Sea level rise

Climate change challenges conservation efforts worldwide. Different aspects of climate change are affecting sea turtle populations across the globe. Rising temperatures are an obvious problem for a species with temperature-dependent sex determination. Similar to crocodiles, the incubation temperature of a sea turtle egg determines the sex of the hatchling. The pivotal temperature is close to 29°C: nests that incubate below this temperature produce a majority of males and nests that incubate above it produce a majority of females. Therefore, a warming world would cause a female-bias in sea turtle populations.

Another dangerous aspect of climate change for sea turtles is rising sea levels. A risk of rising sea levels is that turtle nesting beaches will be lost and this could push local turtle populations over the brink unless new suitable nesting beaches are found. A new study that will be published in the December issue of the Journal of Experimental Marine Biology and Ecology looks at the predicted effect of sea level rise on the hatching success of leatherback turtles nesting in Colombia.

The study was conducted on La Playona Beach and looks at the effect of water content of sand on the hatching success of turtle nests. The results of the study show that high sand water content was correlated with reduced hatching success: the wetter a nest, the fewer hatchlings survive from that nest. Projected climate change may therefore be detrimental to the breeding success of sea turtles as nests will have higher exposure to water due to sea level rise and an increase of hurricane events (another predicted consequence of climate change).

Scatterplot showing the relationship between percent sand water content and hatching success (the proportion of eggs that produced live hatchlings that emerged from the nest at the sand surface) in leatherback turtle nests A) in-situ (r = − 0.73, F1,28 = 32.48, P < 0.0001) and B) in experimental clutches in five different sand water content treatments (r = − 0.84, F1,19 = 45.59, P < 0.0001). Black lines shows linear fitted lines. (Source: The Journal of Experimental Marine Biology and Ecology)

The authors of the study conclude that “projected climate change and sea level rise may thus negatively affect leatherback turtle nesting success, although there are several avenues for adaptation to such future change.” They also recommend studying whether or not similar results are found with other species of sea turtles.

Another interesting result of the study is that hatchlings born in wetter nests were smaller in size. They did not appear to have less vigour, though. This last part of the study was measured by “racing” different-sized baby turtles on the beach!

Avoiding predation

A sea turtle’s shell offers great protection to its owner. However, there are predators with razor sharp teeth that are not deterred by the hardness of the carapace and still present themselves as a threat to the sea turtles. The bites are not always deadly, and I have seen more than one turtle with a cookie bite-shaped chunk of its shell missing. The culprit was of course a shark.

An Olive Ridley with a small cookie bite in its shell

An Olive Ridley with a small cookie bite in its shell (above the hind left flipper)

Interesting footage recently published, shows that turtles also have behavioral strategies to avoid predation by sharks.

A first strategy is to roll sideways when a shark attacks. By doing so, the turtle presents the shark with a wide and hard surface that the shark has not angle to attack. Effectively, the turtle is using its shell as a shield that prevents it from fitting into the predator’s mouth.

A second strategy is to swim in tight circles near the shark. The larger body size of the shark does not allow it to turn as sharply and follow the turtle. By doing this, the turtle prevents the shark from closing in on the turtle and catching it. Clever!

Video courtesy of AnimalBytesTV and PRETOMA