill and green sea turtles nest. The results of the study showed that incubation temperatures are relatively cool, with a mean temperature range of 28.1-29.1 °C during Austral Summer and dropping to 26.9-27.5 °C during Austral Winter. The researchers estimated that the Diego Garcia hatchlings sex ratios were 53% and 63% male hatchlings for hawksbill and green turtles.  

The beaches of Diego Garcia have characteristics that maintain cool nest temperatures including:-

• intact natural vegetation providing heavy shade
• heavy rainfall
• narrow beach platforms ensuring sea turtles nest close to the sea.

These results contrast with the predominantly high female skew reported for turtle hatchlings at most rookeries around the globe and highlights how local beach characteristics can drive incubation temperatures.

The evidence suggests that sites that have heavy shade associated with intact natural vegetation are likely to provide conditions suitable for male hatchling production in a warming world. The Chagos Archipelago is likely to be a source of male turtles to balance sea turtle populations in the Indian Ocean.

Nicole Esteban, one of the authors of the article (pictured), said: “The findings of our study provide positive news for sea turtles in the Western Indian Ocean; unlike other rookeries producing mainly female hatchlings, the beaches of the Chagos Archipelago are densely vegetated and the cooling effect of the vegetation produces a balance of males and females. This highlights that conservation managers need to maintain the natural beach vegetation for successful conservation of sea turtles.“

Read the research “Male hatchling production in sea turtles from one of the world’s largest marine protected areas, the Chagos Archipelago” published by Scientific Reports (2016).