The turtles that appeared in groups on the river bank are not actually that many...

Not long ago, a piece of news like this became a hot topic: some citizens saw a large number of soft-shelled turtles appearing on the shore of a river in Wuhan, constantly popping their heads up to breathe, and some even crawled directly onto the shore. Soft-shelled turtles are a common aquatic product in our country. Many people think that there are a lot of soft-shelled turtles because they are so common. Do you think there are really a lot of them?

Source: Weibo screenshot

01 A "decision" that goes against our ancestors

"Soft-shell turtle" is a general term for the family Testudinidae under the order Testudinata and the suborder Testudinata. Turtle is actually a type of turtle that is highly specialized and adapted to aquatic life.

A turtle's shell is a hard bone box formed by the fusion of its own spine, ribs and subcutaneous bone plates (called intradermal osteogenesis , which also exists under the skin of crocodiles and some lizards). It is covered with a thick stratum corneum, which can provide protection for the slow-moving turtle when facing natural enemies.

Chinese soft-shell turtle (Source: Wikipedia)

In order to gain greater maneuverability underwater and to chase agile fish and shrimp or to drill into narrow crevices in rocks, the turtle made a "decision that went against its ancestors": it highly streamlined its tortoise shell for self-defense - not only did the carapace become flat and thin, the stratum corneum on the surface was also highly degraded, covered with a layer of soft and elastic skin, and formed a "skirt" at the edge of the carapace, and the plastron was almost completely degraded, leaving only a few bone fragments buried under the skin.

Don't think that a soft-shelled turtle is weak and can be bullied just because it looks flabby! The family Trionycii is not only agile, but also has the longest neck in the suborder of the Cynomorium and a strong bite force. I believe that some readers have had the painful experience of teasing a soft-shelled turtle when they were young, and it suddenly popped out its head and neck and bit it and wouldn't let go.

02 The "two-end" breathing method of the reverse Tiangang

Like other reptiles, turtles mainly breathe through lungs. However, in order to increase the time they can spend underwater, they have also evolved a "secret weapon": two sac-like organs called anal sacs on both sides of their rectum, which are densely covered with capillaries and can directly absorb dissolved oxygen in the water like the gills of fish. The anal sacs are particularly important for breathing when turtles bury themselves in the mud and sand at the bottom of the water to ambush passing fish or hibernate underwater.

In the hot summer, the rising water temperature will not only increase the metabolic rate of the cold-blooded turtles, thereby consuming more oxygen, but also cause the dissolved oxygen content in the water to decrease. This forces the turtles to surface more frequently and rely on their lungs to absorb enough oxygen for their bodies.

03 When turtles emerge collectively, do you think there are a lot of them?

Experts believe that the turtles that appeared in the Wuhan section of the river belong to the Chinese soft-shelled turtle, a native species. These Chinese soft-shelled turtles may be wild individuals that were forced to migrate due to rising water levels and the loss of suitable shallows for survival, but it is not ruled out that they are artificially released or escaped farmed turtles. Their collective "appearance" on the river bank has triggered our thinking about the protection of wild Chinese soft-shelled turtles.

There is a popular saying among the public that wild Chinese soft-shelled turtles are "very nutritious" and "strong in sexual function", but there is actually no evidence that wild Chinese soft-shelled turtles differ greatly in nutritional content from farmed Chinese soft-shelled turtles, and the taste of farmed soft-shelled turtles is almost indistinguishable from that of wild Chinese soft-shelled turtles. As for the saying that wild soft-shelled turtles can strengthen sexual function, this is also unfounded.

Due to the over-hunting of wild Chinese soft-shelled turtles over the years, coupled with habitat destruction (such as water pollution, draining and filling wetlands, cement hardening of river and lake banks that have deprived turtles of their spawning grounds, etc.), the wild Chinese soft-shelled turtle population is currently in decline and is listed as a vulnerable species on the IUCN Red List, the same level as the giant panda [Note]. From the perspective of protecting wild Chinese soft-shelled turtle resources and the ecological protection of the Yangtze River Basin, large-scale fishing of Chinese soft-shelled turtles is indeed an act that should not be encouraged.

[Note] The threat level of wild populations of species evaluated by IUCN does not necessarily correspond to the level of classification in my country's Wildlife Protection Law. For example, the giant panda is a first-class protected animal in my country, while the Chinese soft-shell turtle is not a key protected animal. Although the protection levels in China are not the same, they are at the same level on the IUCN Red List. Therefore, this also draws our attention, and wild Chinese soft-shell turtles also need urgent protection.

04 Releasing farmed soft-shelled turtles as a “remedy”? Very unreliable!

Since catching large numbers of wild Chinese soft-shelled turtles will be detrimental to their population resources and the ecological balance of the entire Yangtze River Basin, can releasing farmed soft-shelled turtles into the wild restore wild Chinese soft-shelled turtle resources?

In the past, the academic community once thought that there was only one species of Chinese soft-shelled turtle in all parts of the country, but newer studies have separated out 6 new species from the Chinese soft-shelled turtle [Note: Some scholars also believe that the stone-flaked soft-shelled turtle or the Huangshan horseshoe soft-shelled turtle should not be independently classified as a new species] , including:

Pelodiscus axenaria , distributed in Hunan Province

Small softshell turtle ( Pelodiscus parviformis ) distributed in Hunan and Guangxi

The Northeastern softshell turtle ( Pelodiscus maackii ) is found in Russia, the Korean Peninsula, Japan, and Northeast China.

Pelodiscus shipian , native to Anhui and Jiangxi provinces

Huangshan horseshoe turtle ( Pelodiscus huangshanensis ) is native to Huangshan, Anhui Province.

Spotted softshell turtle ( Pelodiscus variegatus ) from Hainan

They are placed in the genus Pelodiscus together with the Chinese soft-shell turtle ( Pelodiscus sinensis ). In addition, there are probably new species in the genus Pelodiscus that we have not yet discovered.

Northeastern soft-shelled turtle (Source: Wikipedia)

Spotted softshell turtle (Source: Wikipedia)

In order to breed Chinese soft-shelled turtles that grow fast, have strong reproductive capacity, strong resistance to adversity, and high meat yield, farmers often hybridize members of the genus Chinese soft-shelled turtle from different origins, or even from different species, and artificially select and breed the hybrid offspring, such as the " yellow sand soft-shelled turtle ", a common breeding strain in Hunan Province, and the " Japanese soft-shelled turtle " produced by hybridizing and breeding the Chinese soft-shelled turtle and the Northeast soft-shelled turtle.

When these farmed turtles are released into the wild, they may hybridize with wild Chinese soft-shelled turtles and thus contaminate the gene pool of wild populations , posing a great threat to their survival. Indiscriminately releasing large numbers of turtles and other aquatic animals may also lead to the death of these farmed animals due to their inability to adapt to the environment. After their corpses rot, they will pollute the water and spread diseases.

Florida softshell turtle (Source: Wikipedia)

Some other farmed turtles, such as the Florida soft-shell turtle ( Apalone ferox ) native to North America, are undoubted alien species. They look similar to native soft-shell turtles and are difficult for non-professionals to identify. If released into the wild, they may compete with native turtles for food and other survival resources, or even prey on native aquatic animals, becoming an invasive species that harms the local ecological environment.

Author: Hu Kai, science research instructor, CCTV-9 documentary channel science consultant

Reviewer: Ran Hao, Distinguished Researcher, Key Laboratory of Ecology and Environmental Protection of Rare and Endangered Animals and Plants, Ministry of Education (Guangxi Normal University)

Produced by: Science Popularization China