A recent study by scientists from the Chinese Academy of Sciences and the Zoological Society of London, published in the journal Royal Society Open Science, said that in recent decades, China's mermaid prototype "dugong" has experienced rapid population collapse. It is currently "functionally extinct" in China. Someone asked: Is a dugong a manatee? It is often said on the Internet that dugongs are dugongs and manatees are manatees, not a class of animals. In fact, this statement is biased. This article will take you to know the dugong and its "relatives".
Dugong belongs to the order Manatee, a class of aquatic mammals that feed mainly on plants, and there are 2 families in the order Manatee: Trichechidae and Dugongidae.
There are 3 extant species in the family Manatee family: the Amazon manatee, the American manatee, and the African manatee.
There is 1 extant species in the dugong family: the dugong.
Distribution map of manatees: The green is the American manatee, the red is the Amazon manatee, the orange is the African manatee, the blue is the dugong, and the yellow circle is the Hydrodamalis gigas of the dugong family, which was extinct in the 18th century
Image credit: B Kimmel
How is the distinction between the manatee family and the dugong family?
The most obvious difference between manatees and dugongs is their tails. The manatee family, which includes the Amazon manatee, the West African manatee, and the American manatee, has a round oar-shaped tail, which is like the "tuan fan" used by ancient court ladies to cool off. The tail of the dugong family resembles the tail fin of a cetacean and is "V" shaped.
There is a clear difference in the tails of the manatee family and the dugong family
Image source: Marine Sciences, Sun Yat-sen University
With one exception, the Slavic manatee belongs to the dugong family and has a "V" shaped tail. It can be described as a "giant" in the sea, with a body length of up to 9 meters, far more than all manatees and dugongs today. However, the Stella manatee became extinct in the 18th century due to human overfishing.
The german zoologist Georg Wilhelm Strauss measures the body data of a Stella manatee in 1742
Image credit: Stejneger
01
Dugong dugon
Dugongs are found in a much wider range than the manatee family, and at their peak, dugongs were almost all visible from the western Pacific to the Indian Ocean, along the 140,000 kilometers of coastline north and south of the equator, and the rest of their distribution spanned more than 30 countries around the world.
Pictured here is a dugong foraging on the seabed of Marsa Alam, Egypt
Image source: Alberto Scarani
Dugongs like to eat tropical or subtropical seaweed in shallow waters, and when eating, they are accustomed to uprooting the whole seaweed, and if they can't pull it off, the dugong will eat their leaves or stems.
Above: A dugong swimming with a fish near The Island of Lamen in Vanuatu Image: Simon Naunton
Below: A dugong mother and son swimming together in the waters off East Timor Image source: Nick Hobgood
Dugongs are shy by nature and do not like to approach humans.
Most dugongs can hold their breath underwater for 2 and a half minutes, and some dugongs can even hold their breath for 6-8 minutes, and they can dive into waters close to 40 meters deep. Dugong pups often interact with their mothers, such as physically touching each other, and sometimes stick out their tails to stroke their mothers for comfort.
【Population Status】
At present, the world's dugongs are mainly distributed in the northern coastal areas of Australia, and their numbers have declined sharply due to human hunting and habitat destruction.
In the 1990s, according to aeronautical survey statistics, there were an estimated 100,000 dugongs in the world in the 1990s, and Australia alone accounted for 85,000.
In 2000, dugongs were listed as vulnerable (VU) species by the IUCN. Most countries and territories in the world today have established legal protection for dugongs, and only some of the islands in northern Australia and the indigenous people of western Papua New Guinea are allowed to hunt dugongs.
On the mainland, before the 1970s, stranded dugongs were found in coastal waters in Guangdong, Guangxi, Hainan and other places. With economic developments, such as the development of seafood aquaculture in dugong-infested areas, dugongs have declined sharply under threats such as bycatch by fishing boats, illegal killings, and reduced food sources (degradation of seagrass habitats). At the end of 1999, a dead dugong was found in the waters near the Guangxi North Sea, which was the last individual dugong to die found around the Hepu Dugong National Nature Reserve in mainland China. In 2008, the dugong found in Dongfang City, Hainan Province, was the last record of the discovery of dugong in mainland China.
02
Amazon manatee (Trichechus inunguis)
Amazon manatees are found only in the main rivers and lakes of the Amazon Basin in South America, and can be found in countries such as Brazil, Peru, Colombia and Ecuador.
The activity of the Amazon manatee changes with the seasons of the Amazon basin. During the flood-rich season, they appear in flooded forests or meadows; During the dry season in July and August, water levels drop and some Amazon manatees are forced to stay deep in the large lakes, where they usually stay until the end of the dry season in March.
Some scientists believe that during this time, they hardly eat, rely on the fat stored in the body and the low metabolic rate to maintain life, they can live for seven or eight months in the absence of food or less food.
The body of the Amazon manatee is scattered with fine brown or gray hairs. The picture shows an Amazon manatee undergoing rehabilitation at the Brazilian Institute of Environmental and Renewable Natural Resources on the island of Marajo, Brazil
Image source: KCO3
Image credit: Anselmo-d'Affonseca
The Amazon manatee has a white patch on its chest. They have no remaining claws on their flippers, an important feature that distinguishes them from other manatees. The Amazon manatee is also the smallest in the Manatee Corey, with adult Amazon manatees ranging in length from 1.62 to 2.3 meters.
The picture shows an Amazon manatee that is about to surface for ventilation Image source: Dirk Meyer
The Amazon manatee lives almost entirely underwater, but also surfaces for ventilation at regular intervals. Captive Amazon manatees have a recorded maximum stay underwater for 14 minutes.
【Population Status】
The main threat of the Amazon manatee is illegal hunting. The main motivation for local indigenous people to hunt Amazon manatees is their own livelihood.
The fat and skin of the Amazon manatee are used by locals to cook food and herbs, and the meat is sold to farmers markets for money.
Between 1935 and 1954, about 140,000 Amazon manatees were killed. By 1977, the population of Amazon manatees was estimated to be about 10,000 head.
While many countries have enacted laws prohibiting the killing of Amazon manatees, hunting continues. Between 2004 and 2015, illegal hunters in several regions of Brazil hunted and killed more than 650 Amazon manatees in order to obtain seafood.
In 2008, the IUCN Red List listed the Amazon manatee as a vulnerable (VU) species.
The cubs of the Amazon manatee found in a tributary of the Cabin River in Brazil in 2015 Image: Goianésia do Pará
03
Trichechus manatus
The American manatee, also known as the West Indian manatee, is found in shallower waters along the Atlantic coast and in some rivers of the Americas.
The American manatee has sparse hair, gray skin, and an average body length of about 2.7-3.2 meters, making it the largest of the surviving manatees. Depending on the living waters, the American manatee can be divided into 2 subspecies:
1. Florida manatee subspecies (Trichechus manatus latirostris)
2. Trichechus manatus manatus
In the Holofer Canal at the Merritt Island National Wildlife Refuge in Florida, two Florida subspecies of American manatees basking in the sun
Image credit: Gordon E. Robertson
1. Florida manatee subspecies (Trichechus manatus latirostris)
Florida manatees are found off the coast of Florida in the United States, west to Texas and north to Massachusetts.
Every summer, Florida manatees can reach western Texas and northern Massachusetts, but in the winter, they congregate on the coast near Florida because only the warmth of the water here can help them survive the cold weather.
Florida manatees in the Crystal River, Florida
Image credit: Cynthia Taylor
【Population Status】
The Florida manatee was listed as a vulnerable (VU) species by the IUCN in October 2007. They are mainly subjected to physical injuries (such as collisions) from human vessels, loss of habitat in warm waters, extremely high mortality during pregnancy, and red tides.
In 1997, M. Marmontel, S. Humphrey and other scholars predicted the survival capacity of Florida manatees, and they believed that if the living environment of Florida manatees continues to improve and countries do not introduce strong protection regulations, then the probability of extinction of Florida manatees in the next 1,000 years is as high as 44%.
An aerial survey of Florida manatees from 2015 to 2016 showed that there were about 8,800 Florida manatees in Florida (data revised in December 2018).
South Florida Museum's Manatee Transit Sign
Image credit: Bigmacthealmanac
2. Trichechus manatus manatus
The Andrean manatee is sparsely distributed in the Caribbean, north to Mexico, south to the waters near Brazil, and their "mysterious" figures can be seen sporadically.
However, the most important habitat of the Andrean manatee is the coast of Belize, where the combination of rivers, lakes, lagoons and shallow seas has created a composite ecosystem of seagrass, mangroves and coral reefs, providing a variety of environments for them to eat, drink, and raise their babies.
Usually, they mostly stay in estuarine environments between oceans or brackish water.
(a) A female Antillean manatee captured near Changinora, Panama, in 1964;
(b) A female Antilles from Bocas del Toro, Panama, 1964;
(c) A male Antillean manatee weighing more than 360 kg by Bocas del Toro in Panama in 1964;
(d) The Antillean manatee who died in 1982 under the locks of a ship near Pedro Miguel Island
Image credit: Hector M. Guzman et al
【Population Status】
The Andreas manatee was listed as vulnerable (VU) by the IUCN in October 2007 along with the Florida manatee.
The Antillean manatee is mainly threatened by habitat fragmentation and illegal hunting. In fact, due to the relatively turbid and poor illumination of the habitat of the Andrean manatee, the effect of the previous methods of investigating the Population of Andrean Manatees (such as aviation and sonar) is not very obvious, so the population data of the Andrean Manatee is very small.
In 2016, Alves and other scholars studied the population of Antillean manatees in Brazil and concluded that there are about 485-2221 potential head in Brazil. In 2017, the U.S. Fish and Wildlife Service concluded that there are currently more than 6,700 Antillean manatees.
Scholars witnessed an Air-breathing Andrean manatee in the Cararay River in the Andean region
Image source: Juan et al
04
African manatee (Trichechus senegalensis)
The African manatee, also known as the West African manatee, is distributed in the waters of the west coast of Africa and extends inward into some of the inland rivers of West Africa, such as the Niger River.
Compared with the Freshwater-loving Amazon manatee and the Ocean-loving American Manatee, the West African Manatee is more "easy-going", from the intersection of brackish water to brackish water to freshwater, such as oceans, estuaries, bays, lagoons, rivers, lakes, reservoirs and other waters, can become their paradise.
During the day, African manatees doze off in shallow water 1-2 meters deep.
In countries such as Sierra Leone, whenever the flood season comes in June and July, African manatees migrate upstream along rivers until they encounter shallow water or waterfalls and cannot move on. This is because floods reduce their food sources.
Pictured here are West African manatees at the COEX Aquarium in Seoul, South Korea
Image credit: Mehdi Sadak 2ème compte
West African manatees are generally grey and covered with transparent hairs.
However, because some algae and other small organisms often grow on the body of the African manatee, its body sometimes appears brown or green.
Researchers at the American Museum of Natural History photographed African manatees on land in the last century.
The body length of the African manatee can reach 4.5 meters. They generally move slowly, but when frightened by predators, they can move at speeds of about 30 kilometers per hour.
【Population Status】
African manatees are threatened on many fronts.
First, illegal hunting: Poachers hunt them and get their flesh, fat, bones, and skin in exchange for huge fortunes. In Nigeria, Cameroon and other countries, African manatees are illegally sold as pets to zoos and aquariums. People in countries such as Mali and Chad also use the oil of African manatees to treat diseases such as ear infections, rheumatism and skin diseases.
African manatees that stray into fishing nets
Image credit: inaturalist
Second, urban and agricultural development: the increase in damming projects has reduced the habitat of African manatees and caused physical harm to them, such as the accidental death of African manatees in turbines, water inlet valves, and fishing nets.
The population of African manatees has been unclear. In a 1998 eyewitness survey conducted by Monica Silva of the University of the Azores in three regions of Guinea-Bissau, the results of which reported that only 256 African manatees were sighted between 1990 and 1998. On the IUCN Red List of Threatened Species, revised in 2015, African manatees have been classified as vulnerable (VU) species.