World Turtle Day丨Did you know? Sea turtles, which have existed for more than 200 million years, are on the verge of extinction...

Sea turtles, an ancient and magical large marine reptile, have existed on Earth for more than 200 million years. They move from the dangerous land to the wandering ocean, and can be found in all oceans except the polar waters.

Who are the members of the turtle family?

Currently, most scientists believe that there are seven species of sea turtles in the world. The largest of these is the leatherback turtle, Dermochelys coriacea, which can have a carapace length of up to 2 meters and weigh more than 900 kilograms. Its back is dark blue or black with white spots and seven conspicuous light-colored longitudinal ridges. Unlike other sea turtles, the leatherback turtle has a leathery skin and no keratinous shields [1], so people also call it a sea turtle. It is widely distributed in the Pacific, Atlantic, and Indian Oceans.

Leatherback turtles laying eggs on the beach (Photo from http://www.arkive.org/)

The carapace scales of the Hawksbill Turtle Eretmochelys imbricate have regular radial patterns, with yellow, brown and black colors mixed together. People have realized the aesthetic value of this pattern since a very early time. The most distinctive feature of the Hawksbill Turtle is that its upper beak is like an eagle's beak, and there are 13 carapaces on its back, one covering another like tiles. The carapaces on the sides are called marginal shields, and the closer they are to the buttocks, the more serrated they are. In addition, the plastron of the Hawksbill Turtle has two obvious longitudinal ridges. Currently, taxonomists believe that there are two subspecies of Hawksbill Turtle, namely the nominative subspecies (Atlantic subspecies) Eretmochelys imbricataimbricata and the Pacific subspecies Eretmochelys imbricatabissa.

Hawksbill turtle (Photo from http://www.arkive.org/)

The green turtle, Chelonia mydas, has a carapace pattern that is somewhat similar to the hawksbill turtle. It is named for its green fat. Most green turtles have irregular dark patterns on their carapaces. Some of them are like hawksbills, and the number of middle carapaces is also 13, the same as hawksbills. However, the carapace of the green turtle is flat, the marginal shield is not serrated, and the forehead scales on the head are a pair of long, the upper beak is not like an eagle's beak, and the plastron does not have strong longitudinal ridges. Green turtles are widely distributed in the Pacific, Atlantic and Indian Oceans.

Green sea turtle (Photo from http://alpha-divers.pl/)

The flatback turtle, also known as the flatback sea turtle Natatorde pressus, has only one pair of forehead scales, a gray-green carapace, 13 flat scales in the middle of the carapace, and no serrations on the marginal shields. They have a single color with almost no pattern. The edges of the marginal shields are brownish yellow, while the edges of the carapace are a beautiful dark color. What's more interesting is that their dorsal spine is not convex, but flat (hence the name flatback turtle). Flatback turtles only live in the oceans around Australia.

Flatback turtle (Photo from http://www.seaturtles911.org/)

The loggerhead turtle, also known as the loggerhead turtle Caretta caretta, has flat carapace scales and non-serrated marginal shields. However, it has two pairs of frontal scales on its head and 15 carapace scales. The color is reddish brown with no pattern, which corresponds to its name. The plastron (chest) is flat. Like the green turtle, it is also widely distributed in the Pacific, Atlantic and Indian Oceans.

Loggerhead turtle (Photo from http://www.arkive.org/)

Similar to the loggerhead turtle is the Olive Ridley family. This small family are all olive green and have two forehead scales. Unlike other sea turtles, they are small, oblate, and have a lot of scales in the middle of their carapace. The ancestors of this small family were separated into two species by the uplift of Central and South America three or four million years ago, namely the Atlantic Olive Ridley Lepidochelys kempii (also known as Kemp's Ridley) and the Pacific Olive Ridley Lepidochelys olivacea. Among them, the Pacific Olive Ridley has a very small head, the most scales in the middle of its carapace, which can reach more than 17, and its plastron is light orange-yellow. This species is mainly distributed in the tropical regions of the Pacific and Indian Oceans. The Atlantic Olive Ridley is the smallest, with 15 scales on its carapace and a white or slightly yellowish plastron. It mainly lives in the tropical waters west of the Atlantic Ocean.

Olive ridley (Photo from http://www.arkive.org/)

Pacific turtle (Photo from http://www.californiaherps.com/)

Are turtles also afraid of drowning?

Compared to other terrestrial or freshwater turtles, sea turtles have a more spindle-shaped body. This streamlined body is more suitable for swimming, but it also reduces the volume of the shell, so their heads and limbs cannot be retracted into the shell like most turtles. Like other reptiles, sea turtles breathe with lungs, so they need to come to the surface of the water from time to time to breathe. They cannot breathe by contracting and relaxing their ribs, but can only rely on the muscles around their lungs to complete this process.

The diving ability of turtles depends on their activity level. Foraging turtles can stay underwater for 5-40 minutes, while sleeping turtles can stay underwater for 4-7 hours. If entangled in fishing nets, turtles will be more likely to drown due to stress.

Why do sea turtles grow so big?

In the first 3-5 years of their lives, sea turtles spend most of their time in the seaweed colonies in the pelagic zone, and green turtles particularly like to stay in the Sargassum colonies. These giant seaweed colonies, like dense forests, provide food and shelter for sea turtles. The vastness of their living environment plays an important role in the reason why sea turtles can grow so large. Another equally important reason is long-distance migration. After mating in the sea, females often migrate thousands of miles to reach the egg-laying site. Some females even return to the beach where they hatched to lay eggs. This phenomenon, called the homing impulse, is expressed to varying degrees in various sea turtles. The mechanism of how they find their way home is not yet fully understood. Some existing theories believe that the magnetic substances in the turtles' brains play a role similar to a compass.

The global distribution of sea turtle nesting sites (Image source: UNEPWCMC)

Inheriting life, from water to land

Sea turtles lay eggs every 2-4 years after they reach sexual maturity. Egg laying usually takes place at night, and the mother turtle will drag her huge body to the shore with difficulty. Her paddle-like limbs, which are very comfortable in the sea, seem a bit clumsy at this time. They use their flippers to dig holes in the beach, and some sea turtles can lay more than 300 eggs at a time. After laying eggs, they will carefully cover the eggs with soil, smooth out the traces of digging holes, and camouflage their nests with plants, and then return to the sea exhausted.

A green sea turtle digging a hole to lay its eggs (Photo credit: Kevin Schafer)

The Arena of Life

The life of a sea turtle is full of dangers and challenges. When they are still eggs, maggots, fungi, crabs, wild dogs, raccoons, birds, etc. are always threatening their survival. For the newly born baby turtles, the world is even more dangerous, and now they must rush to the ocean as quickly as possible. Predators have been waiting near the beach before they are born, ready to have a full meal, and even in the sea, there are sharks and fishing nets waiting for them. The beach where humans usually sing and dance has become a cruel arena for the little turtles. However, some turtles have come up with a way to deal with it. Unlike most other turtles that lay eggs at night, the Atlantic ridley chooses to lay eggs collectively during the day. The huge number of eggs and hatching increases the survival rate of individuals. This is the famous Arribada phenomenon.

The small town of Ostional in Costa Rica welcomes the spectacular Arribada phenomenon every year. Since the 1980s, people here have been allowed to obtain turtle eggs for use or sale during the Arribada phenomenon under certain conditions. (Photo credit: Dave Sherwood)

Hard-working ocean gardener

Sea turtles are hardworking gardeners in the ocean. As one of the few large marine organisms that feed on seagrass, they constantly "prune" the seagrass to promote its better growth. The health of the seagrass beds is closely related to them, and many marine organisms that survive on seagrass beds benefit from it. In addition, the eggs laid by sea turtles on the beach, whether hatched or not, provide a large amount of nutrients for the beach, promote the growth of dune vegetation, and reduce beach weathering.

Where have the domestic sea turtles gone?

Sea turtles seem to have nothing to do with China, so how can there be domestic sea turtles? In fact, there are five species of sea turtles distributed in my country, namely green turtles, loggerhead turtles, hawksbill turtles, olive ridley turtles and leatherback turtles. Most of them are distributed in the South my country Sea, especially in the Nansha Islands and the Xisha Islands[2]. According to statistical data from 1959 to 1988, it can be estimated that the number of sea turtles distributed in my country was between 16,800 and 46,300. Among them, green turtles accounted for the largest proportion, accounting for 87%, followed by hawksbill turtles, accounting for 10%, and loggerhead turtles, olive ridley turtles and leatherback turtles made up the remaining 3%[3]. According to records, among the five species of sea turtles, only green turtles, loggerhead turtles and hawksbill turtles will nest and lay eggs in my country[4]. In recent decades, with the loss of habitat and the decline of population, the nesting sites of sea turtles have been reduced to the South China Sea Islands, Taiwan and a few areas on the mainland.

Distribution of sea turtles in my country (Image source: Chan et al., 2007)

Until the 19th century, the number of sea turtles was still huge. However, today, except for a few areas where sea turtles are not threatened, the number of sea turtles in most areas is declining sharply, and many populations are even on the verge of extinction. Their survival is precarious. For many years, sea turtles have been rarely found in my country, and only occasionally captured.

What threats are facing their survival?

The main threat to the survival of sea turtles comes from human hunting. In many parts of the world, people have the bad habit of cooking turtle soup. This bad custom is particularly prevalent in the southeastern coastal areas of my country. People believe that turtle soup has high nutritional value and can cure various difficult and complicated diseases. According to incomplete statistics, from the middle of the last century to the present, about 300,000 adult sea turtles have been killed every year [5-6].

The picture of green turtles being hunted by humans in the early years (Picture from https://en.wikipedia.org/)

In addition, fishing capture, habitat degradation, marine debris, and disease are also threats to the survival of sea turtles. Shrimp trawling can cause a large number of sea turtles to drown, and approximately 150,000 sea turtles die from shrimp trawling worldwide each year [5-6]. On the one hand, human economic activities in coastal areas have seriously damaged the breeding grounds of sea turtles. On the other hand, the over-exploitation of resources such as seaweed and marine pollution caused by oil spills have seriously damaged the living environment of sea turtles. Environmental pollution increases the probability of sea turtles suffering from fibropapilloma. Fibropapilloma can grow in almost any part of the sea turtle's body, affecting the turtle's vision and movement, and ultimately leading to death.

A tumor on the head of a green sea turtle (Image from http://www.arkive.org/)

In addition to pollution and resource occupation, urban modernization also brings some unpredictable interference. In the last episode of the second season of BBC's "Planet Earth", there is a segment about a group of hawksbill turtles who mistook the city lights for moonlight and instead of crawling towards the sea, ended up wandering into the streets, where some died and some were injured. In addition, global warming has also had an impact on the survival of sea turtles that cannot be ignored.

Save the turtles

The international community has always attached great importance to the protection of sea turtle resources. It has not only established the Sea Turtle Specialist Group (MTSG), formulated international conventions, set up sea turtle websites, and regularly published journals such as the Sea Turtle Newsletter (MTN), but also established some international organizations with extensive influence and frequently held international conferences related to sea turtle protection. As early as 1995, the Species Survival Commission of the International Union for Conservation of Nature also specially formulated a programmatic document - the Global Strategy for Sea Turtle Conservation. The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) lists sea turtles in Appendix I for protection. International conventions such as the Convention on Biological Diversity, the Convention on the Conservation of Migratory Species of Wild Animals (CMS), and the Convention on Wetlands of International Importance all contain relevant provisions for the protection of sea turtles. In the Red Species List of the World Conservation Union (IUCN), hawksbill turtles and leatherback turtles are listed as critically endangered, and several other sea turtles are listed as endangered.

In response to the international action to save sea turtles, my country has promulgated laws and regulations such as the "Regulations on the Protection of Aquatic Resources", "Fisheries Law", "Wildlife Protection Law", "Management Measures for Aquatic Animal and Plant Nature Reserves" and "China Aquatic Biological Resources Conservation Action Program" since 1979, providing an important legal basis for the protection of sea turtles in my country. In 1986, the "National Key Protected Wildlife List" also evaluated five domestic sea turtles as national Class II protected animals, prohibiting illegal trade and hunting. At the same time, we vigorously carried out a census of sea turtle resources and established sea turtle protection areas.

Although many measures have been taken both internationally and domestically to protect sea turtles, the results have been minimal and the current situation of sea turtle protection is not optimistic. The main reasons are: First, people’s awareness of protection and legal awareness is weak. The public lacks awareness of wildlife protection and does not correctly understand the importance of protecting wildlife. Secondly, the survey found that many people did not even know that privately breeding and selling sea turtles is illegal, which shows that the public’s legal awareness is very weak. Second, there is a lack of effective supervision and management channels. Third, the problem of releasing sea turtles has not been completely solved. Aquariums and zoos are not the end point for the release of sea turtles. The ocean is their home. Based on the above reasons, the latest 2015 "China Vertebrate Red List" has assessed five domestic sea turtles as critically endangered [7].

Green sea turtle hatchling (Image from https://en.wikipedia.org/)

How far are we from sea turtles? Can we still see them in the ocean? Is there not enough space for a few sea turtles in the vast ocean? It is urgent to save sea turtles!

Main references:

[1]http://www.seaturtles911.org/cn/turtle/species/leatherback.htm

[2]Liang WL, Dai YR, Liu YQ, et al. 1990. The investigation of sea turtle resources in the South China Sea and the development of artificial hatching techniques for sea turtles. Report of the Conservation Stations of Southsea Turtle Resources, Gangdong Province, China, PRC.

[3]Simon Kin-Fung Chan, I-Jiunn Cheng, Ting Zhou, et al. 2007. A ComprehensiveOverview of the Population and Conservation Status of Sea Turtles in China. CHELONIAN CONSERVATION AND BIOLOGY, Volume 6, Number 2: 185-198.

[4]CHENG IJ. 1997. Studies on Chinese sea turtles. Sichuan Journal of Zoology 15 (Suppl.): 27-50 (In Chinese).

[5] Mou Jianfeng, Tao Cuihua, Ding Xiaohui, Wu Fuxing, Miao Xing, Wang Xianyan, Zhu Qian. A preliminary survey on the species and distribution of sea turtles in China’s coastal waters[J]. Chinese Journal of Applied Oceanography, 2013, 32(2): 238-294.

[6] Xia Zhongrong, Gu Hexiang, Li Pipeng. Overview of global sea turtle resources and conservation[J]. Journal of Wildlife, 2008, 29(6): 312-316.

[7]Bo Cai, Yuezhao Wang, Yueying Chen, Jiatang Li. 2015. A revised taxonomy for Chinese reptiles. Biodiversity Science, 23 (3): 365-382.