Drones and sea turtle research

Unmanned Aerial Vehicles (UAVs – drones) are increasingly employed to monitor and protect wildlife. The new technology has proven to be particularly useful to survey species and habitats that are difficult to access. In sea turtle research drones are being used for various purposes. In Australia conservationists use them to count turtles at Raine Island, the world’s largest green sea turtle nesting site, and map the island’s topography. In Suriname the World Wide Fund for Nature (WWF) uses drones to survey beaches and collect evidence of the illegal poaching of turtle eggs.

Drones can also be used to answer questions about turtles’ lives in the oceans. A new study published recently in Herpetological Review  deployed UAVs to observe the behaviour of green sea turtles off the coast of Mexico. One of the benefits of using this technology is that there is little risk of disturbing the animals that are being observed. The study revealed interesting footage of the courtship and mating behaviours of turtles at sea. The authors of the study conclude that “UAV technology is useful for not only enhancing our understanding of sea turtle behaviors in the natural environment, but also in identifying the location of critical habitat for important life-history events, such as courtship and mating.” One of the other benefits is that drones will show a unique bird’s-eye view of turtles returning to the water after nesting!

Video courtesy of The Leatherback Trust

Turtle-cams

A turtle’s underwater life has long been a mystery for science. Modern equipment such as GPS loggers give a lot of interesting insight into the turtle’s life, but there are things that GPS loggers simply cannot register. To learn more about the behaviour of turtles on a fine spatio-temporal scale, scientists resort to different technologies.

In 2005 Dr Richard Reina from Monash University collaborated with National Geographic to study the behaviour of female leatherbacks during their nesting season. The researchers attached video cameras to the carapace of female leatherbacks using suction caps. The cameras were automatically released from the turtle after several hours and the researchers then relocated the devices using a VHF transmitter. The footage presented an interesting view of underwater life from a turtle’s perspective and provided new insight into the private life of leatherbacks:

  • The video showed that the females turtles did not feed during the nesting season (which can span several months!).
  • The footage also exposed the aggressive and harassing behaviour of males wanting to pair with the females. Some males would repeatedly strike and bite the females. Others would even try to prevent the females from returning to the surface.
  • The video also revealed that some females seemed to actively avoid the males.

The results of this study were published in the Journal of Experimental Marine Biology and Ecology.

Using the turtle-borne camera has therefore given the researchers a great perspective on what the turtles do in their natural environment. New research published last month in Frontiers in Ecology and Evolution studied the feeding behaviour of leatherbacks off the coast of Nova Scotia. In the following video you can see a leatherback looking for its favourite meal!

Video courtesy of the Canadian Sea Turtle Network

Terrestrial basking and climate change

Terrestrial basking is a rare behavior observed in populations of green sea turtles in Hawai’i, Western Australia, and the Galápagos Archipelago. Being cold-blooded, the main reason why turtles bask on land is probably to regulate their body temperature but scientists speculate that terrestrial basking may also aid immune function, predator avoidance, and may even prevent unwanted courtship.

New research published in Biology Letters examined the relationship between terrestrial basking and climate. Having counted the number of turtles that bask on one Hawaiian beach every day for six years, the researchers found that terrestrial basking peaks in the year when the sea surface temperatures are lowest. Terrestrial basking generally happens when sea surface temperatures fall below 23°C. This suggests that terrestrial basking is a response to seasonally cool ocean temperatures.

Picture 2

Basking varies seasonally in concert with cool SST. Green circles are standardized anomalies of the number of turtles observed basking weekly at Laniakea, Oahu. Blue circles are weekly AVHRR SST data for this location. Thick dark lines are the Fourier series for each timeseries. (Source: Biology Letters)

However, since the sea surface temperatures at the sites where turtles bask on land is warming on average 0.04°C per year, the researchers predict that in the future the waters will be warm enough that the turtles will no longer come on land for warmth. The researchers estimate terrestrial basking may cease in Hawaii by 2039, in Australia by 2086, and in the Galápagos by 2102. Since other populations of marine turtles are successful without having to resort to terrestrial basking, this will probably not have drastic negative impacts on these green turtle population, but this does mean that beach goers of the future will not have the privilege of sharing the beach with napping turtles.

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!

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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