Dugong

## Description

The dugong (; 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 is the only sirenian in its range, which spans the waters of some 40 countries and territories throughout the Indo-West Pacific. The dugong is largely dependent on seagrass communities for subsistence and is thus restricted to the coastal habitats which support seagrass meadows, with the largest dugong concentrations typically occurring in wide, shallow, protected areas such as bays, mangrove channels, the waters of large inshore islands and inter-reefal waters. The northern waters of Australia between Shark Bay and Moreton Bay are believed to be the dugong's contemporary stronghold.

Like all modern sirenians, the dugong has a fusiform body with no dorsal fin or hind limbs. The forelimbs or flippers are paddle-like. The dugong is easily distinguished from the manatees by its fluked, dolphin-like tail, but also possesses a unique skull and teeth. Its snout is sharply downturned, an adaptation for feeding in benthic seagrass communities. The molar teeth are simple and peg-like, unlike the more elaborate molar dentition of manatees.

The dugong has been hunted for thousands of years for its meat and oil. Traditional hunting still has great cultural significance in several countries in its modern range, particularly northern Australia and the Pacific Islands. The dugong's current distribution is fragmented, and many populations are believed to be close to extinction. The IUCN lists the dugong as a species vulnerable to extinction, while the Convention on International Trade in Endangered Species limits or bans the trade of derived products. Despite being legally protected in many countries, the main causes of population decline remain anthropogenic and include fishing-related fatalities, habitat degradation and hunting. With its long lifespan of 70 years or more, and slow rate of reproduction, the dugong is especially vulnerable to extinction.

## Appearance

The dugong is an aquatic mammal with thick, tough, and smooth skin. The skin color of newborn dugongs is pale cream, darkening as they age, becoming deep slate gray on the sides and dorsum. The body of the dugong is sparsely covered with hair, and the muzzle exhibits bristles. The upper lip is cleft and muscular, hanging over the mouth, which is curved downwards. At first sight, dugongs look like whales, but they have evolved independently. They also develop tusks, which are visible in adult males. The dugong is also known as the 'sea cow' due to grazing on seagrass, although the closest relatives of this animal are not cows but elephants.

## Distribution

Dugongs are distributed across the Indo-Pacific region, where they live in highly endangered and nearly extinct populations. They are found from the east coast of Africa to Vanuatu and other islands of the western Pacific. The highest concentration of dugongs is off the coast of northern Australia, whereas the second largest population occurs in the Arabian Gulf. Feeding upon seagrass, dugong prefers living in shallow and protected coastal, tropical waters. They generally inhabit salty waters and can tolerate brackish waters but rarely occur in freshwater.

## Behavior

Dugongs are social animals but generally occur alone or in pairs of a mother and calf. However, they are known to form large groups of several hundred animals. As semi-nomadic animals, dugongs may either travel huge distances in search of specific seagrass or live in the same area throughout their lives. They usually have to travel when their main food, seagrass, is in scarcity. When suitable seagrass is depleted, they move on, looking for new areas of feeding. Due to living in turbid waters, these animals are extremely hard to come across unless they are disturbed. Dugongs are shy in their nature and when disturbed, they quickly flee. When they don't flee, they usually explore the vessel or diver from a distance without coming closer.

## Diet

Dugongs are herbivores (graminivores) and primarily feed upon seagrass. They will occasionally eat invertebrates such as jellyfish, sea squirts, and shellfish. Populations in Moreton Bay, Australia, feed on invertebrates such as polychaetes or marine algae.

## Reproduction

Dugongs are polyandrous, which means that one female has an exclusive relationship with two or more males. Dugongs may breed at any time of year. Males of this species are in constant search of receptive females. Reproduction usually depends on location, though they are known to have an extremely low birth rate, yielding a single young with intervals of 2.5-7 years. The gestation period is quite long, lasting for 13-14 months. Newborn dugongs are able to consume seagrass. However, it's maternal milk that helps them grow up at a fast rate. Young are nursed for more than 18 months, remaining close to their mother and typically riding on her back. Sexual maturity is reached within 6-12 years old in males and at 6 years old in females, although females of this species usually first give birth within 6-17 years old. Becoming mature, young dugongs rush to leave their mother, looking for mates.

## Population

### Population threats

One of the biggest threats to the population of this species is hunting for meat and oil. Dugongs are often incidentally caught in nets, targeting fish and sharks. This by-catch leads to high mortality because of insufficient oxygen supply. Ships, boats, and other vessels may strike these animals down throughout their range. Another notable threat is habitat disturbance in a form of water pollution, which leads to the destruction of seagrass beds that are the main food source for these animals. And finally, their population cannot increase due to the extremely low birth rate of this species. On the other hand, dugongs cannot be bred in captivity.

### Population number

According to the WWF (World Wildlife Fund), the overall dugong population is estimated to be about 85,000 animals, living in the waters of northern Australia, from Shark Bay (Western Australia) to Moreton Bay (Queensland). Currently, this species is classified as Vulnerable (VU) on the IUCN Red List and its numbers today are decreasing.

## Fun Facts for Kids

The dugong is the only sirenian in its range, which spans the waters of some 40 countries and territories throughout the Indo-West Pacific. These animals are called 'sirenians' since their mammary glands and nursing habits are similar to those of humans'. Hence, sailors often call dugongs mermaids or sirens.

The upper lips of these animals are very flexible, helping them snatch entire plants. After feeding, dugongs leave so-called 'feeding trails' - furrows, made on the seafloor.

Immediately after birth, female dugongs push their offspring to the surface to breathe.

In order to breathe, dugongs are known to stand on their tails, pointing their heads out of the water.

The dugong appeared about 50-60 million years ago, evolving from an elephant-like animal, entering the water.

Dugongs usually shake their head to clean seagrass from sand and only then swallow it.