Dugong facts for kids
The dugong, Dugong dugon, is a large mammal that lives its whole life in the sea. They are sometimes called "sea cows" because they eat a lot of sea grass. Dugongs live in warm, shallow areas where sea grass grows. This includes the north coast of Australia, and parts of the Indian Ocean and the Pacific Ocean.
Dugongs are more closely related to elephants than to other sea animals. Their closest relative in the water is the manatee. Manatees live in fresh water in America and West Africa.
A dugong can grow to about 3 m (10 ft) long. They can weigh as much as 400 kg (882 lb). Dugongs only come to the surface to breathe. Unlike seals, they never come onto land. A baby dugong is called a calf. It drinks milk from its mother until it is about two years old. A dugong becomes an adult between 9 and 17 years old. They can live for up to 70 years. Dugongs are grey to brown in color. They have a tail with flukes, like a whale, and flippers. They do not have a dorsal fin like a shark. They have a wide flat nose, small eyes, and small ears.
Dugongs are migratory animals, but they move very slowly. Studies show that many dugongs travel less than 15 km (9 mi). However, some have traveled as far as 560 km (348 mi). Scientists think dugongs move long distances for several reasons. They might be looking for food if cyclones or floods affect the seagrass. Males might follow females or look for their own space. If the water gets cold (less than 17 degrees Celsius), they will move to warmer areas.
Because of their size, the only animals that attack dugongs are sharks, the Saltwater Crocodile, and killer whales.
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About the Dugong's Body
A dugong's body is large and shaped like a cylinder. It gets narrower at both ends. Their skin is thick and smooth. It is pale cream when they are born, but turns brownish-grey as they get older. The color can also change if algae grows on their skin. Dugongs have a few short hairs on their body. These hairs help them feel their surroundings. The hairs are thickest around their mouth. Their mouth has a large, horseshoe-shaped upper lip. This strong lip helps the dugong find and eat food.
The dugong's tail flukes and flippers are like those of dolphins. They move their tail flukes up and down to swim forward. They can twist their tail to turn. Their front limbs are paddle-like flippers. These help them turn and slow down. Dugongs do not have nails on their flippers. Their flippers are only about 15% of their body length. The tail has deep notches.
A dugong's brain weighs about 300 g (11 oz). This is only about 0.1% of their body weight. Dugongs have very small eyes, so they don't see well. But they have excellent hearing for certain sounds. Their ears do not have outer flaps and are on the sides of their head. Their nostrils are on top of their head and can close with valves. Male and female dugongs look almost the same. Their lungs are very long, reaching almost to their kidneys. Their kidneys are also long to help them live in saltwater. If a dugong gets hurt, its blood will clot quickly.
The dugong's skull is special. It is large with a sharply downward-curved upper jaw. The spine has between 57 and 60 vertebrae. Unlike manatees, a dugong's teeth do not keep growing back. Male dugongs have two incisors (tusks) that appear during puberty. Female tusks grow but usually do not come out until later in life. The number of growth rings in a tusk shows a dugong's age. Their cheek teeth also move forward as they age. Like other sirenians, dugongs have very dense bones. These heavy bones help them stay slightly below the water's surface.
Adult dugongs rarely grow longer than 3 metres (9.8 ft). A dugong this long might weigh around 420 kilograms (926 lb). Most adults weigh between 250 kilograms (551 lb) and 900 kilograms (1,984 lb). The largest dugong ever recorded was 4.06 metres (13.32 ft) long and weighed 1,016 kilograms (2,240 lb). It was found off the Saurashtra coast of west India. Females tend to be larger than males.
Where Dugongs Live
Dugongs live in warm coastal waters. Their range stretches from the western Pacific Ocean to the eastern coast of Africa. This covers about 140,000 kilometres (86,992 mi) of coastline. They are found between 26° and 27° degrees north and south of the equator. Historically, they lived wherever certain types of seagrass grew. The full size of their past range is not known. Today, dugongs are found in the waters of 37 countries. The number of dugongs recorded is often lower than the actual number because surveys are hard to do.
Despite this, the dugong population is believed to be shrinking. There has been a 20% decline worldwide in the last 90 years. They have disappeared from places like Hong Kong, Mauritius, and Taiwan. They are also gone from parts of Cambodia, Japan, the Philippines, and Vietnam. More disappearances are likely.
Dugongs usually live in warm coastal waters. They gather in large numbers in wide, shallow, protected bays. The dugong is the only mammal that lives only in the sea and eats only plants. Manatees use fresh water sometimes. Dugongs can live in brackish water (a mix of fresh and salt water) found in coastal wetlands. Many are also found in wide, shallow mangrove channels. They also live around the sheltered sides of large islands where seagrass beds are common.
They are usually found at a depth of about 10 m (33 ft). But in areas where the seabed stays shallow, dugongs can travel more than 10 kilometres (6 mi) from shore. They can go as deep as 37 metres (121 ft), where deepwater seagrasses grow. They use different habitats for different activities. Shallow waters are used for giving birth, which helps protect the calves from predators. Deeper waters might offer a warm place to hide from cooler waters near the shore in winter.
Dugongs Around the World
In the 1960s, groups of up to 500 dugongs were seen off East Africa. Now, populations there are very small, often 50 or less. They might become extinct in these areas. The eastern Red Sea has hundreds of dugongs, and similar numbers are thought to be on the western side. In the 1980s, there might have been as many as 4,000 dugongs in the Red Sea. The Persian Gulf has the second-largest dugong population in the world, with about 7,500 animals. However, recent studies show big declines there.
Dugong numbers in Madagascar are not well known, but they have likely dropped a lot. In Mozambique, most populations are very small. The largest group (about 120) is at Bazaruto Island. In Tanzania, more dugongs have been seen around the Mafia Island Marine Park. In the Seychelles, dugongs were thought to be extinct until a few were found around the Aldabra Atoll.
A small, separate group lives in the Marine National Park, Gulf of Kutch in western India. This group is far from other dugong populations. Past populations in the Maldives and Laccadive Islands are likely gone. A group lives between India and Sri Lanka in the Gulf of Mannar Marine National Park and the Palk Strait, but their numbers are very low.
A small population lives along the southern coast of China. Efforts are being made to protect them. In Vietnam, dugongs are mostly found in Kiên Giang and Bà Rịa–Vũng Tàu provinces. Con Dao Island is now the only place in Vietnam where dugongs are seen regularly. In Thailand, dugongs are found in 6 provinces along the Andaman Sea. Very few are in the Gulf of Thailand. Small numbers are thought to live in the Straits of Johor. The waters around Borneo also have a small population. All islands of the Philippines likely once had dugongs. Populations exist around the Solomon Islands and New Caledonia, reaching to Vanuatu. A very isolated group lives around the islands of Palau.
The smallest and northernmost dugong population lives around the Ryukyu islands in Japan. An endangered group of 50 or fewer dugongs survives around Okinawa. New sightings of a mother and calf in 2017 suggest they might be breeding there.
Australia has the largest dugong population. It stretches from Shark Bay in Western Australia to Moreton Bay in Queensland. Shark Bay's population is stable with over 10,000 dugongs. Over 20,000 dugongs live in the gulf of Carpentaria. More than 25,000 live in the Torres Strait. The Great Barrier Reef is an important feeding area, with about 10,000 dugongs. Large bays in Queensland also provide important homes for dugongs.
It is believed that dugongs once lived in the Mediterranean. This group might have been related to the Red Sea population. However, this Mediterranean population was never very large.
Dugong Life and Habits
Dugongs live a long time. The oldest one recorded was 73 years old. They have few natural enemies. Crocodiles, killer whales, and sharks can be a threat to young dugongs. Dugongs can get many infections and diseases. About 30% of dugong deaths in Queensland since 1996 are thought to be from disease.
Dugongs are social animals, but they are usually found alone or in pairs. This is because seagrass beds cannot support very large groups. Sometimes, hundreds of dugongs gather, but only for a short time. Dugongs are shy and do not come close to humans, so little is known about their behavior. They can hold their breath for six minutes, but usually only for about two and a half minutes. They have been seen resting on their tail with their heads above water to breathe. They can dive to a maximum depth of 39 metres (128 ft). Most of their lives are spent no deeper than 10 metres (33 ft).
Dugongs communicate using chirps, whistles, barks, and other sounds underwater. Different sounds might have different meanings. They don't see well, so visual communication is limited. Mothers and calves stay in almost constant physical contact. Calves sometimes touch their mothers with their flippers for comfort.
Dugongs are semi-nomadic. They often travel long distances to find food, but they stay within a certain area their whole life. Large groups often move together. These movements are thought to be caused by changes in how much seagrass is available. Their memory helps them return to specific places after long journeys. Daily movement is affected by the tides. In areas with big tides, dugongs travel with the tide to reach shallower feeding areas. In colder areas, dugongs travel to warmer water during winter. Sometimes, individual dugongs make very long trips over deep ocean waters. One was seen as far south as Sydney. Although they are sea creatures, dugongs have been known to travel up creeks. One was caught 15 kilometres (9.3 mi) up a creek near Cooktown.
What Dugongs Eat
Dugongs, like other sirenians, are called "sea cows" because they mainly eat sea-grass. When they eat, they swallow the whole plant, including the roots. If they cannot, they will eat just the leaves. Dugongs eat many different types of seagrass. They will also eat algae if seagrass is scarce. Although they are almost completely herbivorous (plant-eaters), they sometimes eat invertebrates like jellyfish, sea squirts, and shellfish. In some areas, dugongs actively look for large invertebrates.
Most dugongs do not feed in very thick seagrass areas. They prefer places where the seagrass is more spread out. Other things like protein levels and how well the seagrass can grow back also matter. The best seagrass for them is low in fiber, high in nitrogen, and easy to digest. Dugongs may even change the types of seagrass that grow in an area by their feeding. They might look for deeper seagrass. Feeding trails have been seen as deep as 33 metres (108 ft). Dugongs have been seen feeding as deep as 37 metres (121 ft). Dugongs are relatively slow, swimming at about 10 kilometres per hour (6.2 mph). When they feed on the seabed, they walk on their front fins.
Dugong feeding can help certain types of seagrass grow. These are the low-fiber, high-nitrogen types that dugongs prefer. Dugongs may also prefer to eat younger, less fibrous seagrass plants.
Because they don't see well, dugongs often use their sense of smell to find food. They also have a strong sense of touch. They feel their surroundings with their long, sensitive bristles. They will dig up a whole plant and shake off the sand before eating it. They have been known to gather a pile of plants in one spot before eating them. Their flexible and strong upper lip is used to dig out the plants. This leaves grooves in the sand where they have fed.
How Dugongs Reproduce
A dugong becomes an adult between eight and eighteen years old. This is older than most other mammals. Females know a male is mature when his tusks appear. The age when a female first gives birth is debated, but it is usually between six and seventeen years. Even though dugongs can live for 50 years or more, females only give birth a few times in their lives. They spend a lot of time caring for their young. The time between births is unclear, with estimates from 2.4 to 7 years.
Females give birth after a 13–15 month gestation (pregnancy). They usually have only one calf. Birth happens in very shallow water, sometimes almost on the shore. As soon as the calf is born, the mother pushes it to the surface to take a breath. Newborns are already 1.2 metres (4 ft) long and weigh around 30 kilograms (66 lb). Once born, they stay close to their mothers, possibly to make swimming easier. The calf drinks milk for 14–18 months, but it starts eating seagrass soon after birth. A calf will only leave its mother once it is grown up.
Dugongs and Humans
Dugongs have been hunted by humans for a long time. People hunted them for their meat, oil, skin, and bones. They are often thought to be the inspiration for mermaids. People around the world have developed cultures around dugong hunting. In some areas, they are still very important animals. A growing ecotourism industry around dugongs has helped some countries economically.
There is a 5,000-year-old cave painting of a dugong in Tambun Cave, Ipoh, Malaysia. This painting was found in 1959. In the past, dugongs were sometimes shown in special collections of rare objects. They were also presented as Fiji mermaids in shows.
Dugong meat and oil have traditionally been very valuable foods for Aboriginal Australians and Torres Strait Islanders. Some Aboriginal Australians see dugongs as part of their identity. Dugongs have also been part of legends in Kenya, where they are called the "Queen of the Sea." Their body parts are used for food, medicine, and decorations. In the Gulf states, dugongs were a food source, and their tusks were used for sword handles. Dugong oil is important for preserving wooden boats in the Gulf of Kutch in India. Dugong ribs were used for carvings in Japan. In Southern China, dugongs were traditionally seen as a "miraculous fish," and it was bad luck to catch them. However, hunting for food increased later. In the Philippines, dugongs are thought to bring bad luck, and parts of them are used to protect against evil spirits. In parts of Thailand, it is believed that dugong tears make a powerful love potion. In parts of Indonesia, they are thought to be women who have come back to life. In Papua New Guinea, they are a symbol of strength.
Some believe that dugong hides were used as coverings for the Old Testament worship tent called the Tabernacle.
Protecting Dugongs
Dugong numbers have gone down recently. For a dugong population to stay healthy, 95% of adults must survive each year. Humans can only kill 1–2% of females without harming the population. This number is even lower if there isn't enough food for calves. Even in the best conditions, a population is unlikely to grow more than 5% a year. This makes dugongs very sensitive to too much hunting. The fact that they live in shallow waters puts them at risk from human activities. Research on dugongs and human impact has been limited, mostly in Australia. In many countries, dugong numbers have never been counted. So, it's hard to know how their populations are changing. The only long-term data comes from the coast of Queensland, Australia. A major study in 2002 found that dugongs were declining and possibly extinct in one-third of their range. Their status was unknown in another half.
Threats from Human Activity
Even though dugongs are protected by law in many countries, their numbers are still declining. The main reasons are human activities like hunting, habitat damage, and deaths from fishing. Getting caught in fishing nets has caused many deaths, but exact numbers are not known. Most problems with large-scale fishing happen in deeper waters where there are fewer dugongs. Local fishing is the main risk in shallower waters. Since dugongs cannot stay underwater for a very long time, they are very likely to die if they get tangled. Shark nets used to cause many deaths, but they have been replaced with baited hooks in most areas. Hunting has also been a problem, but in most places, dugongs are no longer hunted, except by some local communities. In places like northern Australia, hunting is still the biggest threat to dugongs.
Boat strikes have been a problem for manatees, but we don't know how much they affect dugongs. More boat traffic increases the danger, especially in shallow waters. Ecotourism has grown in some countries, but its effects are not fully known. It has caused problems in areas like Hainan due to environmental damage. Modern farming and more land clearing have also had an impact. Much of the coastline where dugongs live is becoming more industrialized, with more people. Dugongs collect heavy metals in their bodies over their lives, more than other sea mammals. The effects of this are not known.
Oil spills are a danger to dugongs in some areas, as is land reclamation (creating new land from the sea). In Okinawa, the small dugong population is threatened by United States military activity. Plans to build a military base near the Henoko reef could cause noise pollution, chemical pollution, and soil erosion. Some people in Okinawa have fought these plans in court.
Environmental Damage
If dugongs do not get enough to eat, they might give birth later and have fewer young. Food shortages can happen for many reasons. These include losing their habitat, seagrass dying or becoming unhealthy, and human activity disturbing their feeding. Sewage, detergents, heavy metals, salty water, herbicides, and other waste products all harm seagrass meadows. Human activities like mining, trawling (fishing with a net), dredging (clearing the seabed), land reclamation, and boat propellers also increase sedimentation. Sediment smothers seagrass and blocks light from reaching it. This is the biggest negative factor for seagrass.
One of the dugong's favorite seagrass species, Halophila ovalis, dies quickly without enough light. It can die completely in 30 days. Extreme weather like cyclones and floods can destroy hundreds of square kilometers of seagrass meadows. They can also wash dugongs ashore. It can take over ten years for seagrass meadows to recover. Most protection efforts involve limiting activities like trawling in seagrass areas. There is less action on pollution coming from land. In some areas, water salinity (saltiness) increases due to wastewater. It is not known how much salinity seagrass can handle.
Dugong habitat in the Oura Bay area of Henoko, Okinawa, Japan, is currently threatened by land reclamation. This is being done by the Japanese Government to build a US Marine base. Construction is expected to seriously damage the dugong population's habitat. It could even lead to them disappearing from that area.
Dugongs in Captivity
The Australian state of Queensland has sixteen dugong protection parks. Some areas are preservation zones where even Aboriginal Peoples are not allowed to hunt. Capturing dugongs for research has caused only one or two deaths. Dugongs are expensive to keep in captivity. This is because mothers and calves spend a long time together. Also, the seagrass dugongs eat cannot be grown in an aquarium. Only one orphaned calf has ever been successfully kept in captivity.
Worldwide, only four dugongs are held in captivity. A female from the Philippines lives at Toba Aquarium in Toba, Mie, Japan. A male also lived there until he died in 2011. The second lives in Sea World Indonesia. It was rescued from a fisherman's net and treated. The last two—a male and a female—are kept at Sydney Aquarium. They have been there since they were young.
Images for kids
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Dugong skeleton displayed at Philippine National Museum
See also
In Spanish: Dugongo para niños
