Dugong

The dugong (/ˈd(j)uːɡɒŋ/; Dugong dugon) is a marine mammal. It is one of four living species of the order Sirenia, which also includes three species of manatees. It is the only living representative of the once-diverse family Dugongidae; its closest modern relative, Steller's sea cow (Hydrodamalis gigas), was hunted to extinction in the 18th century.

The dugong lives in the waters of about 40 countries and territories in the Indo-West Pacific. It depends mostly on seagrass communities for food, so it lives near coasts where there are seagrass meadows. Big groups of dugongs are often found in wide, shallow, safe areas like bays, mangrove channels, and near large islands. The northern waters of Australia between Shark Bay and Moreton Bay are thought to be where most dugongs live today.

Dugongs have a body shape that helps them swim, with no back fin or back legs. Their front legs are like paddles. They can be told apart from manatees by their tail, which looks like a dolphin's tail. They also have a special skull and teeth, and their noses point downward to help them eat seagrass on the sea floor.

People have hunted dugongs for thousands of years for their meat and oil, and this still matters culturally in places like northern Australia and the Pacific Islands. Today, dugongs are in danger because of human activities like fishing, loss of their seagrass homes, and hunting. They live a long time—up to 70 years or more—and have few babies, making it hard for their numbers to grow.

Evolution

See also: Evolution of sirenians

Dugongs belong to a group of animals called Sirenia, which includes modern "sea cows" like manatees and dugongs, as well as their extinct relatives. These are the only herbivorous marine mammals that live completely underwater. Scientists believe sirenians have been around for about 50 million years, starting from the early Eocene period until today. They were more diverse during the Oligocene and Miocene periods but their numbers decreased because of changes in climate, ocean conditions, and human actions.

Etymology and taxonomy

The word "dugong" comes from a language called Visayan, probably from Cebuano. A French scientist named Georges-Louis Leclerc, Comte de Buffon, first used the name in 1765 after hearing about the animal from the island of Leyte in the Philippines. The name does not mean "lady of the sea" as some people think.

The dugong, Dugong dugon, is the only living species in its family, Dugongidae. It is one of four living species in the Sirenia order, which also includes manatees. Dugongs are more closely related to elephants than to other marine mammals. Their closest known relative, Steller's sea cow, went extinct in the 18th century.

Anatomy and morphology

The dugong has a large, cylinder-shaped body that gets narrower at both ends. It is born with pale, smooth skin that darkens as it grows older, often turning brownish or dark grey. This colour change can happen because algae grow on its skin.

Adult dugongs are usually about 3 metres (10 feet) long and can weigh between 250 and 900 kilograms (550 to 1,980 pounds). The biggest dugong ever found was 4.06 metres (13 feet 4 inches) long and weighed 1,016 kilograms (2,240 pounds). This huge dugong was found near the coast of Saurashtra in western India. Female dugongs are usually a bit bigger than males.

Dugongs have very few hairs on their bodies, mostly around their mouths. They have a special, horseshoe-shaped upper lip that helps them forage for food. Their tails and flippers look similar to those of dolphins, with the tail moving up and down to swim and twisting to turn. Dugongs do not have nails on their flippers. Their brains are small, weighing up to 300 grams (11 ounces), and they have limited vision but very good hearing. They can close their nostrils with valves to keep water out. Female dugongs have teats behind their flippers for nursing their young. Males and females look almost the same, with the main difference being the position of certain body parts. Dugongs have long lungs and kidneys, which help them live in salty water. If hurt, their blood clots quickly to stop bleeding.

The dugong's skull is special, with a strong, down-turned part in males. They have between 57 and 60 bones in their spine. Unlike manatees, dugongs do not constantly grow new teeth. Male dugongs grow two tusks during puberty, while females may grow tusks that sometimes emerge later in life. Dugongs have a specific set of teeth, and their bones are very heavy, which may help them stay slightly below the water's surface.

Distribution and habitat

Dugongs live in warm coastal waters from the western Pacific Ocean to the eastern coast of Africa, covering about 140,000 kilometres (87,000 mi) of coastline near the equator. They prefer shallow, protected bays with seagrass beds, which they eat. Today, dugongs are found in the waters of 37 countries and territories, but their numbers are decreasing. They have disappeared from places like Hong Kong, Mauritius, and Taiwan.

Australia has the largest population of dugongs, especially in Shark Bay and the Gulf of Carpentaria. The Persian Gulf has the second-largest population, but numbers have dropped by about 25% since 1950 due to poaching, oil spills, and nets. In East Africa and South Asia, populations are very small and may disappear soon. In Southeast Asia and the West Pacific, dugongs are found in places like Vietnam, Thailand, and the Philippines, but their numbers are low due to fishing and loss of seagrass habitats. In the Northern Pacific, small populations exist around the Ryukyu islands and Okinawa, but they are endangered. Dugongs once lived in the Mediterranean sea, but they are now extinct there.

Ecology and life history

Dugongs can live a long time, with the oldest one known being 73 years old. They don't have many natural enemies, but young dugongs can be threatened by animals like crocodiles, killer whales, and sharks. They can also get sick from infections and diseases, which can sometimes cause death.

Dugongs are usually alone or in pairs because the seagrass areas where they live can't support big groups. They are shy and stay away from humans, so scientists don't know much about their behavior. They can stay underwater for up to six minutes and usually breathe every two and a half minutes. They can dive deep, up to 39 metres, but most of the time they stay in shallower water. Dugongs talk to each other using chirps, whistles, and other sounds underwater. Mothers and their babies stay very close to each other.

Dugongs move around a lot looking for food but usually stay in the same general area. They travel to find better seagrass to eat and can remember where good feeding spots are. Sometimes they travel very far, even over the ocean, to find food.

Feeding

Dugongs eat mainly seagrass, which is why they are called "sea cows." They eat the whole plant, including the roots, but sometimes just the leaves if they can't get the roots. They might also eat algae or small sea animals when seagrass is hard to find. They prefer seagrass that is low in fiber and high in nutrients. By eating, they help certain types of seagrass grow better. Dugongs use their sense of smell and touch to find food, and they use their lips to dig up plants from the sand.

Reproduction and parental care

It takes a while for dugongs to grow up—they reach maturity between eight and eighteen years old. Females usually have a baby only a few times in their lives and take good care of their young. After carrying a baby for about 13 to 15 months, a female gives birth in shallow water. The newborn baby is already about 1.2 metres long and stays close to its mother for about 14 to 18 months while it learns to eat seagrass.

Importance to humans

Dugongs have been important to people for thousands of years. They were hunted for their meat, oil, skin, and bones, and have even inspired stories of mermaids. In some cultures, dugongs are considered special and killing them is seen as bad luck. However, in other places, dugong meat and parts have been highly valued and hunted almost to extinction.

In many areas, dugongs are important to local traditions and culture. Some people believe that dugongs were once human or part-human, and they are protected in certain regions. In others, dugongs are still hunted for food and other uses. Today, efforts are being made to protect dugongs and their habitats.

Conservation

Dugong numbers have gone down in recent times. To keep their population stable, adult dugongs cannot die at a rate higher than 5% each year. Humans can take only 1–2% of female dugongs without causing the population to shrink, especially in places where food is scarce. Even with the best care, dugong populations grow very slowly, making them easy to harm from human actions. Because they live in shallow waters, dugongs face many dangers from people.

The IUCN Red List says the dugong is vulnerable, and international rules help protect them. Many countries have laws to guard dugongs, though some places still struggle to enforce these rules. Efforts to protect dugongs include setting aside special areas and working together across countries.