Female-biased sea turtle populations

The temperature at which a sea turtle egg incubates determines the sex of the hatchling. Below a pivotal incubation temperature of about 29.0°C the majority of individuals are born male and above that temperature the majority of individuals are born female. This unique process, known as Temperature-Dependent Sex Determination (TSD), is widespread among reptiles.

What will happen to sea turtle populations when air temperatures rise due to climate change? This is a central question of my latest research, the results of which were published in the Journal of Experimental Marine Biology and Ecology this week.

The study was a collaboration between researchers from Swansea University (United Kingdom) and Deakin University (Australia), and conservationists working on the Dutch Caribbean island of Saint Eustatius. We recorded sand temperatures at a turtle nesting beach where leatherbacks, hawksbill and green sea turtles nest. These data were combined  with temperature projections from the Intergovernmental Panel on Climate Change (IPCC) to model how sand temperatures will change in the next 100 years.

The results showed that sand temperatures are relatively high (ranging from 29.1-33.3°C) at this nesting site and that all three species of sea turtles are female-biased: we estimate that for the current populations of hawksbill, leatherback and green turtles the percentage of turtles born male are 36%, 24%, and 16%, respectively. Projecting into the future, it is likely that the female-skew will be intensified due to warming air temperatures. For example, projections indicate that only 2.4% of green turtle hatchlings will be males by 2030, 1.0% by 2060, and 0.4% by 2090.

Nicole Esteban, a Swansea University researcher and former St Eustatius National Parks (STENAPA) manager, who is a lead author of the paper says that “there is a real concern that there will not be enough males born on Saint Eustatius in the future. If there are too few males, the local population is at risk of collapsing. Another concern is that turtle eggs do not develop above a certain temperature. The study highlights the extinction risks of climate change to species whose biology is closely linked to temperature.”

This research underlines that there is real need for effective conservation measures to be put in place to prevent the localised extinction of these turtle populations. Potential conservation strategies include shading turtle nests on the beach or moving nests to a cooler section of a beach such as a protected hatchery.

fdfa http://www.frogfishphotography.com/index.html

A hawksbill turtle swimming near a wreck in Saint Eustatius
(photo courtesy of Frogfish Photography)


Sand temperatures for nesting sea turtles in the Caribbean: implications for hatchling sex ratios in the face of climate change” was published by the Journal of Experimental Marine Biology and Ecology (2016). Authors: Jacques-Olivier Laloë, Nicole Esteban, Jessica Berkel and Graeme C Hays.

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The case of the black turtle

How many species of sea turtle are there? Depending on who you ask, you might get a different answer. Some might say eight, others will say seven. The debated eighth species of sea turtle is the black turtle.

To trace back the history of the black turtle, one important event stands out: sometime between 3 and 20 million years ago Central America rose up out of the sea. The creation of the Isthmus of Panama was an important paleozoogeographic event that allowed for the migration of terrestrial species between the two American continents. On the other hand, this created a land barrier between the Atlantic and the Pacific, isolating two populations of green turtles from each other. One population that is found in the area from southern California to Chile and around the Galapagos islands looks different from all other green turtles: individuals are smaller in size, their carapace is oval shaped and tapered towards the tail, and they are darker in colour. Because of this last trait, they were given the common name ‘black turtle’, but it is also known by some as the Eastern Pacific green or the Galapagos green turtle.

A juvenile black sea turtle (right) next to a juvenile green sea turtle (photo taken by Javier Rodríguez-Zuluaga, courtesy of PLoS One)

A juvenile black sea turtle (right) next to a juvenile green sea turtle (left)
(photo taken by Javier Rodríguez-Zuluaga, courtesy of PLoS One)

But is the black turtle a unique species? Studies of skull anatomy suggest that black turtles are indeed different to green turtle. On the other hand, DNA analyses reveal no genetic distinction between the two turtle populations. There is still ongoing scientific debate as to whether or not the black turtle should be considered a stand-alone species, or possibly a subspecies. Officially, neither the species Chelonia agassizii nor the subspecies Chelonia mydas agassizii are recognized but both continue to be widely used by scientists.

I contacted Dr Jeffrey Seminoff from NOAA who wrote his dissertation on black turtles in 2002. “Taxonomy is not a static thing and there will always be disagreement among scientific colleagues on the topic,” he tells me. “Today it is not an argument that I prefer to spend energy on. Instead, I am focusing on the fantastic population recovery of black (i.e. green) turtles in the eastern Pacific. These dark green turtles are doing very well currently, but we need to keep our focus on efforts to preserve this recovery!”

Regardless of their taxonomic status, it is great to hear that devoted scientists are successfully preserving these mysterious turtles!

Plastic pollution

Plastic pollution in the oceans is a real problem that is often easily set aside because we do not see its effects in our daily lives. Occasionally, however, we are reminded of the dramatic consequences that plastic pollution has on life in the oceans.

A group of marine biologists led by Christine Figgener working in Costa Rica came across a male olive ridley with what appeared to be a parasitic worm inside its nostril. After careful inspection, it turned out that the foreign object was in fact a plastic drinking straw. The researchers, who were a few hours from the nearest vet and x-ray machines, were able to successfully remove the straw with a pair of pliers on the boat.

I communicated about the event with herpetologist and sea turtle expert Prof. Jeanette Wyneken from Florida Atlantic University. She tells me that “anatomically, cheloniid (or hard-shelled) sea turtles have a partial secondary palate between the nostrils and the mouth. […] The straw looks like it was in that space, possibly extending along the lateral part of the nasal sac but it could have gone through the choana into the mouth.” Furthermore Prof. Wyneken explains that “turtles, like many reptiles, wall-off foreign bodies with caseous material and fibrin (sort of a scaffolding of protein). That is likely why the straw was so hard to remove. The bleeding nose was likely due to those fibrin components being torn away from the normal lining.”

Thankfully the turtle is reported to have been in good health and was promptly released. “The bleeding stopped pretty much immediately after the removal of the straw,” reported Ms Figgener. “We disinfected the air passageway with iodine and kept the turtle for observation before releasing him back into the wild.[…] He did very obviously not enjoy the procedure very much, but we hope that he is now able to breathe more freely.”

Let’s hope that this video serves as a reminder to be responsible with the disposal of our waste, especially plastic waste. You just never know where your garbage might end up.

Video courtesy of The Leatherback Trust

Identifying sea turtle species

There are seven species of sea turtles and to the untrained eye they look somewhat similar. In fact, turtles are often misidentified in the press: it is not rare to see the picture of a green turtle next to an article about loggerhead turtles. So how can you correctly identify the species of a turtle?

Leatherback turtles are easy to recognize because of their unique soft leathery back. For the other six species it is a bit trickier. The key to correctly identifying a turtle species is by examining its shell and the pattern of its scales (also known as scutes).

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The name of the different scutes on a sea turtle carapace

By counting the costal scutes on a turtle’s carapace and the prefrontal scales on its head, you can tell each species apart. For example, hawksbill turtles have four costal scutes on each side of their carapace and two pairs of prefrontal scales on their head unlike green turtles that have four costal scutes but only one pair of prefrontal scales. By using the following turtle identification key you can easily identify the seven species of sea turtles. Alternatively, check out this interactive species identification key from the very informative Sea Turtle Conservancy.

Sea turtle identification key (courtesy of seaturtle.org)

Sea turtle identification key
(courtesy of seaturtle.org)

Of course there are other ways to quickly identifying turtle species. For example, loggerheads have a typically large head and a beautiful red-orange colour. With experience you learn how to tell apart one species from the other without resorting to counting scutes, but examining the carapace is always a sure way to confirm your identification!

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Can you identify the species of this juvenile sea turtle?

Happy World Sea Turtle Day!

World Sea Turtle Day is celebrated on June 16th every year. The date was chosen because it is the birthday of sea turtle conservation pioneer Archie Carr (1909-1987). Dr Carr understood early on the importance of sea turtles for the oceans. He also  realized that in certain parts of the world populations of sea turtles were at serious threat of disappearing and he devoted decades of his life to understanding and protecting sea turtles. He was the founding scientific director of the Sea Turtle Conservancy and did renowned research in Tortuguero, Costa Rica. Much of what we know today about the biology and life cycle of marine turtles stems from his lifetime of work on sea turtles.

Unfortunately sea turtles are still endangered today. Threats include marine pollution, coastal squeezesea level rise, and global warming. One of the purposes of World Sea Turtle Day is to raise awareness of the ongoing plight of sea turtles. It is a day to learn about, honour, and celebrate the wonderful creatures that are sea turtles. If you want to do something for sea turtles today, check out this link and spread the word. Happy World Sea Turtle Day to all!

Dr Archie Carr with a green sea turtle (photo taken by Jeanne Mortimer, courtesy of the Sea)

Dr Archie Carr with a green sea turtle
(photo taken by Jeanne Mortimer, courtesy of the Sea Turtle Conservancy)

Titanium turtle

Every year boat strikes contribute to the anthropogenic mortality of several threatened marine species including sea turtles, manatees, dugongs, and whales. A boat strike will often result in severe injury and the animal’s death.

However, for the male loggerhead turtle “Akut-3” the story is different. The turtle, named after the Search & Rescue Association that found him, was taken to the DEKAMER Sea Turtle Research, Rescue and Rehabilitation Centre after he was found badly injured and floating off the shores of Turkey. Akut-3 had visibly had a close encounter with a boat propeller: he suffered from severe facial wounds and a fractured jaw. With over 60% of his jaw missing and unable to feed anymore, this turtle’s fate seemed sealed.

The only hope was total facial reconstruction. Working in collaboration with BTech Innovation A.Ş. the veterinary surgeons designed an implant for the turtle and had it 3D printed using medical-grade titanium. After a successful operation, Akup-3 is still recovering at the DEKAMER Centre.

This is the first time a sea turtle benefits from 3D printing technology. As of yet, the turtle does not show any signs of rejecting the implant but it will take time before it is confirmed that the operation was a complete success. Let’s hope that the turtle can be fully rehabilitated and released back into the wild!

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Photos courtesy of BTech Innovation A.Ş..

The Annual Symposium on Sea Turtle Biology and Conservation

The 35th Annual Symposium on Sea Turtle Biology and Conservation, organized by the International Sea Turtle Society, will be held from 18-24 April in Dalaman-Muğla, Turkey. At this event researchers and conservationists get together to discuss the latest advances in the field.

This is the first year that I am able to attend the symposium and I will give an oral presentation titled “250-year reconstructions of incubation temperatures: predicting climate change impacts on the viability of marine turtle populations.” My presentation is part of the Fisheries and Threats session. In this talk I will present some of my work that was published last year in the journal Nature Climate Change. You can find more information about my talk in the book of abstracts of the symposium. You can also read about the other talks in the symposium’s program.

I am really looking forward to meeting the leading scientists in my field of research, to receive feedback and constructive criticism on my work, and to learn about the latest work of others in the field!

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I would also like to thank all the sponsors of the symposium and the Marine Biology Association of the UK for their generous support to help me attend the symposium.