Yangzi crocodile - an animal in the genus Alligator
【Animal Profile】:
The Yangzi crocodile, Alligator sinensis (Fauvel, 1879), known as tuó in ancient times, commonly known as "earth dragon" or "pig dragon", is a small crocodile unique to China, which is listed as a national first-class key protected wild animal. Historically, Yangtze crocodiles have been widely distributed in the Yellow, Huai, Yangtze and Qiantang rivers in eastern China. With human activities and climate change, it gradually shrinks to the lower Yangtze River basin. At present, the survival of Yangzi crocodiles is very endangered, the total number of wild populations is less than 300, of which less than 100 adult individuals. Almost all wild populations are distributed in the Yangtze Crocodile National Reserve composed of five counties in southern Anhui Province, and are divided into about 20 isolated small populations. The breeding of Yangzi crocodiles under captivity conditions is very mature, and the two breeding bases in Xuanzhou, Anhui and Changxing, Zhejiang currently maintain a total of about 25,000 artificially bred Yangzi crocodiles. The loss and fragmentation of suitable habitats in the wild is the biggest threat to the Yangzi crocodile today, and the biggest obstacle to the natural recovery of its population and the introduction of captively bred body weight.
【Naming and classification】:
The Yangzi crocodile is a crocodile endemic to China. Its ancient title "鼍" has clearly appeared in oracle bones, indicating that Chinese has known and recorded Yangzi crocodiles for at least three thousand years. Since then, "鼍" has also persisted in ancient Chinese texts.
In 1879, Albert-Auguste Fauvel, a French customs worker in China and director of the Shanghai Museum, identified the Yangzi crocodile as a new species of the alligator genus of the alligator family Alligator based on four specimens collected from Wuhu, Zhenjiang and Poyang Lake, and named it Alligator sinensis.
【Behavioral characteristics】:
Body size: adult Yangzi crocodile length 1.5-2.1m, weight 30-45kg. The head is flat, the snout is prominent, the limbs are stubby and short, the forelimbs have 5 fingers, the hind limbs have 4 toes, and there are webbed crawls between the toes and swims very agilely. The tail is long and flattened, thick and powerful, which can propel the body forward in the water, and is also a weapon for attack and self-defense. Their heads are relatively large, with more grainy and banded lines on their scales, and their eyes are earthy.
Physiology: The organizational structure characteristics and physiological changes of Yangzi crocodile are compatible with living habits and living environment. For example, the developed sense of smell, vision and hearing are compatible with terrestrial predation, nesting and other behaviors, the special lung cavity structure and taste bud structure have the characteristics of adapting to aquatic life, and the seasonal changes of blood glucose concentration are compatible with the periodic alternation of the hibernation, activity or breeding period of the Yangzi crocodile.
【Behavioral habits】:
The Yangzi crocodile has superb ability to dig holes and burrows, and its head, tail and sharp toe claws are its burrowing tools. Its caves often have several openings, some in the shore beach reeds, bamboo forests, some at the bottom of the pond, ground I: there are entrances, vents. There are also side openings that adapt to various water levels. The cave is full of winding paths and criss-crosses, resembling an underground labyrinth. Perhaps it was this underground labyrinth that helped them survive the freezing ice age and cold winters, while also helping them survive from predators.
Yangzi crocodiles are quiet, often hiding in caves during the day and going out to forage at night. However, it also sometimes comes out during the day, especially on the shore and beach near the cave. It often closes its eyes tightly, crawls still and is in a semi-asleep state, giving people the illusion of slow movement. However, once it encounters an enemy or finds food, it will immediately flick its thick tail from side to side and quickly sink to the bottom to avoid the enemy or hunt down the food.
The Yangzi crocodile eats a large amount and can store a large amount of absorbed nutrients in the body, so it has a strong hunger tolerance and can survive the long hibernation period, so the Yangzi crocodile can not eat for a long time. Yangzi crocodiles have a more docile temperament and generally do not actively attack people. Like other animals, aggression tends to occur when tempered during the breeding period, but this aggression usually does not cause substantial harm to people.
Breeding: In early June, the Yangzi crocodile mates in the water and is fertilized in vivo. By around early July, female crocodiles begin to use weeds, dead branches and dirt to build round nests in suitable places for laying eggs, each laying between 10 and 30 eggs. The eggs are laid in grass and covered with weeds, while the female crocodile guards the side and incubates at natural temperatures for about 60 days. Young crocodiles emerge in September. Has a hibernation habit. The eggs are grayish-white and slightly larger than eggs. The eggs are covered with thick grass, which is the hottest season of summer, and soon, part of the nest material and thick grass rot and ferment under the hot sun, and emit heat, and the crocodile eggs use this heat and the heat energy of the sun to hatch. During the incubation period, the female crocodile often comes to guard the nest, and for about two months, after the female crocodile hears the crocodile call on the edge of the nest, she will immediately peel off the grass covering the crocodile's body to help the crocodile climb out of the nest and lead them to the pool. The body surface of the crocodile has orange-red horizontal stripes, and the color is very bright, which is obviously different from the adult crocodile.
【Distribution range】:
The Yangzi crocodile inhabits low-lying wetland environments such as lakes, swamps, and hilly ponds in plain areas. The fossil record of the Yangzi crocodile is widespread throughout eastern and central China, and even in Xinjiang and Hainan. The distribution of "shrew" recorded in ancient Chinese texts is still very extensive, mainly in the middle and lower reaches of the Yellow River, the Huai River, the middle and lower reaches of the Yangtze River and the Qiantang River basin. Since the 20th century, the distribution area has shrunk significantly and is limited to the lower reaches of the Yangtze River.
By the 50s, the distribution range of the Yangtze crocodile was further compressed to the south of the Yangtze River, Pengze, Jiangxi, Huangshan, Anhui, to Taihu Lake in Jiangsu and Zhejiang, and Yangtze crocodiles can be found in wetland environments such as lakes and streams in low terrain. After the 70s, due to agricultural expansion and continuous hunting, the distribution range of the Yangzi crocodile was further reduced to a very limited area in southern Anhui and neighboring Zhejiang. In 1979, farmers in Yin Jiabian in Changxing County, Zhejiang Province, captured 11 wild Yangzi crocodiles for captive breeding, and only 1-2 wild Yangzi crocodiles remained in the county. In 1982, the agricultural department of Anji County, Zhejiang Province found three wild Yangzi crocodiles in Xicaoxi, and no Yangzi crocodiles have been found here since. By the end of the 80s, only 5 counties and cities in southeastern Anhui Province (Nanling, Jing County, Guangde, Langxi and Xuancheng) still had stable Yangzi crocodile populations.
【Population dynamics in the wild】:
In 1981, Chinese and American scientists jointly conducted field surveys in the main distribution areas of Yangzi crocodiles in Anhui Province and estimated that the number of wild Yangzi crocodiles was 300~500;
In 1994, 77 wild individuals were found in the Yangtze Crocodile Sanctuary, and the total number of wild populations was estimated to be 664-740, but the population age structure showed that the number of juvenile individuals was small. This finding may be a significant overestimate due to bias in extrapolation methods;
From 1998 to 2003, Wang Xiaoming and Ding Youzhong of East China Normal University, in cooperation with John Thorbjarnarson, an American scholar of the International Wildlife Conservation Society (WCS), carried out long-term, large-scale and multi-method research on Yangzi crocodiles, and found that the wild population of Yangzi crocodiles was basically stable at about 120, and was divided into at least 23 small populations of different numbers and isolated from each other. Wild populations have low reproductive potential, irrational age structure, and lack of male individuals.
In 2015, a survey of 63 wild individuals was found in the Yangtze Crocodile Reserve.
Survey scope of wild populations in Anhui Yangzi Crocodile National Reserve in 2018
In 2018, 113 wild Yangzi crocodiles were found in the Yangtze Crocodile Reserve, including 63 juvenile crocodiles, with an estimated total number of 216-252.
Since 2019, the reserve has carried out large-scale artificial breeding of Yangzi crocodiles in the wild, and the wild population of Yangzi crocodiles has increased significantly. By the end of 2020, a total of 20 litters of Yangzi crocodiles released into the wild had been found during daily patrols, with a total of 366 eggs, and 215 young crocodiles had been naturally hatched.
【Protection Level】:
International Union for Conservation of Nature (IUCN): Critically endangered (CR)
Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES): Appendix I
In 1972, the Chinese government listed it as a rare animal under national protection
In 1973, the United Nations listed it as endangered and banned
In 1989, it was listed in the first level of China's List of Wild Animals under National Key Protection
【Threats】:
Wild Yangtze crocodiles are native to the vast areas of the middle and lower reaches of the Yangtze River, and due to the dense population and rapid development in the past hundred years, their habitat has been continuously developed into agricultural land such as arable land and fish ponds, so that the living space of Yangzi crocodiles has been continuously compressed, and the population has decreased sharply. From the fifties to the nineties of the last century, the Yangzi crocodile experienced rapid distribution retreat and population decline, mainly due to massive habitat loss and human predation. With the establishment of Anhui Yangzi Crocodile Reserve in the eighties, the threat of human hunting gradually decreased after the nineties, but due to the limited and highly fragmented natural habitat area, it is difficult for the Yangzi crocodile population to recover naturally, and the artificial population also lacks suitable wild release sites, and environmental pollution and loss of genetic diversity have become potential threats.
【Establishment of protected areas】:
In 1982, Anhui Province established the Yangtze Crocodile Provincial Nature Reserve, which was upgraded to a national nature reserve in 1986 to protect the Yangtze crocodile and its habitat [16]. Anhui Yangzi Crocodile National Nature Reserve is located in the combination of the low hilly area of southern Anhui and the lower reaches of the Yangtze River, spanning Guangde County, Langxi County, Xuanzhou District, Jing County and Nanling County of Wuhu City, with a total area of 18565hm2, consisting of 8 areas, namely Zhucun Piece, Gaojing Temple Piece, Yanglin Piece, Red Star Piece, Xia Du Piece, Shuangkeng Piece, Zhongqiao Piece, Changle Piece. Among them, the core area was 5188hm2, accounting for 27.94% of the total area of the protected area; The buffer zone area was 2506hm2, accounting for 13.50% of the total area of the protected area. The experimental area was 10871hm2, accounting for 58.56% of the total area of the reserve.
Captive breeding:
In 1979, Xiadu Town, Xuanzhou City, Anhui Province, established the Yangtze Crocodile Breeding Research Center, which captured 212 adult crocodiles from the wild for artificial captive breeding. In 1981, spawning and hatching under captivity conditions was achieved. In 1988, the offspring of captivity matured and participated in reproduction. Since then, the center has given birth to about 1,500 young crocodiles each year, and by 1999 the total number of Yangzi crocodiles had reached about 9,000. [14] At present, the total number of Yangzi crocodiles in the center exceeds 15,000, and the breeding rate of Yangzi crocodiles is further expanded by renting crocodiles to breed them ex situ. In 2007, 670 crocodiles were released to Nanjing Tangshan Yangzi Crocodile Breeding Base. In 2012, 200 crocodiles were released to the Wuhu Dajiang Yangzi Crocodile Breeding Base.
In 1979, farmers in Yinjia Village, Si'an Town, Changxing County, Zhejiang Province, spontaneously established the "Changxing Yinjiabian Yangzi Crocodile Sanctuary", and caught 11 wild Yangzi crocodiles into a 0.1-hectare fish pond for captive breeding. In 1988, upon the application of Changxing County, the Forestry Department of Zhejiang Province approved the establishment of the "Changxing Yinjiabian Yangtze Crocodile Reserve". In June 2002, the State Forestry Administration approved the establishment of "Zhejiang Yangzi Crocodile Seed Source Natural Breeding Research Center". In May 2007, the reserve was upgraded to a provincial nature reserve with the approval of the People's Government of Zhejiang Province, with a total area of about 130hm2 [18] . In 1984, 1997 and 2006 respectively, the breeding center realized the natural breeding of the first generation, the second generation and the third generation of Yangzi crocodiles, and the current population of Yangzi crocodiles is about 8,000.
In the 50s of the last century, a small number of Yangzi crocodiles were exchanged abroad and successfully bred in zoos in the United States and Europe to this day.
Rewilding of captive-bred individuals:
Since 2003, Xuanzhou Hongxing Reservoir, Gaojing Temple Forest Farm in Langxi County and Chongming Dongtan Wetland Park in Shanghai have successively carried out wilding and release operations of artificially bred Yangzi crocodiles.
In 2003, Anhui Yangzi Crocodile National Nature Reserve released three adult Yangzi crocodiles with strong physique and distant blood for the first time in the Red Star Protection Site with better habitat preservation. Radio-tracking monitoring for 7 months found that none of the Yangzi crocodiles released into the wild had left their habitat, and 1 litter of crocodile eggs was laid the following year. Due to the contradiction of "people and crocodiles competing for land and water," the local people have become resistant. The reintroduction strategy was adjusted to shift from the existing habitat to the newly restored habitat, and the Gaojingmiao State-owned Forest Farm in Langxi County was selected as the new reintroduction site.
Since 2002, the restoration of the Yangzi crocodile habitat has been carried out on the site of the Takai Temple Forest Farm. Taking advantage of the low-lying natural environment of the col of the forest farm, dams and ponds were built, suitable vegetation for water and land was cultivated, and aquatic animals such as fish, snails and mussels were stocked to cultivate the food chain and rebuild the wetland ecosystem. As of 2017, 46 Yangzi crocodile habitat reservoirs have been restored and 300hm2 wetlands have been restored.
In 2006, the Anhui Yangtze Crocodile Reserve released 6 Yangzi crocodiles (2 males and 4 females) on the reconstructed habitat of Gaojing Temple Forest Farm. Since then, a certain number of Yangzi crocodiles have been released in the first half of each year, ranging from 6 to 18. By 2018, a total of 105 Yangzi crocodiles had been released in the wild in the restored habitat of Gaojing Temple Forest Farm in Langxi County for 13 consecutive times.
After 2019, Anhui Yangzi Crocodile National Nature Reserve began to release artificially bred Yangzi crocodiles in the wild on a large scale in multiple protection sites. In 2019, 120 were released, 280 in 2020, 530 in the wild in 2021, and 370 in 2022. All of the Yangzi crocodiles released in 2021 were implanted with electronic chips to identify individuals, and 110 were equipped with satellite trackers to monitor their activity in the wild.
In 2007, the first phase of Shanghai Chongming Dongtan Wetland Park released 6 Yangzi crocodiles, including 3 from Zhejiang Changxing Yangzi Crocodile Natural Breeding Center, and 3 Yangzi crocodiles imported from zoos in the United States [9]. In subsequent follow-up monitoring, it was found that the introduced Yangzi crocodile had significantly increased its activity a month later, spreading to another body of water 3 km away. A month later, 2 of the box nets drilled into the river caused death by suffocation. The following year, it was found that the wild Yangzi crocodile laid a litter of eggs and carried out breeding. In 2015, the second phase of Shanghai Chongming Dongtan Wetland Park released 6 Yangzi crocodiles from the Yangtze Crocodile Breeding Center in Xuanzhou, Anhui, which belong to different lineages from the Yangzi crocodile population first introduced in 2007 to increase the genetic diversity of the local Yangzi crocodile population.
In 1992, China submitted and adopted the proposal for the registration of artificial commercial captivity of Yangtze crocodiles at the CITES Conference of the Member States.
Anhui Xuanzhou Yangzi Crocodile Breeding Center has been open to the public for more than 30 years as a popular science education base, receiving more than 150,000 visitors every year. Zhejiang Changxing Yangzi Crocodile Breeding Center is built as "China Yangzi Crocodile Village", which consists of Yangtze Crocodile Natural Breeding Mother and Child Lake, Crocodile Series Pool, Crocodile Specimen Room, Yangzi Crocodile Resort, etc., receiving about 600,000 tourists every year. They also make specimens of alligators for sale and rent them out to zoos and parks across the country.
【Ancient Texts】:
There are records of mounds as early as oracle bones.
In the "Daya Lingtai" of the Spring and Autumn Era poetry collection "Shijing", there is also a verse of "Gonggu Puffy". This means that the screams make a "bang, bang" sound like a drum.
There are records of Yangzi crocodiles in classics such as Xu Shen's "Shuowen Jiezi" in the Eastern Han Dynasty, Zhang Hua's "Natural History" in the Western Jin Dynasty, and Li Shizhen's "Compendium of Materia Medica" in the Ming Dynasty.
"Classic of Mountains and Seas, Middle Nine Classics" Minshan, the river water comes out, the northeast flows into the sea, among which there are many good shen, and there are many moos.
"Mao Shi Wen Wang Lingtai" The drums meet.
"Li Ji Yue Ling" Season and autumn moon, felling jiao to take the moon.
"Speaking of Texts" Shrew, water worm, lizard-like, long jojo, from turtle monophony.
"Kitsuka Shushu Wang Hui" will be audited. (Note: Its skin can be crowned drum)
【Species Value】:
Yangzi crocodiles are good at digging holes for nests, often nesting at reservoir embankments, often causing reservoir leakage, bringing certain harm, but for some compacted soil, it will play a loose role, which is conducive to the growth of plants; Its abandoned caves are often used by other animals. Yangzi crocodile is a carnivorous species that is at the top of the food chain and plays an important role in maintaining the balance of the food chain. The alligator feeds on fish , shrimp , molluscs and insects.
【Research Value】:
The Yangzi crocodile is an ancient reptile left over from the Mesozoic period. According to research, the bones of crocodiles have great similarities with the bones of dinosaurs, and the body surface is neatly arranged scales, indicating that crocodiles and dinosaurs have a certain kinship. Therefore, the study of Yangzi crocodile has a certain guiding effect on the study of the origin and evolution of dinosaurs and the situation of Mesozoic reptile era.