△Dugong captured in Taiwan
The last dugong sighting in mainland China was in 2008, when a dead dugong was stranded near Wenchang City, Hainan Province (pictured below). Since then, there have been no official records, so China declared dugongs functionally extinct in 2022 - which means that even if dugongs still exist in China, they are unsustainable and will become extinct in the future.
Many people are curious. Now that dugongs have reappeared in Taiwan, does it mean that this unique animal that was functionally extinct in China has won the "resurrection race"?
The simple answer is no! Even in the next few decades, it will be difficult for dugongs to win this "resurrection match"!
Dugongs are the only existing species in the family Dugongidae of the order Manatee. They have a recently extinct close relative - the famoussea cow(another species of the Dugong family), it only took 20 years for this animal to become extinct after being discovered by Westerners. It is known as the "most tragic" animal.
The order Sirenia is the only completely aquatic herbivorous mammal on earth. There are only two families in the order Sirenia - Sirenidae and Dugongidae. There are only 4 species in total - West Indian manatee, African manatee, Amazon manatee and dugong.
Among them, only the dugong is the most widely distributed, and it is also the only manatee animal living in China.
△Distribution of dugongs
Dugongs live in many places along the coasts of the Indian and Pacific Oceans. There are about 100,000 dugongs in existence. However, there are currently only two regions with relatively healthy dugong populations: Saudi Arabia and Australia. These two countries have almost all wild dugongs.
Dugong populations elsewhere are either already on the verge of extinction or are in decline.
Although official sightings of dugongs in China stopped in 2008, they have been declared functionally extinct.
But even so, it is normal to find dugongs in China, but many of them are just specious sightings by fishermen, unlike the case where they were caught in Taiwan this time with sufficient evidence.
Because dugongs are herbivores and grass has limited calories, they will migrate hundreds or even thousands of kilometers in search of food.
Wild dugongs are now distributed in the Ryukyu Islands and the Philippines, and dugongs in both areas have a very high probability of entering the coast of Taiwan to forage. It is normal for them to be accidentally caught in a net.
In addition, in the 2008 dugong stranding incident in Hainan, China (the one mentioned above), experts determined that the dugong was a dugong group from the Philippines. It just migrated here in search of food, and then it may have become alone or something, and eventually died in a foreign country.
△Flowers of the seaweed Cymodoceanodosa
Why is it so difficult to revive dugongs in China?
The food source of the entire manatee family, including dugongs, isseaweed, many people don’t know about seaweed,These are real grasses, they are the only flowering plants in the ocean, a group of angiosperms that moved from land to ocean.
After the advanced angiosperms adapted to the seawater environment, the original plants in the sea were naturally unable to compete with them, so seagrasses have achieved great success in the ocean. At present, except for Antarctica, the entire shallow sea in the world is basically occupied by seagrasses, not those native marine plants.
However, perhaps because the seawater environment cannot effectively isolate the spread of pollen, seagrasses are not diverse. There are only about 72 species of seagrasses in the world - they are closely related to each other, and the marine meadows in each region only contain one or two species of seagrasses.
△These are two types of seaweed growing in the Dugong Reserve in Hepu, Guangxi
The single species composition makes the ecology of seagrass very fragile, and it is easy to die in one piece. This is currently the case with seagrasses all over the world. They have been severely degraded due to environmental changes.
The degradation of seagrasses is one of the main reasons why manatees, including dugongs, are endangered.
Therefore, whether the dugong can be "resurrected" in China, the first thing to look at is whether the seagrass can be restored, but facts have proven that by the time China declares the dugong functionally extinct in 2022,There is only a sparse 81.7 hectares of seagrass meadow left in the dugong reserve in Hepu, Guangxi, and the amount of seagrass left is not even enough to support a dugong..
If you think about it, this is the case in protected areas, so the situation outside protected areas is probably even worse.
The degradation of seagrass is the first reason why dugongs cannot be "resurrected" in China.
△Dugong©JulienWillem
The second reason is, the number of dugongs in areas surrounding China is not optimistic. Wild dugongs in the Ryukyu Islands, Philippines, Japan, Malaysia, Sumatra, etc. are all on the verge of extinction.
If an animal becomes extinct in one place, if it wants to recover naturally, the animal must migrate from other places. However, if the populations in other places are not optimistic, the possibility of migration will be very low.
thirdDugongs are animals that have a great influence on the inheritance from generation to generation. They live in a very fixed area and almost never migrate to other places. Therefore, even if the dugong population around China is healthy, the probability of wild dugongs re-migrating to China to survive is extremely low.
A 1979 study [1] found that dugongs in different regions not only do not migrate, but there is almost no genetic exchange between their populations. The study divided the world's dugongs into five populations, and these five populations operate independently and basically do not interfere with each other.
There are two populations in China. One is from mainland China, and they form a community with dugongs from Malaysia and Sumatra. The other is from the east coast of Taiwan, and they form a community with dugongs from Japan and the Philippines.
Only dugongs in the same community will have more genetic exchanges, but the areas where their different families live are very fixed and they hardly move around.This has a lot to do with the fact that each dugong learns about the environment and survival methods from their mother, and it is difficult for them to adapt to environments outside their native habitat.
Dugong's foraging migration usually occurs in small groups, and appearing alone usually means that it may be alone, soThe situation of the dugong caught in Taiwan may not be optimistic. If it is left alone, it may not be able to live independently..
On the other hand, it would be very difficult for dugongs themselves to recover from functional extinction!
Dugongs have a very weak reproductive capacity, and their lifespan is only 50 to 70 years. However, their generation interval is 25-26 years, and they only give birth to one calf per litter, with a lactation period of up to three years, which means that it is difficult for them to restore their population.
actually,For animals like dugongs that still exist, there is a simple and effective way to recover from disappearance in one area, and that is to directly reintroduce them from other areas.
However, China is probably far from ready to welcome dugongs at the moment, and they themselves are not the kind of animals that can be declared functionally extinct today and reintroduced tomorrow.
refer to:
[1].https://www.icrwhale.org/pdf/SC031133-141.pdf