Terrestrial basking

Turtles usually only come ashore to nest. It is rare to see a marine turtle on land otherwise. But it does happen: at certain beaches turtles come ashore to bask in the sun during the day. The only species known to exhibit this unique behaviour is the green turtle. It regularly comes to bask on the beaches of Hawai’i, and there have also been reports of turtles basking in the Galápagos Archipelago and in Western Australia. While basking the turtles will seemingly close their eyes and fall asleep. This creates the unique situation for beach goers to have to share the beach with napping turtles!

The obvious benefit of basking for reptiles is thermoregulation: raising body temperature accelerates metabolic processes like digestion and growth. Being cold-blooded, this is probably the main reason why these green turtle bask and nap on land. A possible added benefit of being on land is the reduction in exposure to marine predators such as tiger sharks. Finally, it could be that staying on land is also more energy-efficient as the turtle does not have to periodically swim to the surface for air. There are turtles that seem to prefer to bask at the same spot every day. On some beaches, tape is placed around the turtles’ favourite sleeping spots to ensure the turtles can rest undisturbed. It is also reported that certain groups of turtles always bask together, like friends. Occasionally Hawaiian monk seals also join the turtles for their nap, like in the pictures below!

This slideshow requires JavaScript.

A big thank you to Mark Sullivan for all the great pictures of the turtles with the seals. Check out his great work with Hawaiian monk seal! I also thank Rebecca Scott for the original post idea.

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