Imagine what you would get if you added a dolphin's tail and two elephant tusks to a seal's body, and then gave it a cow's habit of grazing leisurely.
That's right, will get a dugong. This adorable marine mammal perfectly embodies all of the wonderful features of all these creatures.
1. Introduction
The word Dugong is derived from the Malay word "duyung", which means mermaid or lady of the sea. They are also often called Sea Cows, Sea Pigs and Sea Camels.
Dugongs are large mammals that live in warm coastal waters. Because of its eating habits, which mainly feed on seaweed, and cattle are mainly herbivores, people affectionately call them manatees.
This particular species looks a lot like manatees, reflecting the fact that both species are relatives of elephants.
The only way to visually tell the sex of a dugong is to look at its fangs – male dugongs develop fangs when they are sexually mature, while females have no visible fangs.
Dugong is the only surviving species of the dugong family and one of four species of manatees. This makes dugongs really very special and rare.
This huge mammal can grow up to 3 meters long and weigh up to 300 kilograms, resembling an overweight dolphin.
Their noses have a special design – nostrils grow on top of the nose. The nostrils open for breathing when returning to the surface and close when diving into the water. They cannot hold their breath for a long time, about 6 minutes per dive.
Dugongs have a strong sense of hearing, smell and touch, but their visual abilities are somewhat weak.
2. Physical characteristics
Dugongs are huge marine mammals that can grow up to 3 meters long and weigh up to 300 kilograms.
They are born with creamy skin and turn dark grey or brownish grey as adults. The thick skin surface is smooth with only sparse hairs on it.
The dugong has a round head, a large mouth and small eyes. The well-developed upper lip forms a U-shaped cushion with double ridges and large, stiff bristles. The front fin, which is about 45 cm in size, resembles a rowing pulp. Their tails are much like dolphins, and when their tails swing up and down, they can be pushed to swim in the water. All dugongs have fangs , but only adult males can see them.
Female dugongs have thymic glands that breastfeed their offspring, which resemble human glands, which may be why ancient sailors imagined dugongs as mermaids.
Dugongs' nostrils grow on top of the nose, and these nostrils have special "valves" that close underwater and open again when they return to the surface to breathe. Dugongs can dive for about 6 minutes at a time.
The heavy skeleton helps the dugong dive easily and stay there to enjoy the delicious seaweed. But seaweed is difficult to digest, so dugongs evolved intestines up to 30 meters long.
3, Dugong vs Manatee
Both dugongs and manatees belong to the order Manatees. Four species of manatees currently live: 3 species of manatees and 1 species of dugongs.
Both dugongs and manatees are relatives of elephants and are slow-moving herbivores. But that concludes the similarities between the two.
Dugongs live in shallow water reserves, while manatees live in swampy areas of the Gulf of Mexico and the Caribbean Sea. Dugongs are strictly marine mammals, unlike manatees which can be found in fresh water.
Dugong
manatee
Despite their similarity in appearance, there are many different bodies in dugongs and manatees:
(1) Manatees are slightly larger than dugongs.
(2) The slurry tail of the manatee is long and horizontal, with a leaf on the tail that swings up and down when the manatee swims. The tail of the dugong is similar to that of a dolphin, with a pointed protrusion.
(3) Manatees have nails, while dugongs do not.
(4) The nostrils of dugongs grow above the nose, while those of manatees do not.
(5) The dugong's mouth is more pronounced, the nose is like an elephant's trunk, while the manatee's nose is shorter.
(6) The upper lip of the dugong is not separated, while the manatee is separated.
(7) Male dugongs have tusks similar to ivory, while manatees do not, only molars.
The difference between the two is not only physical, but also in the reproductive cycle: female manatees reach sexual maturity at about 3 years of age and give birth every 2 to 3 years; Female dugongs reach sexual maturity at the age of 10 and give birth every 3 to 5 years.
4. Habitat
Dugongs are strictly marine mammals. They are found in the warm waters of the east coast of Africa and the western Pacific Ocean. They are usually concentrated in shallow protected bays, wide mangrove waterways, and leeward areas on island coasts.
Seagrass is a food source for dugongs. As a result, their habitat range mainly corresponds to the two families of seagrasses in the family Hydrocharitaceae and Potamogetonaceae.
Dugongs inhabit waters at depths of about 10 meters, although they are known to operate in waters more than 10 kilometers from the coast and dive at depths of 37 meters.
Dugongs sometimes descend into the deep sea to eat deep-sea seagrass, but shallow areas are preferred to reduce the risk of predation and facilitate reproduction. However, in winter, dugongs go to the deep sea in search of warm shelter, as the water near the coast can become very cold.
It is understood that dugongs currently inhabit 37 countries, of which Australia has the largest number. In Chinese mainland, Vietnam and Cambodia, dugongs are found in very small numbers; There are an estimated 4,000 dugongs in the Red Sea; There are an estimated 7,500 in the Persian Gulf; The populations of dugongs on the coasts of Mozambique and East Africa are relatively small, 120 and 500, respectively; In the northern Indian Ocean, dugongs are found in the Andaman and Nicobar Islands, the Paok Strait (between India and Sri Lanka) and the northeast coast of Sri Lanka; An isolated dugong population inhabits Marine National Park (located in Kuchi Bay, India).
Small amounts of dugong are also found along the coasts of Japan, Taiwan and the Philippines; Some have been found in the western region of the Gulf of Thailand; Very small amounts of dugong appear in the Straits of Johor; Dugongs were once also found around the Maldives and Racardiff, but they have become extinct in these areas; The same is true of the Mediterranean, where dugongs once flourished.
5. Eating habits and predators
Dugongs are large herbivores that feed on seaweeds. Their low metabolic rate and extremely slow movement allow them to survive on an entirely herbivorous diet.
There is evidence that dugongs feed on a wide variety of seagrasses and algae. Although dugongs are herbivores, they also occasionally eat some sea squirts, jellyfish, and shellfish. Studies have shown that dugongs in Australia are omnivores, feeding on polychaetes (marine link worms/millipedes). But dugongs prefer to eat seagrass with relatively low fiber content and high nitrogen content, and seagrass is highly nutritious, so it is not necessary to eat a lot of food.
Dugongs search for food from morning to night, and they even go to the deep sea to feed. When foraging along the seabed, they wiggle their pectoral fins to move.
They have limited visual abilities and therefore need to rely on a strong sense of smell to identify edible plants. In addition, their keen sense of touch helps them feel their surroundings.
When eating, dugongs uproot the whole plant, shake it to remove the sand on it, and then eat the whole plant with roots. Before the feast, they collect the plants and stack them in one place.
Dugongs move slowly, making them vulnerable to predators such as killer whales, sharks, and crocodiles. They can only rely on their huge size, huge skeleton, thick skin, and rapidly clotting blood to defend themselves. However, these predators mainly attack young dugongs, and humans do the most harm to dugongs.
6. Reproduction and life cycle
Dugongs reach sexual maturity quite late compared to other mammals. Dugongs will reach sexual maturity at the age of 6~17. Female dugongs reach sexual maturity around the age of 6 and usually give birth to their first cubs between the ages of 6~17. Males usually reach sexual maturity between 6~12 years old.
The main reason to distinguish whether a male dugong is an adult is whether he has fangs. Fangs are the result of high levels of testosterone. There is evidence that fertility declines in older males.
Dugongs have a very low reproductive rate - reproduction every 2~7 years, one reason may be that the gestation period is as long as 13~15 months.
Males are always waiting for adult females because they can breed all year round.
Dugong mating behavior may vary slightly depending on the habitat. For example, in Australia, male dugongs compete fiercely with each other in order to compete for the mating rights of females. Males establish a territory and wait for females to visit. Competing males can become very violent and will use protruding fangs to fight each intruder in order to protect their territory. During males competing against each other, female dugongs are ridden on the back multiple times by multiple males. This guarantees conception rates and makes them a polygamous species.
After a long gestation period - 13~15 months - the cubs are born. The pups are about 1.2m long and weigh 30kg. These pups are vulnerable to predators, so they will always follow and ride on their mother's back.
Mothers spend 18 months nursing their pups. Also, the female dugong, as the primary caregiver, is responsible for raising the cubs. During weaning, a strong bond is established between the mother and the pup.
Female dugongs generally live with their offspring for 6 years. In the first 2 years, the mother will teach the child how to eat seaweed. For the next 5 years, they eat together and strengthen their bond with each other. When sexual maturity is reached, the pups leave their mothers.
Dugongs can live for a long time – 70 years or more. The age of the fangs can be determined by the growth layer on them.
Dugongs are susceptible to infectious diseases and parasites. But keeping them in captivity is unrealistic because their special diet is expensive and difficult to obtain, and the dugong pups are weaned for up to 18 months.
7. Behavior and communication
Dugongs are social animals, and a group usually has 2~200 dugongs. Groups of only two individuals usually consist of a mother and her cubs. Groups of 200 dugongs are rare because it requires huge amounts of seaweed to feed them.
Dugongs are semi-nomadic species and often require long migrations to find suitable seagrass beds. They may also live in the same area for the rest of their lives if they are not necessary. Whether to migrate to "greener pastures" depends on the quality and quantity of seagrass available. If the seagrass in their habitat is depleted, they are forced to migrate to another location.
These huge mammals are very shy and try to stay away from any sources of interference. Therefore, they are difficult to spot in murky waters. Because dugongs avoid contact with humans, studying their behavior is a difficult task.
Because they are social animals, communication is crucial for them. Sound and vision are the two main forms of communication – sound is usually used for long-distance communication, while vision is only used for close communication. Dugongs communicate with whistles, chirps, barks, and squeaks. Every sound has a special purpose. For example, chirping indicates that they are foraging; Barking when patrolling territory indicates their offensive behavior. In addition, they have a highly developed auditory system, as they need to distinguish the frequencies of different sounds.
Dugongs use their sense of smell and bristles to forage. They are covered with sensory bristles all over their bodies to enhance their tactile abilities. These bristles can detect vibrations around them to aid in foraging. In addition, mothers and cubs also have physical contact through these bristles.
8. Protection status
Over the years, dugong populations have declined dramatically, making them an endangered species. Dugong pups are preyed upon by predators such as sharks and killer whales, while adult dugongs are hunted by humans – meat and oil. They are trapped in fishing nets and often die from lack of oxygen. They are also frequently hit by boats and, most importantly, their natural habitat is destroyed – the oceans are increasingly polluted, resulting in severe damage to seagrass beds, the main source of food for dugongs, which directly threaten the survival of dugongs.
It is difficult to increase the number of dugongs, as mentioned above, their reproductive rate is very low. Moreover, it is unrealistic to feed them safely in captivity – weaning for up to 18 months.
For the currently surviving dugongs, their natural habitat should be protected and the impact of humans on them reduced. In Australia, 16 dugong reserves have been established. These protected areas are rich in seagrass, providing an ideal habitat for dugongs. These areas also include shallow water areas suitable for breeding.
9. Cultural significance
Dugongs are of great cultural significance. They are an integral part of the people living in the World Heritage areas of the Great Barrier Reef. Dugong as a food source enhances Aboriginal and Torres Strait Islander cultures. Hunting dugongs and sharing dugong meat is a continuation of its ancient traditional culture.
The dugong is also a symbol of the ancient culture of the Okinawans, so it is included in Japan's Cultural Property Protection Law as a creature of cultural significance.
In Thailand, dugongs are believed to have magical properties, and many items are made from different body parts of dugongs; In India, dugong meat is considered an aphrodisiac; In Papua New Guinea, dugongs are a symbol of strength; In Kenya, dugong body parts are used as medicine, food, and decorations.
10. Evolutionary history
Both dugongs and manatees belong to the order Sirenia. The fossil record suggests that these marine mammals date back as early as 50 million years ago.
Tethytheria is thought to be a connecting part of elephant evolution and belongs to Paenungulata, which includes the order Nepatee. Tethytheria was originally a land animal and later became aquatic and semi-aquatic. The reason for their return to aquatic life is most likely related to food.
Recent molecular evidence suggests a close evolutionary relationship between Tethytheria, elephants, and dugongs.
Original English text:
https://www.aboutanimals.com/mammal/dugong/