The Marine Research Foundation has been conducting studies on juvenile green turtles at Mantanani, off the northwest coast of Borneo since 2006. The reason we have been doing this is because hatchery practices in the region for the last few decades have released a disproportionate number of female hatchlings into the ocean. Sea turtle gender is determined by temperature, and when nests get too warm they produce more females. When shaded, they produce more males. For many years we had nearly entirely female hatchlings reaching the sea, and in 2010 we published a paper in Journal of Herpetology showing how the juvenile population in the wild was heavily female-biased – 93% or so!!! This was not good news….. The animals we were working with were some 10-15 years old, and had about another 10 years to so to reach maturity and return to nest themselves. We were worried that the heavy female-bias was going to result in decreased reproductive success and published the paper as a warning that things were not looking good. Hatcheries in the region now use natural shading by trees or artificial shading with agricultural mesh to cool the nests, and a greater number of male hatchlings are being released to the wild.
In 2011 and early 2012 we didn’t find a single male new recruit (a juvenile just settling into the feeding ground after its first few years’ oceanic phase). But it was with great pleasure that on this recent trip in early August we caught a brand new male juvenile, indicating they are starting to survive and recruit to feeding grounds. The overall ratio is still way off, but this is a positive sign and we hope to find more and more males as the years go by.
This is an interesting case study when one thinks of climate change and a general warming of the world we live in: As temperatures rise will we see a greater proportion of male turtles? How will populations adapt? Our continued studies at Mantanani are aimed at keeping track of this, and we will keep you posted as things develop. In the meantime, congratulations to the hatchery operators in the region who have taken bold and positive steps to balance the natural turtle populations!
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