World Sea Turtle Day 2017

One of our members, Rushan is currently undertaking his honours year in Murdoch University, using airborne LiDAR-derived topographic maps to determine the importance of beach topography on nest site selection by flatback sea turtles. He has also been involved in hatchery management, captive-rear and release, and sea turtle nursing in the Maldives, Malaysia, and Singapore. This post was contributed by him to commemorate World Sea Turtle Day

June 16th has been declared as World Sea Turtle Day in honor of Dr. Archie Carr. His work brought the plight of sea turtles to the forefront of our attention, and it was through his work that turned the sea turtles around on their path to extinction towards their recovery.

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Dr. Archie Carr placing a satellite tag on a green sea turtle. PHOTO CREDIT: Archie Carr Center for Sea Turtle Research, University of Florida

The fossil record indicates that the oceans were once populated with thousands of species of sea turtles, but this legacy is currently held by seven extant species of sea turtles today. Though there are seven sea turtles species today, each species is naturally  divided into several different populations, either by barriers to migration or movement of currents during their pelagic phase. These populations can be roughly divided into Regional Management Units, which are discrete populations of sea turtles that appear to use different oceans and nesting grounds from other populations of the same species. So different are these different populations, in fact, that their conditions for nest site selection can also greatly vary.

Last year for World Sea Turtle Day, I gave a brief overview of the life cycle of sea turtles, as well as talked about the two most commonly found sea turtles in Singapore. This year, I will talk about each sea turtle species in an easy-to-refer info-style format. Specifically, I will cover the conservation status, distribution, the regional management units, diet, threats, and the most prominent feature for each species.

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Size comparison chart of the extant species of sea turtles and the extinct Archelon. PHOTO CREDIT: National Aquarium

 

 

HAWKSBILL SEA TURTLE

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The scales on the sides of the head of Hawksbill Sea Turtles are often snapped an analyzed as these can be used to tell individuals apart. PHOTO CREDIT: Rushan bin Abdul Rahman

Scientific Name: Eretmochelys imbricata
Conservation Status: Critically Endangered
In-water Distribution: Primarily tropical, with lesser extent in subtropical waters of the Atlantic, Indian, and Pacific Ocean.
Nesting Distribution: Tropical (Caribbean, Central America, South America, Africa, Madagascar, India, Maldives, Indonesia, Malaysia, Singapore, Australia)
Regional Management Units: East, West, and Southwest Atlantic; Eastern and Southwest Pacific.
Diet: Primarily feed on sponges, but can also be seen eating small crustaceans.
Threats: The most prominent threat to hawksbill sea turtles is the tortoiseshell trade. The beautiful patterns seen on their carapace are highly prized by consumers for accessories such as combs and bracelets.
Most Prominent Feature: Its beak, hence the name Hawksbill Sea Turtle. The head is long and narrow with a large beak, which allows the sea turtle to reach into tiny crevices within the coral and rip out sponges.

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Hawksbill Sea Turtles are often poached for their shells, which are then used to make accessories such as combs, bracelets, and hairbands.

 

GREEN SEA TURTLE

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A Green Sea Turtle in the blue waters of the Maldives. PHOTO CREDIT: Chiara Fumagalli

Scientific Name: Chelonia mydas
Conservation Status: Endangered
In-water Distribution: Tropical, with sightings seen as far north as the United Kingdom, but most likely passively drifted there when it was caught in the wrong current stream.
Nesting Distribution: Tropical, as far north as southern Japan and as far south as Southern Madagascar.
Regional Management Units: East, Northwest, South, Central, Southwest, and South Caribbean Atlantic; Northeast, Northwest, Southeast, and Southwest Indian Ocean; Mediterranean; East, North Central, Northwest, South Central, Southwest, West Central, and Western Pacific (i.e. South East Asia, of which Singapore is a part of).
Diet: Green Sea Turtles are omnivorous when they are neonates and juveniles, but switch to an herbivorous diet of sea grass when they recruit into near-shore environments. Adults have been seen eating jelly fish.
Threats: The most prominent threat to Green Sea Turtles is the harvesting of eggs and adults on nesting beaches for food. Some countries allow for the legal take of eggs and adults despite their international conservation status. However, countries that do have legislation protecting nesting beaches of Green Sea Turtles have rampant black markets for Green Sea Turtle products.
Most Prominent Feature: Adult green sea turtles really are very green, which is attributed to their herbivorous diet. They have gentle looking faces, which suits their personality as one of the more gentle sea turtle species in the world.

 

LOGGERHEAD SEA TURTLE

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A juvenile Loggerhead Sea Turtle in Uruguay. PHOTO CREDIT: Alejandro Fallabrino

Scientific Name: Caretta caretta
Conservation Status: Vulnerable
In-water Distribution: Tropical, Sub-tropical, and has been found in some temperate waters
Nesting Distribution: Tropical and temperate waters such as the Gulf of Mexico, Central America, South Africa, Shark Bay in Australia, southern Japan.
Regional Management Units: Northeast, Northwest, and Southwest Atlantic Ocean; the Mediterranean; Northeast, Northwest, Southeast, and Southwest Indian Ocean; and the North and South Pacific.
Diet: Mainly crustaceans.
Threats: Prominent threats are fisheries bycatch and direct take of eggs and adults on nesting beaches.
Most Prominent Feature: Their heads are huge, hence the name Loggerhead Sea Turtle. Their heads are muscular and designed to crush and crack the hard exoskeletons of crustaceans.

 

FLATBACK SEA TURTLE

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A Flatback Sea Turtle on a Port Hedland beach in Western Australia. This particular individual had a very high clearance! PHOTO CREDIT: Linda Reinhold

Scientific Name: Natator depressus
Conservation Status: Needs Updating
In-water Distribution: Only found in the waters of temperate and tropical Australia, from Queensland through the Torres Straits in Northern Territory and Papua New Guinea, the Kimberley’s, Pilbara, Ningaloo Reef and Shark’s Bay.
Nesting Distribution: Queensland, Northern Territory, the Kimberley’s, Pilbara, Eighty Mile Beach, Shark’s Bay.
Regional Management Units: Southeast Indian Ocean and Southwest Pacific Ocean, but more management units may be delineated with additional genetic information.
Diet: Soft-bodied invertebrates
Threats: Currently unclear, though there have been records of direct predation by invasive foxes and feral dogs, habitat degradation, and bycatch.
Most Prominent Feature: True to their name, flatback turtles are indeed very flat turtles.

 

OLIVE RIDLEY SEA TURTLE

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An Olive Ridley Sea Turtle lumbering on the beach. PHOTO CREDIT: Laura Carruyo-Rincón

Scientific Name: Lepidochelys olivacea
Conservation Status: Vulnerable
In-water Distribution: Tropical
Nesting Distribution: Tropical: Central America, South America, Africa, Sri Lanka and India, Malaysia, and several nesting populations in tropical Australia.
Regional Management Units: East and West Atlantic Ocean; Northeast Indian Ocean; the Northeast Indian arribada Ocean population, and the West Indian Ocean; Eastern Pacific, Eastern arribada Pacific population, and the Western Pacific Ocean population.
Diet: Oceanic jelly fish
Threats: The greatest threat to Olive Ridley Sea Turtles are direct exploitation at nesting beaches. Arribada populations, such as in northern India, see mass nesting of females on single nights, where their eggs or adults are easily picked off.
Most Prominent Feature: The smallest sea turtle in the world, with a round to heart-shaped carapace. They also under arribadas, which is the mass nesting of females. Males appear to stay pelagic throughout their life, only mating with females when en route to breeding waters.

 

KEMP’S RIDLEY SEA TURTLE

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A nesting Kemp’s Ridley Sea Turtle in Rancho Nuevo, Tamaulipas, Mexico in 2017. PHOTO CREDIT: Alejandro Fallabrino

Scientific Name: Lepidochelys kempii
Conservation Status: Critically Endangered
In-water Distribution: The Gulf of Mexico and Northern Atlantic (East Coast of the United States to the West Coast of Europe)
Nesting Distribution: Currently only nesting in the Gulf of Mexico
Regional Management Unit: Only one Regional Management Unit identified, which is the Northwest Atlantic Ocean RMU, which includes the Gulf of Mexico and the entire eastern seaboard of the United States.
Diet: Crustaceans, soft-bodied invertebrates
Threats: Direct take of eggs and adults during their arribada in a single site in the United States has caused the population to plummet. Conservation actions for the Kemp’s Ridley Sea Turtle were relocating nests in the Gulf of Mexico and incubating them on beaches on Padre Island, Texas, as well as releasing juveniles from captive-rear and release programs.
Most Prominent Feature: If you happen to be in the Gulf of Mexico and stumble upon a mass nesting event of sea turtles, it is more than likely that you have come across Kemp’s Ridley Sea Turtles. These sea turtles, like the Olive Ridley Sea Turtles, undertake the arribada, though their nesting populations have plummeted. In addition, their heads are narrower and longer than Olive Ridley Sea Turtles.

 

LEATHERBACK SEA TURTLES

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From little things to big things: a female Leatherback Sea Turtle nesting adjacent to a hatchling running for the water. PHOTO CREDIT: Linda Reinhold

Scientific Name: Dermochelys coriacea
Conservation Status: Vulnerable
In-water Distribution: Have the widest distribution of all sea turtles, having been seen as far north as Norway and as far south as Patagonia. This is attributed to their size, as they have grown so large that they are able to generate their own heat, and hence are able to tolerate more frigid waters.
Nesting Distribution: Tropical and sub-tropical, with populations in east and west coast of the United States, Caribbean, southern and western Africa, Indonesia, Malaysia, Sri Lanka, and northern Australia.
Regional Management Units: Northeast, Southeast, and Southwest Atlantic Oceans; Northeast and Southwest Indian Oceans; East and West Pacific Ocean.
Diet: Pelagic jellyfish.
Threats: Bycatch and direct take of adults and eggs are direct threats to the populations, while coastal development of their nesting grounds prevents them from nesting and bringing in new recruits into the populations.
Most Prominent Feature: Their size. These are the largest sea turtles in the world and are a phenomenal animal to be in the presence of. Their common and scientific name is also attributed to the fact that leatherbacks do not have a hard carapace, but rather a leathery skin layer.

 

HAWKSBILL AND GREEN SEA TURTLES OF SINGAPORE

Hawksbill and green sea turtles have been recorded in Singapore on several occasions, with the former finding nesting areas on the beaches within Singapore. The leatherback sea turtle has only been recorded once in Singapore, with the specimen taken and preserved in the now Lee Kong Chian Natural History Museum.

There are several conservation actions being taken in Singapore. For example, Sisters’ Islands has recently been declared as a Marine Park, with plans to establish a sea turtle hatchery on the island. Considering that Singapore coastlines and beaches are constantly used by visitors, translocating sea turtle nests to a hatchery far away from the hustle and bustle of urban Singapore may be a much needed relief and safe haven for incubating nests.

It is coming to the peak nesting period for the local RMU, so if you happen to be on a beach at night, you may come across a nesting sea turtle. As excited as you may be, this is a very delicate process, which can easily be disrupted with the flashing of cameras and squealing of people. If you happen to come across a nesting sea turtle on any of our beaches, please follow these simple guidelines:

  1. Call the National Parks Board on their hotline at 1800 471 7300. Take note of your location (barbecue pit number, the zone you are in, etc.) so they are able to come down to the site.
  2. Do not approach a sea turtle emerging onto the beach to nest; sea turtles are incredibly sensitive to movement and lights, and may abort the entire procedure if they feel the slightest inclination that they are being threatened.
  3. Do not touch sea turtle hatchlings that are emerging from the ground as this is a very sensitive part of their life cycle. Give them plenty of space to go into the water, and maybe even remove trash that would be in their way.

Thanks for reading, and have a turtley awesome day!

World Sea Turtle Day

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Dr. Archie Carr (center) is regarded as the father of sea turtle biology, setting the foundations for the work of present and future sea turtle biologists around the world. (PHOTO CREDIT Dr. Archie Carr: Sea Turtle Conservancy; various sea turtles: Rushan bin Abdul Rahman)

June 16th is World Sea Turtle Day, made in honour of Dr. Archie Carr (June 16th, 1909 – May 21st, 1987), who has been regarded as the father of sea turtle biology. He founded the Sea Turtle Conservancy and turned the tide of sea turtle extinction into a road to recovery with many of his projects, from Operation Green Turtle to chairing the Marine Turtle Specialist Group of the IUCN for 20 years. His descriptive biology and ecological papers on the seven (or eight, depending on who you talk to) species of sea turtles have been the foundations for all sea turtle biologists worldwide to this day and for many years to come.

In celebration of World Sea Turtle Day, we will cover a bit on sea turtle biology and the fascinating life cycle of sea turtles, followed by the sea turtles found in Singapore and the perils they face. It is not all doom and gloom, as we will then talk about what you can do as the general public to make life a lot easier for our ancient and charismatic reptilian friends.

SEA TURTLE BIOLOGY

There are seven recognized species of sea turtles throughout the world: the Green Sea Turtle (Chelonia mydas), the Hawksbill Sea Turtle (Eretmochelys imbricata), the Loggerhead Sea Turtle (Caretta caretta), the Olive Ridley Sea Turtle (Lepidochelys olivacea), the Kemp’s Ridley Sea Turtle (Lepidochelys kempii), the Flatback Sea Turtle (Natator depressus), and the Leatherback Sea Turtle (Dermochelys coriacea). The first six fall into the family of Cheloniidae turtles (essentially sea turtles with scutes on their shells) while the Leatherback Sea Turtle is the only living representative of the Dermochelyiidae family (sea turtles with no scutes)1. Though these are the only living representatives of sea turtles, six are listed as vulnerable, endangered, or critically endangered under the International Union of Conservation of Nature Red List of Threatened Species2–6, while the Flatback Sea Turtle is listed as data deficient7.They are entirely marine, meaning they can only be found in the salt waters of the ocean, and despite being primarily sea-faring animals, they evolved from land turtles in the mid-Cretaceous8 and need to surface to breathe.

 

Green Sea Turtles (left) and Hawksbill Sea Turtles (right) are the two species of sea turtles that can be found in the waters surrounding Singapore. (PHOTO CREDITS Green Sea Turtle: Chiara Fumagalli [Maldives]; Hawksbill Sea Turtle: Rushan bin Abdul Rahman [Maldives])

THE CIRCLE OF LIFE

The life of sea turtles begins with a clutch of about 100 eggs in the sand at the beach. The sea turtles will hatch from the eggs between 45 to 60 days of incubation, but will not emerge from their nest just yet. When they hatch, they are born curved and with the yolk still attached to the bottom-shell (plastron), and take four to five days to straighten out and to absorb the yolk into their system. After this, they head towards the surface in a mad flurry, but will stay just below the surface of the sand and wait for nightfall when temperatures are cool. At that point, they come out of the sand and make a mad dash down the beach, into the water, and a mad “swim frenzy” out into open-ocean to catch ocean currents (Flatback Sea Turtle hatchlings, which are endemic to Australia, will not swim out to open-ocean but will stay within the nearshore habitats). From this point on, sea turtles will spend the rest of their lives in the ocean (with the exception of females, which will emerge onto the beach to lay their eggs).

Many sea turtle biologists agree that this is a very important part of the sea turtle life cycle, as this is where imprinting occurs (the act of sea turtle hatchlings remembering where they hatched from so they can return to the same nesting site to lay eggs when they are older)9,10. This is also the most dangerous part of their lives; predators abound on land and in sea, and many sea turtle hatchlings fall prey to ghost crabs, feral animals, birds, sharks, fish11,12.

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Hatchlings face a perilous journey from the moment they leave the nest; predators abound in every leg of their mad frenzy to reach offshore currents in open-ocean, with many of them not making it. Here, a Green Sea Turtle hatchling is observed making its way down the beach to the water. (PHOTO CREDITS Claire Gilby [Tioman Island])

Once in open-ocean, hatchlings are at the mercy of ocean currents. Some hatchlings hide out in rafts of Sargassum seaweed for several years, where they feed on anything they can find, such as small crustaceans and fish. Once they reach about a meter in length, some sea turtle species will recruit back to the near-shore reefs, such as Green Sea Turtles, Hawksbill Sea Turtles, and Loggerhead Sea Turtles. Leatherback Sea Turtles, Kemp’s and Olive Ridley Sea Turtles are turtles that live in open-ocean, though Leatherback Sea Turtles are known to dive to substantial depths to feed on jellyfish.

Within these habitats, sea turtles will forage for a good part of their lives, but every two or three years sea turtles will migrate to the sites from which they hatched in an event called natal-homing, which can be accurate to within a few kilometers1. Here, they will mate in the near-shore habitats, and the females will emerge onto the beach to lay their eggs (oviposition). Much of the oviposition occurs at night to avoid predation on themselves and on their eggs, but many other factors will determine where a sea turtle may nest13–15. The female will first dig a body pit with the front flippers, followed by them turning 180º and digging an egg chamber with their hind flippers. They will then lay an average of 100 eggs in each egg chamber (depending on the species), where the whole process will begin again.

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A clutch of eggs that was translocated to a hatchery at the Juara Turtle Project on Tioman Island. Each clutch averages at about 100 eggs, but this value varies depending on the species of sea turtle. Clutches are often translocated when the clutch in their original site run the risk of 100% mortality. (PHOTO CREDIT Sadhana Jayaseelan [Tioman Island])

The Ridley Sea Turtles undertake a phenomenal mass-nesting event called the arribada, where thousands of individuals will emerge onto the beaches to nest at once. Several hypotheses have been raised as to why they aggregate to mate and nest en masse, from predator saturation to being able to find mates easier in the water16.

SEA TURTLES OF SINGAPORE

Two species of sea turtles frequent the waters of our little red dot: the Green Sea Turtles and the Hawksbill Sea Turtles17. A single Leatherback Sea Turtle specimen was recovered in 1883, but no other Leatherback Sea Turtle sighting in Singapore territorial waters has been reported since18.

So far, there has been no evidence of Green Sea Turtles nesting on Singapore beaches, but there have been several reports of Hawksbill Sea Turtles nesting and hatching from our beaches19,20. This may be attributed to the nest site selections of the two species, where Green Sea Turtles prefer level and open-expanses of beaches with deep nesting chambers13,21, while Hawksbill Sea Turtles are happy to nest in dense vegetation along beaches22. That said, because many of the beaches in Singapore are reclaimed and artificial23, the nesting habitats are barely suitable for sea turtles in general, let alone for Green Sea Turtles.

THREATS WITHIN SINGAPORE

Nesting Hawksbill Sea Turtles in Singapore are worth celebrating, especially for a heavily urbanized island-state like ours, but they still face a multitude of threats. A single news report on poached sea turtle eggs in Singapore highlights the dangers of this activity24, and possibly that many other poaching incidents go unreported. Females will not go onto well-lit beaches, while hatchlings can be mis- or disorientated and head towards artificial light sources rather than the ocean25. Climate change can spell disaster for sea turtles as well, as rising sea levels can drown and kill entire clutches of sea turtle eggs26. Further, because sea turtle gender is temperature-dependent, where warmer temperatures produce more females and cooler temperatures produce more males, global warming can cause clutches to be entirely female, leaving no males to mate with them and resulting massive population crashes27. That is assuming temperatures do not go above the lethal threshold, after which entire clutches of sea turtle eggs can die28. The heavy boat traffic in Singapore can also increase the potential of sea turtles dying from boat strikes.

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Dead embryo and completely undeveloped yolk excavated from a nest in the Juara Turtle Project hatchery on Tioman Island. High temperatures can “cook” sea turtle eggs, killing the embryo within them. Embryo deaths can occur at any stage of development (PHOTO CREDIT Rushan bin Abdul Rahman [Tioman Island])

There are future plans for managing the incidents of sea turtles within Singapore, which will possibly mitigate the impact on the species. The National Parks Board has announced that a sea turtle hatchery will be opened on Sisters’ Island Marine Park as a means of moving sea turtle clutches found on mainland Singapore that are in danger of mortality. This hatchery is scheduled to be operational by end-2017.

WHAT CAN WE DO?

The picture painted for sea turtles in Singapore is not a pretty one, but there are things that everyday Singaporeans can do to reduce the threats to sea turtles in Singapore:

  1. Ensure that trash you bring to the beaches is disposed of properly within the designated bins in our coastal parks. Better yet, adopt a pack-in-pack-out mentality of taking whatever trash is brought into our coastal parks back out of the coastal parks and disposed responsibly elsewhere.
  2. Do not approach a sea turtle emerging onto the beach to nest; sea turtles are incredibly sensitive to movement and lights, and may abort the entire procedure if they feel the slightest inclination that they are being threatened.
  3. Do not touch sea turtle hatchlings that are emerging from the ground as this is a very sensitive part of their life cycle. Give them plenty of space to go into the water, and maybe even remove trash that would be in their way.
  4. If you do see a sea turtle on the beach, whether it is a nesting female or a hatchling, call the National Parks Board on their hotline at 1800 471 7300. Take note of your location (barbecue pit number, the zone you are in, etc.) so they are able to come down to the site.
Rushan is an environmental science honours student in Murdoch University undertaking a project using airborne laser scanning to see what aspects of beach topography sea turtles prefer for a nesting site. He has volunteered and interned with the Juara Turtle Project (Tioman Island, Malaysia), Seamarc Pvt. Ltd. (Maldives), and the National Parks Board (Singapore) working on various projects with hatchery management, a captive-rear-and-release program, sea turtle nursing and husbandry, identification of individual sea turtles, satellite tagging (ARGOS SPOT5) and satellite tracking. Upon completion of his course in July 2017, he hopes to continue working with sea turtles in Singapore and abroad.

REFERENCES CITED

  1. Bowen, B. W. & Karl, S. A. Population genetics and phylogeography of sea turtles. Mol. Ecol. 16, 4886–4907 (2007).
  2. Mortimer, J. A. & Donnelly, M. Eretmochelys imbricata. The IUCN Red List of Threatened Species e.T8005A12881238 (2008). doi:http://dx.doi.org/10.2305/IUCN.UK.2008.RLTS.T8005A12881238.en
  3. Casale, P. & Tucker, A. D. Caretta caretta. The IUCN Red List of Threatened Species e.T3897A83157651 (2015). doi:http://dx.doi.org/10.2305/IUCN.UK.2015-4.RLTS.T3897A83157651.en
  4. Abreu-Grobois, A. & Plotkin, P. Lepidochelys olivacea. The IUCN Red List of Threatened Species e.T11534A3292503 (2008). doi:http://dx.doi.org/10.2305/IUCN.UK.2008.RLTS.T11534A3292503.en
  5. Marine Turtle Specialist Group. Lepidochelys kempii. The IUCN Red List of Threatened Species e.T11533A3292342 (1996). doi:http://dx.doi.org/10.2305/IUCN.UK.1996.RLTS.T11533A3292342.en
  6. Wallace, B. P., Tiwari, M. & Girondot, M. Dermochelys coriacea. The IUCN Red List of Threatened Species (2013). doi:http://dx.doi.org/10.2305/IUCN.UK.2013-2.RLTS.T6494A43526147.en
  7. Red List Standards & Petitions Subcommittee. Natator depressus. The IUCN Red List of Threatened Species e.T14363A4435952 (1996). doi:http://dx.doi.org/10.2305/IUCN.UK.1996.RLTS.T14363A4435952.en
  8. Wang, Z. et al. The draft genomes of soft-shell turtle and green sea turtle yield insights into the development and evolution of the turtle-specific body plan. Nat. Genet. 45, 701–706 (2013).
  9. Brothers, J. R. & Lohmann, K. J. Evidence for geomagnetic imprinting and magnetic navigation in the natal homing of sea turtles. Curr. Biol. 25, 392–396 (2015).
  10. Lohmann, K. J., Lohmann, C. M. F., Brothers, J. R. & Putman, N. F. in Biology of Sea Turtles: Volume III (eds. Wyneken, J., Lohmann, K. J. & Musick, J. A.) 59–78 (CRC Press Taylor & Francis Group, 2013).
  11. Peterson, C. H., Fegley, S. R., Voss, C. M., Marschhauser, S. R. & VanDusen, B. M. Conservation implications of density-dependent predation by ghost crabs on hatchling sea turtles running the gauntlet to the sea. Mar. Biol. 160, 629–640 (2013).
  12. Burger, J. & Gochfeld, M. Avian predation on olive ridley (Lepidochelys olivacea) sea turtle eggs and hatchlings: Avian opportunities, turtle avoidance, and human protection. Copeia 1, 109–122 (2014).
  13. Zavaleta-Lizarraga, L. & Morales-Mavil, J. E. Nest site selection by the green turtle (Chelonia mydas) in a beach of the north of Veracruz, Mexico. Rev. Mex. Biodivers. 84, 927–937 (2013).
  14. Serafini, T. Z., Lopez, G. G. & Da Rocha, P. L. B. Nest site selection and hatching success of hawksbill and loggerhead sea turtles (Testudines, Cheloniidae) at Arembepe Beach, northeastern Brazil. Phyllomedusa 8, 3–17 (2009).
  15. Spanier, M. J. Beach erosion and nest site selection by the leatherback sea turtle Dermochelys coriacea (Testudines: Dermochelyidae) and implications for management practices at Playa Gandoca, Costa Rica. Rev. Biol. Trop. 58, 1237–46 (2010).
  16. Bernardo, J. & Plotkin, P. T. in Biology and Conservation of Ridley Sea Turtles (ed. Plotkin, P. T.) 59 – 87 (John Hopkins University Press, 2007).
  17. Tan, R. Sea turtles. Wild Singapore (2010).
  18. Diong, C. H. in Assessment of the conservation status of the leatherback turtle in the Indian Ocean and South-East Asia. IOSEA Species Assessment: Volume I 120–121 (Secretariat of the Indian Ocean – South-East Asian Marine Turtle Memorandum of Understanding, 2006).
  19. Chua, G. Rare sea turtle spotted on beach at East Coast Park. The Straits Times (2013).
  20. Basu, R. Rollerbladers rescue baby turtles at East Coast. The Straits Times (2007). at <http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes20060526-1.2.60.22.aspx&gt;
  21. Chen, T. H. & Cheng, I. Breeding biology of the green turtle, Chelonia mydas, (Reptilia: Cheloniidae) on Wan-An Island, Peng-Hu Archipelago, Taiwan. I. Nesting Ecology. Mar. Biol. 124, 9–15 (1995).
  22. Zare, R., Vaghefi, M. & Kamel, S. Nest location and clutch success of the hawksbill sea turtle (Eretmochelys imbricata) at Shidvar Island, Iran. Chelonian Conserv. Biol. 11, 229–234 (2012).
  23. Lai, S., Loke, L. H. L., Hilton, M. J., Bouma, T. J. & Todd, P. A. The effects of urbanisation on coastal habitats and the potential for ecological engineering: A Singapore case study. Ocean Coast. Manag. 103, 78–85 (2015).
  24. Jian, H. 无良公众挖走逾百海龟蛋. 新明日报 (2013).
  25. Salmon, M. Artificial night lighting and sea turtles. Biol. 50, 163–168 (2003).
  26. Shaw, K. R. Effects of inundation on hatch success of loggerhead sea turtle (Caretta caretta) nests. (2013).
  27. Tomillo, P. S. et al. High beach temperatures increased female-biased primary sex ratios but reduced output of female hatchlings in the leatherback turtle. Biol. Conserv. 176, 71–79 (2014)
  28. Wood, A., Booth, D. T. & Limpus, C. J. Sun exposure, nest temperature and loggerhead turtle hatchlings: Implications for beach shading management strategies at sea turtle rookeries. J. Exp. Mar. Bio. Ecol. 451, 105–114 (2014).