The dolphin that swam with its dead cub for more than a month was named Lin

On August 18, 2023, we found a strange Chinese white dolphin while we were out at sea for investigation on the east coast of Leizhou Peninsula in Zhanjiang City. It stayed on the sea for a long time and did not seem to have any intention of entering the water. This is very abnormal. Dolphins breathe with their lungs and need to repeatedly enter and exit the water to complete breathing. Chinese white dolphins usually dive for 3-5 minutes after a complete breath.

As we got closer, we found that it was carrying a dead calf on its back , or in other words, a piece of skin and several intestines. The calf was already highly decomposed, with bones, muscles and most of its organs missing, and only a layer of fat connected its relatively tough digestive tract. The adult dolphin floated on the surface just to stay with her calf.

A mother pig carrying her dead baby｜Lin Wenzhi

The next day, we saw her again about 30 kilometers away. It is not easy to swim with a child on your back, and you have to prevent the child from being washed away by the sea at any time. Judging from the degree of decay of the baby dolphin, the mother has been carrying the child on her back for more than a month without sleep . Normally, we will not intervene in the behavior of animals, but considering that the sea conditions will deteriorate in the future, we decided to take the baby dolphin away from its mother, hoping to help the mother dolphin resume normal life. The incomplete remains of the baby dolphin have also become the saddest record in our white dolphin database.

During the surveys over the past few years, we have encountered such heartbreaking scenes several times; but the slightly comforting thing is that we often see other individuals accompanying these bereaved mothers. When the mother pig is unable to carry her child, other pigs will even take over her task , just like what Mencius said, "Love your own children, and also other people's children."

The baby dolphin was already dead, but the mother kept pushing it out of the water, not wanting it to sink to the bottom｜Lin Wenzhi

During the years I have been with white dolphins, I have gradually realized that they are not only highly intelligent, but also have deep emotional connections with their companions, just like humans. For example, the Chinese white dolphin population in the eastern part of Leizhou Peninsula, which we have tracked for 11 years, has formed its own "village" - villagers in the same village have a harmonious relationship, but there is little communication between different villages, and even two villages have ignored each other for several years.

Pink dolphin brings good luck

Many friends’ knowledge about the Chinese white dolphin may come from the message “Forward this pink dolphin and you will have good luck for the whole year.”

Chinese white dolphin jumps out of the water, the pink one is the mother, the gray one is the baby｜Chen Shenglan

Pink is not the most common skin color of Chinese white dolphins - they are born black, gradually fade as they grow up, until they become a unique and bright white when they grow up , hence the name "white dolphin". However, just like human skin becomes congested after exercise, adult individuals jumping around in the sea look closer to pink.

There are not many animals named after "China", and the Chinese white dolphin is one of them. The whale species in China's coastal waters are not very abundant. The brightly colored Chinese white dolphin, which prefers to stay close to the shore, is the easiest whale to observe . How close to the shore? Sometimes you can see the Chinese white dolphin while walking along the coast or driving on the Hong Kong-Zhuhai-Macao Bridge.

This shows how "nearshore" this nearshore species is.

But the probability of this "sometimes" is a bit small - the Chinese white dolphin populations currently known in China are all in a state of decline , and some populations are already in danger. In some areas, there are only a few dolphins left, and among the white dolphin populations that are still relatively large:

There are only 12 tigers left in the Shantou population, and all the newborns since 2010 have died[1];

The Xiamen population was less than 60 in 2015[2];

The population in western Taiwan had fallen to less than 80 individuals by 2010[3];

There are only about 100 remaining in the Beibu Gulf population in Guangxi [4], but there are still reports that the total number is between 500 and 600.

Only the Pan-Pearl River Estuary population (a metapopulation that includes multiple subpopulations such as Lingdingyang, Hong Kong, and Jiangmen) and the Zhanjiang Leizhou Peninsula eastern population have a slight advantage in total number, with the former exceeding 2,000 and the latter close to 500[5]. However, the Lingdingyang population has decreased by 45% in the past decade[6]. In comparison, the Zhanjiang population is the healthiest population in China - but it is still declining at a rate of 2.9% per year.

Unlike most other small dolphins, Chinese white dolphins are highly loyal to their region and have lived in the same place for generations . No individual exchange has ever been found in the known populations in China, and genetic studies have also shown that the genes of populations in different places are unique [8, 9]. If a population in a certain area becomes extinct, white dolphins will no longer appear there - this hypothesis is not far-fetched. Ningde, Zhangzhou and Shantou are likely to witness the disappearance of white dolphins in the next 20 years.

Ancient village in the ocean

In our research, we found that white dolphins are not only highly loyal to their regions, but even dolphins in the same area have their own activity areas.

We spent 11 years tracking and analyzing the white dolphin population in Zhanjiang. It turned out that they can be divided into four main communities and one free unit consisting of only 7 individuals . We named each community: the largest community with the healthiest members was named "Lin's Community" (this was my mentor's strong request, you can guess what his last name is...), which occupies the southern waters of Leizhou Bay; the other three communities were named "Li's Community", "Chen's Community" and "Liu's Community" from north to south; the free unit was named Mino (meaning minority).

The community structure of the Chinese white dolphin "Zhanjiang Branch". Judging from the scope of activities, the white dolphin carrying the stillborn calf mentioned at the beginning of the article is a member of the Lam Tsuen

Among the four communities, the Chen community overlaps with the other communities, while the remaining three communities each occupy one side. Members of each community occasionally visit each other, but the Lin and Li communities, which occupy the north and south ends, ignore each other and have never had any communication between their members . This is like a human village - each village occupies a piece of land, and the relationship within the village is closer than between villages; when transportation is inconvenient, there is less communication or even no communication between villages that are geographically far away.

But unlike humans, there are no geographical barriers such as mountains and rivers between dolphin "villages", and they can easily cross dozens of kilometers. The white dolphin mother mentioned at the beginning of the article crossed 30 kilometers in one day. The Li and Lin families are only less than 50 kilometers apart, so the reason they do not visit each other can only be summarized as " can go, but don't want to go " - as for why they don't want to go, we are not clear yet.

This refreshes our understanding of Chinese white dolphin society. Previous studies on the Hong Kong and Xiamen populations suggested that the relationships between white dolphins were loose, short-lived, and fluid[12]; although there was a close connection within the Taiwan population, researchers believed that this might be due to the small size of the population. This time, in the Zhanjiang branch of the Chinese white dolphin population, which has as many as 500 dolphins, we found that they had a stable, long-lasting, and close relationship.

Chen's community travel together｜Lin Wenzhi

Complex social structures are not uncommon among cetaceans, which are typical social animals. For example, within the sperm whale family, adult females will help each other take care of their children. Like sperm whales, killer whales are also typical matriarchal societies, where mothers lead their offspring and grandchildren to live together. They have their own unique social culture that is passed down from generation to generation in terms of food selection and hunting techniques.

According to our tracking of Chinese white dolphins, they also have similar social cultures. For example, as mentioned at the beginning, when a mother dolphin carries and mourns her cub, other individuals in the same village will take over the responsibility; the fact that the Li family and the Lin family do not interact with each other may also be the social culture of the two villages. The relationship between dolphins can affect genetic structure, disease transmission, individual adaptability and many other aspects . Studying their social relationships can help us better understand these neighbors at sea.

The strong preference of different communities for geographical locations also makes our research more directly useful - as long as you take out a photo of a Chinese white dolphin in Zhanjiang, we can roughly guess where you took it and tell you which village it is from .

One of the most recognizable dolphins in the Zhanjiang branch. Its dorsal fin was cut by fishing line, so I named it Huajuan. It is from the Chen family and often moves in the northern waters of Leizhou Bay｜Lin Wenzhi

Another easy-to-recognize dolphin, numbered 0528, also seems to have been strangled by a fishing line, which fell off after aging, but its body will not heal again; it is a member of the Lin family, so it is basically impossible to see it in Zhanjiang Bay (also known as Guangzhou Bay), Naozhou Island or the northern waters of Leizhou Bay｜Lin Wenzhi

Different villages, different fates

During our trip, we recorded 23 white dolphins that had been attacked by large sharks, some of which were attacked multiple times. Among them, 17 were members of the Chen family . Is it because Chen members are tastier or because they are closer to sharks?

In fact, there is a deep ditch at the entrance of Chen Village. Sharks wandering in the deep sea may come in along the ditch to look for food, forcing the dolphins in Chen Village to start a "shark escape". There are shallow beaches surrounding Li Village and Lin Village, so sharks cannot pass through; Liu Village is blocked by Chen Village. As for the six victim dolphins that are not members of Chen Village, they probably wandered around Chen Village out of boredom and were bitten...

The dolphin numbered 0170 is the one that survived at least two shark attacks. It is the Chencun dolphin.

In addition to defending against natural enemies, dolphins also need to withstand additional pressure from humans.

My mentor is from Zhanjiang. When he passed by his hometown on his way to sea, he said that the village where he lived when he was a child had been developed into a business district. Development activities can develop the local economy and allow people to live a better life; but few people notice that these activities have also brought far-reaching impacts to our maritime neighbors :

The development and utilization of sea areas will occupy the white dolphins' near-shore living space; the carelessly discarded garbage will be washed into their homes by rainwater, and fishing garbage such as hemp ropes and fishing nets will cut their dorsal fins and strangle their necks; hungry dolphins may accidentally eat plastic garbage floating in the water, causing digestive tract obstruction and death.

In July 2022, we saw the little dolphin in the picture above. At that time, its head was accidentally caught in the fishing rope loop and it couldn't get out. In June 2023, we saw it again. At this time, the hemp rope had been deeply tied to its neck. The picture was taken in Jiangmen, but there are many such dolphins in other areas. | Chen Shenglan, Lin Wenzhi

The forms and intensities of economic activities in each region are different, so the pressures faced by white dolphins in different regions are also different. The dolphins living around large cities not only suffer from ship collisions and noise pollution caused by more developed freight, but also permanently lose their habitats due to land reclamation for urban expansion, and have to endure the noise and industrial pollution caused by land reclamation construction.

The two pictures below show the same dolphin "Hope", whose tail fin was broken by the propeller. Although it was later taken up for treatment, it was eventually euthanized due to its severe injuries (vertebral fracture and necrosis, nerve tissue infection) | The pictures are from Lam Man-Chi, Hong Kong Swire Institute of Marine Science, and Hong Kong Ocean Park Conservation Foundation

Fortunately, a large area of ​​the Leizhou Peninsula in Zhanjiang City has been designated as protected farmland, and the precious natural pristine coastline, mudflats and offshore waters are protected by the ecological protection red line. Therefore, compared with other areas, the "country dolphins" in Zhanjiang are still living a good life . By observing the dolphins' bodies through drones, we also found that the Zhanjiang white dolphins are "happy and fat", and their nutritional level is the best among the populations in Guangdong and Guangxi (possibly in the whole country) [10].

However, even within the population, the survival pressures faced by white dolphins in different villages in Zhanjiang are very different . For example, the area around Zhanjiang Bay has developed into the most densely populated residential area in Zhanjiang, and industry and shipping have also flourished in recent years. In contrast, although Leizhou Bay is surrounded by the ecological red line, the areas where Chencun and Liucun are located have successively laid cages and oyster piles for aquaculture in recent years; only Lincun is protected by the ecological red line on a large scale - a long section of natural and original coastline is preserved here, and the Zhanjiang Leizhou Bay Chinese White Dolphin Nature Reserve is also established here. In our subsequent analysis, we also found that the Lin community is the healthiest group of all Chinese white dolphins in China, and it is also the only group of Chinese white dolphins in China that can continue stably under the status quo.

Can they wait for their good luck?

Last August, within a few weeks, we recorded seven newborn dolphins in Zhanjiang, but four of them were already dead bodies on their mothers’ backs when we saw them . We confirmed the identity of the mothers and learned that Licun lost a new life, Chencun lost two and saved one, and Lincun lost one and saved two. But even after passing the birth barrier, the baby dolphins are still very fragile before the weaning period of 2-3 years old.

The healthy newborn dolphin has not yet learned to breathe freely, and can only lift its head up, with its body covered with folds. You should have discovered that its mother is Huajuan｜Lin Wenzhi

This group of Chinese white dolphins in Zhanjiang migrated and settled in this bay about 30,000 years ago[11]. In the last few thousand years, humans have become their new neighbors. But for thousands of years, most humans living here did not know that within 20 nautical miles extending eastward from the Leizhou Peninsula, the Chinese white dolphin society has also been changing from generation to generation , accompanying us in building civilization, slash-and-burn agriculture, going through the feudal era, achieving the industrial revolution, and moving towards modernization. The same is true in other regions.

As time goes by, human society is no longer the same as it was thousands of years ago, but the society of white dolphins is still almost as primitive as it was thousands of years ago . Compared with humans, dolphins are more stubborn and inflexible, because their mothers live here, and they will not leave even if the environment is not as good as before.

As things change rapidly and we stride forward, should we also take some time to look back at our old companions cruising in the bay?

Local residents on the shore watching dolphins｜Lin Wenzhi

References

This article is based on Chen, S., Lin, W., Liu, B., Serres, A., Lin, M., Liu, M., & Li, S. (2025) Long-lasting social bonds of a habitat-structured delphinid social system. Animal Behaviour, 219: 123025.

Other references are:

[1] Lin W, Zheng R, Xu S, et al. Indo-Pacific humpback dolphins face extirpation in Shantou waters [J]. Regional Studies in Marine Science, 2024, 77: 103641.

[2] Zeng Q, Lin W, Dai Y, et al. Modeling demographic parameters of an edge-of-range population of Indo-Pacific humpback dolphin in Xiamen Bay, China [J]. Regional Studies in Marine Science, 2020, 40: 101462.

[3] Wang JY, Riehl KN, Klein MN, et al. Chapter Four - Biology and Conservation of the Taiwanese Humpback Dolphin, Sousa chinensis taiwanensis [M]//JEFFERSON TA, CURRY B E. Advances in Marine Biology. Academic Press. 2016: 91-117.

[4] Lin W, Zheng R, Liu B, et al. Low Survivals and Rapid Demographic Decline of a Threatened Estuarine Delphinid [J]. Frontiers in Marine Science, 2022, 9: 782680.

[5] Lin W, Chen S, Liu B, et al. Survival and population size of the Indo-Pacific humpback dolphins off the eastern Leizhou Peninsula [J]. Marine Mammal Science, 2024: e13156.

[6] Lin W, Karczmarski L, Chan SCY, et al. Population parameters and heterogeneity in survival rates of Indo-Pacific humpback dolphins in a heavily urbanized coastal region of southeast China: implications for conservation [J]. Frontiers in Marine Science, 2024, 11.

[7] Zhang P, Zhao Y, Li C, et al. An Indo-Pacific Humpback Dolphin Genome Reveals Insights into Chromosome Evolution and the Demography of a Vulnerable Species [J]. iScience, 2020, 23(10).

[8] Zhao L, Sakornwimon W, Lin W, et al. Early divergence and differential population histories of the Indo-Pacific humpback dolphin in the Pacific and Indian Oceans [J]. Integrative zoology, 2021, 16.

[9] Gowans S, Würsig B, Karczmarski L. The social structure and strategies of delphinids: Predictions based on an ecological framework [J]. Advances in Marine Biology, 2007, 53: 195-294.

[10] Serres A, Lin W, Liu B, et al. Skinny dolphins: Can poor body condition explain population decline in Indo-Pacific humpback dolphins (Sousa chinensis)? [J]. Science of The Total Environment, 2024, 917: 170401.

[11] Zhao L, Sakornwimon W, Lin W, et al. Reply to “Misuse of molecular tools results in misleading dates for the ancestor of the Indo-Pacific humpback dolphin” by Chen [J]. Marine Mammal Science, 2022, 38: 395-9.

Author: Chen Shenglan

Editor: Mai Mai

Title image source: Lin Wenzhi

This article comes from GuokrNature (ID: GuokrNature)

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